Posts Tagged ‘Do-it-yourself project’
by Tom Gaylord, a.k.a. B.B. Pelletier
I’m still in Ft. Smith, Arkansas, as I write this, so please excuse the brevity of the report. A while ago, I wrote down this idea as a possible report topic. Those who haven’t yet come over to PCPs often wonder how reliable they are, and those who already have the guns sometimes encounter things that are common problems but new to them. Let’s talk about that today.
WARNING: The procedures I am about to describe are for those who know what they are doing. In every case, there are proper safety steps to be taken so accidents don’t happen. I cannot possibly describe all of those steps, so the following procedures are presented only for your education — not to train you as an airgunsmith. Safety with pressurized air and airguns should always be the No. 1 concern.
I can’t fill this airgun!
Boy, have I ever heard this one! It can come to you in a variety of ways, such as, “This airgun is broken — how do I return it?” I used to get at least one of those calls every month while I was the technical director at AirForce Airguns. The first few times I heard it, I was worried; but I got so used to hearing it that I would start telling them the cure before the problem had been fully stated.
The guy would tell me that he couldn’t fill his old-style Condor tank. I asked him how he was trying to fill it — from a scuba tank or with a hand pump — and a lot of times that made the guy mad. He wanted to know why that mattered because he should be able to fill the gun from a scuba tank or from a hand pump. Right? When this call came in, I knew he was filling with a hand pump, and I also knew he was trying to fill an empty tank.
The answer to “can it be done” is both yes and no. Yes, you can fill this kind of tank from a hand pump if there’s already some air inside it, and no, you can’t fill the tank if you start with it empty. That would really anger some people until I explained that the air inlet valve on an old-style Condor tank is also the exhaust valve. It’s a door that swings both ways. If there’s no air inside the tank, the valve will not recognize the small puff of air from a hand pump and will escape, again.
The valve will not close because it also uses internal air pressure to help it close tight. If you fill the tank from a scuba tank, the incoming air is under so much pressure that it will fill the tank quickly, and the internal air pressure will help close the valve when the filling stops.
A hand pump cannot fill some pneumatic airguns (not just Condors) unless they already have some air pressure inside to hold the inlet valve closed. We would ship tanks out with what we called a maintenance air charge in them — just enough pressure to hold the valve shut. But if the guy received the gun and then proceeded to shoot all that air out, as some of them did, they then had a gun that could only be filled from a scuba tank. It’s not funny when it happens to you.
This phenomenon is not just confined to AirForce guns, either. Almost all of the powerful Korean airguns work in a similar way. But the Korean guns can accept a charge by simply cocking the bolt — sometimes. In that case, taking the pressure of the bolt off the valve allows it to close and seal completely.
The newer style of Condor (as well as all other AirForce sporting PCP rifles) has a Spin-Loc tank with a separate inlet valve and firing valve. I’m not certain, but I believe this has solved the problem I just discussed. If I had a tank and pump here with me, I would check it right now. I’ll look into it when I get home.
Now you know two things about PCP “leaks” that are both very common problems and often misunderstood. First, they aren’t really leaks. They’re part of the gun’s design. Second, some guns must first be cocked to be filled.
Before you go all — “They shouldn’t design them that way!” on me, remember, the SR-71 Blackbird reconnaissance plane leaks fuel until it flies fast enough to heat and expand the airplane’s skin. Only then do all the leaks stop. Sometimes, a product can have a quirk that isn’t a flaw — it’s just the way it works. The Sheridan Supergrade rifle is one that cannot be pumped up unless the bolt is cocked first.
Use a hammer!
I probably shouldn’t tell you guys this next one; because when some of you get a hammer in your hands, every problem looks like a nail. But in the world of pneumatics, there are times when a big rubber mallet is exactly the right tool to use. When is that time? When a pneumatic that has been performing well all along suddenly develops a fast leak. It’s probably due to a piece of dirt that’s gotten onto a soft seal and is allowing air to pass through. To get it off the seal, it sometimes works to tap the end of the valve with a soft hammer. It opens the valve, and the blast of air will probably blow the dirt past the seal.
When I built valves at AirForce, I tested each by pressurizing them in a fixture and tapping the valve stem with a rubber hammer. I had racks of 100 valves at a time, and I went through and did this to each one in turn. That process seated the valve and created a small ring of contact between the synthetic valve and its seat. Sometimes, the valve needed to be hit several times to seat it properly, but it always worked. And it also worked if a valve had a small piece of dirt anywhere in the seals.
When customers would call with a gun that leaked and I determined the leak was a fast one that had popped up all of a sudden, I told them to try this procedure before sending the tank back for repairs. It fixed probably over 75 percent of all such leaks.
But this isn’t magic. If your gun has been a slow leaker the whole time you’ve owned it, this isn’t going to change a thing. It’s just for those all-of-a-sudden leaks that crop up sometimes. It will work for all guns, but most of them don’t allow direct access to the valve head like the AirForce tanks do. For those, you can do the next best thing — dry-fire the gun several times. That usually fixes the problem unless you’re timid about it. I sometimes had to get a timid owner to dry-fire his gun by telling him to fill it full and then dry-fire it 20 times in rapid succession. All that was doing is getting him to dry-fire the gun repeatedly without pausing to see if it was fixed yet. When there’s a piece of grit on a seal, it takes a lot of air flowing past to dislodge it, and a couple tries are often not enough. Twenty shots is probably overkill in all situations, but it saved me time from having to explain in detail just what the guy was doing — as I have now done for you!
You now know a genuine airgunsmith procedure! It isn’t as fascinating as it sounded, is it?
Okay, let’s go back to 1960, when cars had points and copper spark plug wires with (sometimes) poor insulation. Mechanics had a genuine stethoscope in their toolboxes. Or if they were shade-tree mechanics, like me, they had a 4-foot length of small rubber hose. We would put one end of the tube to our ear (the ear that worked best) and move the other end around the engine compartment while the motor was idling. You could quickly zero in on an arcing sparkplug wire or an exhaust manifold leak. It also works for precharged airguns!
You don’t need a hose because the barrel is the pipe that transmits the sound. Cock the gun but don’t load it. The sound you’re listening for is an air leak at the exhaust valve. But here’s an important safety tip — never put your ear directly over the muzzle and never do this if the gun is loaded! Listen from the side of the muzzle; so if the gun were to fire, the air would blast past your ear instead of into it! You can use a piece of paper to direct the sound, if needed. That keeps you safe and still lets you hear the smallest sounds.
I’ve found a number of valve leaks this way. This is just a diagnostic tool — it doesn’t do anything to fix the valve.
If your ears aren’t that good, or if you just don’t want to do it this way, you can also put a few drops of soapy water down the muzzle of a cocked gun. Bubble-blowing solution that you can buy at a dollar store works perfectly for this! If any air is escaping the valve, there will be bubbles at the muzzle. I always had a small bottle of bubble-blowing solution next to me when I worked on guns at AirForce. Of course, you have to clean the barrel and wipe it with an oily patch after doing this.
These little procedures have proven very valuable over the course of time. If the situation is right, they’ll fix the problem more often than not. While they seem simple to the point of being somewhat ridiculous, they do work.
by Tom Gaylord, a.k.a. B.B. Pelletier
Today’s report is a guest blog from reader Fred from the Democratik People’s Republik of New Jersey. It came from his ingenuity in dealing with a need that arose in the field. I’ve linked it to the recent .177 Marauder reports because it seems to fit.
If you’d like to write a guest post for this blog, please email us.
Over to you, Fred.
Fixing a Marauder magazine
by Fred DPRONJ
A number of factors led to this blog — the first being a scheduled benchrest .22 rifle competition my league was going to hold following our 25-yard bullseye competition. The second was, I believe, blog reader John. Or was it Mike? No matter. But whoever made the comment mentioned later in my report…thank you!
I had gone to the range several days ahead of the benchrest competition to sight in my .22 cal. Benjamin Marauder. For fun, I decided to take on the rimfire boys with my air rifle. It took roughly 6 pellets to get the scope sighted where I wanted. However, I could not see where pellet 7 landed. Two more shots and I was incredulous. The rifle had gone from hitting the 10 ring to missing the entire target paper and backer. At this point, I looked at the magazine and discovered it was not rotating to feed the next pellet. It was stuck after firing pellet 6. I assumed the internal spring had broken, so I packed up and went home discouraged. I didn’t have another .22-caliber Marauder magazine, so I might have to use my Ruger 10/22 for the competition.
However, I recalled John (?) mentioning in the blog comments that these magazines could come apart. At home, I carefully examined the magazine under magnifying glasses and saw that what I had believed to be a rivet in the center of the magazine was actually an Allen screw.
A 1.5mm Allen wrench fit; after initial resistance, the screw was removed.
The magazine is really an elegant engineering solution for the task of feeding pellets with a bolt action. It consists of 5 parts — an outer case, a coiled spring, the circular pellet holder, the clear plastic cover and the the screw that holds everything together. When I disassembled it, nothing appeared broken.
If you look very carefully at the coiled spring, you will note that the ends are different. While both ends are bent at 90 degrees, one is bent away from the coils while the other end is bent down to stick into a hole in the bottom of the magazine case.
One end of the spring is bent out at a 90-degree angle, while the other end (not visible here) is straight in line with the coils. This is the end that sticks into one of the holes in the bottom of the magazine case.
The end that you see in the above picture goes into one of three holes in the magazine case. Each hole gives a different amount of pre-load to the spring.
I decided to insert the spring into the hole nearest the bottom of the case, next to the cutout that slides over the breech when the magazine is installed. In the above photo, that hole appears at the 9 o’clock position, and you can see the cutout that goes around the breech very clearly.
Here’s the magazine spring. Now you can see both ends. The end on the left goes into one of those holes in the bottom of the magazine case, and the end that sticks out on the right fits into the slot on the underside of the pellet holder.
The straight end of the spring that sticks out, away from the spring coils, goes into the slot in the underside of the pellet holder. It’s just a matter of approximating position of the holder’s slot to the spring and moving it back and forth until the spring end clicks in. You easily feel when it pops into the slot.
The pellet holder has a circular groove in it, and the brass pin of the cover moves in it. The groove is almost a complete circle, but the part that isn’t grooved allows the cover to rotate the pellet holder against the coiled spring when the magazine is loaded.
The magazine case with the spring and the pellet holder in place. Notice the circular groove in the pellet holder, next to the numbers. This is where the brass pin of the cover fits, allowing the pellet holder to move as the pellets are pushed out of the magazine by the bolt.
With the pellet holder in position, I pressed it down and slid the clear plastic cover over it and then aligned the cover with the magazine case and inserted the Allen screw. [B.B.'s note: The brass pin in the bottom of the clear plastic cover has to be inside the circular groove of the pellet holder, and the pellet holder stop (the portion of the pellet holder that protrudes) must be to the right of the shelf inside the magazine's outer case.]
I slide the clear plastic cover over the pellet wheel to keep it in constant contact with the coil spring so the end of the spring would not come out from the notch on the underside of the pellet holder.
The secret of my feeding problem was now revealed. The screw that holds the cover should be tightened only enough to remove any excess slop between the clear plastic cover and the magazine case. Too much tightening and the cover binds the pellet holder, preventing it from turning. The screw has an interference fit so it won’t back out when you rotate the clear plastic cover to load. Lifting and rotating the cover 90 degrees and releasing, the cover now snapped back with authority — indicating the assembly screw was tight enough and the magazine spring was doing its job. I was now set for my benchrest competition.
If this procedure seems confusing, believe me — it clears up when you have the 5 parts of the magazine in your hand. I have given you all of the references you will need to assemble your own magazines, should you attempt this yourself.
[B.B.'s note: I disassembled and assembled my Marauder magazine several times following these instructions. They do work.]
by Tom Gaylord, a.k.a. B.B. Pelletier
Today, blog reader Vince continues the saga of converting a steel spring rifle to use a gas spring. We last read about this project in Part 2 of I’ve got gas, where he showed us the pitfalls of making such a conversion to a Gamo breakbarrel. Let’s see how he does the second time around with a Crosman rifle.
If you’d like to write a guest post for this blog, please email us.
Back when I tried reworking the Crosman gas spring retainer, I discovered that drilling a straight and properly located hole on a round surface is a bit, well… tedious. And hard to do, at least without the proper drilling jig.
Of course, it would be very expedient to use the spring tube itself as a jig. After all, it’s perfect — as long as I can keep from damaging it, that is — because all the holes are obviously already in the right places. Put the retainer in place, pop in the pin and go at it through the existing bolt hole.
Two minor problems became apparent. First, the hole is too large to properly guide a 1/4-inch bit. Second, the edges of the bit might damage the existing hole in the spring tube. But both problems have an obvious, simple and cheap solution: a bushing.
Bushing for under $1.00 from McMaster-Carr.
I got mine from McMaster-Carr (part #2868T44) for less than 70 cents. If you’re feeling rich, you can probably get an equivalent at Home Depot for about $3.00. The important thing is that it has a 1/4-inch inside diameter, a 5/16-inch outside diameter, and that it be made from brass, bronze or steel. Plastic probably isn’t a good idea.
The process is simple — and THIS time I’m doing it on a Crosman rifle instead of a Gamo. No particular reason, I just wanted to show that it works on the Crosman platform as well. Specifically, this is a Crosman Sierra Pro, but mechanically it’s the same as the other Quest variants.
It looks like a Gamo, talks like a Gamo…
I ran into a bit of a problem sliding out the piston — it seems that the scope stop screw that I identified in this picture was binding the piston. Backing it out one turn solves the problem. As expected, the threaded hole in the Crosman gas spring retainer doesn’t align with the one in the spring tube — just like the Gamo.
The Nitro-Piston gas spring retainer…
…and why it doesn’t work.
So, what we’re gonna do is turn it 90 degrees and drill a hole on the other side.
This is where we have to drill.
See that little ledge sticking into the hole? I’m going to grind it out of the way:
Ground a flat spot, just in case.
In retrospect, though, this step may have been unnecessary.
Setting up the jig is about as straightforward as it gets. After installing the gas spring retainer and securing it with the retaining pin, I place the bushing in the hole in the spring tube and start drilling. The steel is pretty soft, so it’s not that difficult.
The bushing sits in the hole and is the jig for drilling. Simple!
But I only drill about half way and for a very good reason. If I keep going like this, I’ll hit something I don’t want to hit. Not a water or gas main, but that retaining pin is very definitely in the path of that drill bit. The solution is to slide the pin almost all the way out (but still engaging the retainer on one side); so when the bit breaks through, the pin won’t be damaged. Drilling the rest of the way thus proves uneventful.
Don’t want to drill through that pin.
Next comes the tapping — M8x1.25 inches, which is very close to 5/16-inch NC. If you don’t have a metric tap, get one. Do NOT try to make the SAE size work. You’ll regret it if you do! But my old and worn tap steadfastly refuses to start because it wants something a tiny bit bigger than 1/4 inch, so I have to bore out the hole to 17/64 inches. That makes all the difference, and a few minutes later I have a properly tapped hole.
Just a smidgen bigger…
…before I can tap the hole.
A quick test-fit shows that everything goes together just as it should.
As for the rest of the work, it’s a simple matter of cleaning everything out, lubrication and assembly. If you recall, the gas spring got scratched up from rubbing on the piston in my Gamo 220, so I colored those scratches with a Sharpie. That way, if I wind up with more rubbing in the same place, it’ll be readily apparent.
After a good cleaning, everything goes back together just as I described for the Gamo. But don’t forget that little disc that goes into the retainer.
I suspect this may be important.
One thing I sort of glossed over last time is how to get that pin installed. Since the gas spring has all of about 1/8 inch of preload, the pin can be started using a screwdriver to pry the retainer into place.
Prying the retainer to start the pin.
That’s good for getting the pin started. But you won’t be able to get it the rest of the way through because that spring is still pushing the retainer rearward, and the itty-bit of slop in the whole thing means that the holes won’t quite line up on the other side of the tube.
The solution is easy enough. Once it’s started, tap the pin in until it gets to that point. Then, lay the action on its side with the protruding pin downward, and push down on the spring tube while tapping the retainer with a hammer or mallet. The impact of the hammer will make the retainer jump forward just enough to momentarily line up the holes and allow the pin to start coming through. Three or four taps ought to be enough.
Tapping the retainer allows the pin to slide home.
The only minor difference between this Crosman gun and the Gamo is the endcap, which on the Crosman slides inside the tube. It’s a little different from the one that comes installed on the springer:
The gas spring endcap is on the left, the original on the right.
The gas spring version just slides into the rear after it’s all together, and we’re done!
Don’t forget to tighten the scope stop screw.
The action reinstalls in the stock with no mismatched screw holes.
Shooting it demonstrates the same sort of changes in behavior as with the Gamo I converted, only more so — and less so — all at the same time. For one thing, it runs a little hotter than it did in the Gamo. With the same RWS Basic pellets, it did the following:
That’s an average of just about 1000 f.p.s., or 15.5 foot-pounds of energy. This represents an improvement of just about 100 f.p.s. over the original Crosman powerplant.
Firing behavior and feel, however, wasn’t as vastly different as it was in the Gamo. The Crosman “sproings” a fair bit less than its Spanish forebearer (the rear guide tends to be a tighter fit); and with a tarred spring, the smoothness of the firing cycle is pretty close to that of the gas spring.
After I returned the Crosman to its original configuration, I was able to examine the gas spring for any damage. Oddly enough, there was some scratching again but nowhere near as bad as the last time and only on the front 1 inch of the cylinder. So, it’s not related to the centering of the gas spring at all. I suspect the end of the cocking link may have been rubbing it.
I remember a while ago a reader asked about the specs of the gas spring, in particular its pressure. I decided to measure that using my high-precision bathroom scale (!) and a Chinese hydraulic press. This was a quick and dirty way to get a ballpark figure. The pressure was almost constant as it was compressed but not quite. It did creep up just a bit, starting at about 130 lbs. and ending in the vicinity of 150. Overall length of the spring is 10.25 inches with a cylinder diameter of 0.715 inches.
And that pretty much wraps up my gas attack. Exactly where does that leave us?
Well, we’ve shown that the gas spring conversion is certainly doable. It’s not as straightforward as I would have liked — buy a few parts and stick ‘em in — but it’s not beyond the realm of the average handyman. The gas spring itself pretty much lives up to its reputation… smoother, somewhat harder to cock for a somewhat elevated power level. The big mechanical advantages — no coils to break, no degradation from being cocked for long periods of time — are already well-known. The main subjective advantage, the smoothness of the firing cycle, all depends on how bad was it to start with. In a 10-year-old Gamo, the improvement is likely to be rather spectacular (especially in an untuned gun), but if the rifle is already a smooth shooter, less is going to be gained. I guess it just comes down to personal preference — whether it’s worth $50 and a couple hours of your time is up to you.
by Tom Gaylord, a.k.a. B.B. Pelletier
Today, we’ll finish the conversion of a Gamo 220 from steel spring to gas spring, and blog reader Vince gives us a report on the outcome.
If you’d like to write a guest post for this blog, please email us.
Take it away, Vince!
When we last saw the Gamo 220, I’d disassembled the powerplant and compared the old parts to the parts I ordered from Crosman. Today, I’ll install those new parts and test the gun for you.
The gun is laying on the bench, ready for assembly. The new piston slides in, followed by the gas spring. Be careful when sliding the piston seal past the end of the cocking slot and tuck the soft seal material away from the sharp edges of the cocking slot so the seal isn’t damaged. A flat-bladed screwdriver works well for this.
The new piston that works with the gas spring is slid into the spring tube. Notice that I’ve lubricated both ends of the new piston with moly grease.
The new gas spring (Nitro Piston) slides in after the piston. The small end of the spring fits into the socket inside the new piston I mentioned in Part 1. No lubrication is required.
The trigger and cocking link go back in (reverse order of removal), and the plain plate gets dropped into the rear spring retainer.
I’m dropping the plain plate into the rear spring retainer.
Now, I’m starting to sweat a bit. You see, I KNOW that the gas spring has a TON of pressure on it even when fully extended (very much unlike a coil spring) — so, how on earth am I gonna compress it enough to reassemble the gun? Oh, well, I’ll cross that bridge when I come to it –which is, well, right about now. After I install the rear retainer, I notice something.
There’s almost no preload on the gas spring
Almost no preload at all! THAT’S right. Because the gas spring is ALWAYS at or near full pressure, there’s plenty of preload pressure as soon as the piston comes off its stop, so very little preload travel is required.
What is preload?
When a conventional coiled steel mainspring is installed in a spring gun, it’s usually longer than the space into which it must fit. It is, therefore, necessary to compress the spring by some amount to get it to fit inside the spring tube. This compression causes the spring to be under pressure even when at rest — this is called preload. If you’ve ever seen a long, empty flatbed trailer on the interstate that looked bowed up in the center because there’s no weight on it, you’ve seen what no preload looks like. It takes several tons of weight just to get that trailer flat again — and much more to make it bow the other way.
Airgun tuners can add spacers that preload the mainspring even more when it’s resting, which causes it to develop greater power when compressed because it’s closer to its maximum potential that exists at the point when all the coils are touching. But gas springs don’t work that way. They’re under full compression (internal gas pressure) when they’re at rest. All cocking the gun does is move the internal piston against the already-compressed gas that’s ready to blast it back when the sear releases it. There’s a very small amount of additional compression of the gas, but it isn’t what makes the gas spring work as well as it does. The gas spring unit is always at full potential — even at rest.
So, this gas spring unit has very little farther to go at this point…under a quarter-inch, in fact. THIS sure makes things easy for me. Pry the retainer forward on one side while starting the pin through the other. [Note: If I used a mainspring compressor, I wouldn't need to pry anything. I would just tighten the compressor until the assembly pin holes lined up, then insert the large crosspin.]
The crosspin will go in, but the hole for the rear spring retainer bolt (that large-headed bolt I removed when I disassembled the powerplant in Part 1) doesn’t line up with the hole in the spring tube. This is a problem.
Immediately, a problem becomes apparent. Look at the hole where the rear spring retainer bolt goes. It’s not lined up with the hole in the tube. There’s approximately a .080″ misalignment here. This ain’t gonna work. My first inclination is to simply elongate the hole. But when I reinstall it, there’s another problem.
There’s a gap between the plate on the spring retaining bolt and the trigger assembly. It won’t support the trigger this way!
The trigger isn’t properly supported by the plate that’s attached to the bolt. Worse, this changes the spacing between the front and rear stock screws and doesn’t allow the action to be reinstalled.
Hmmm. I’m wondering if this is exactly what Crosman (or BAM) had in mind — preclude an easy conversion with existing parts (since the same problem would exist on a normal Quest). That leaves me thinking: Can I just butt the gas spring against the original Gamo spring retainer?
If you look at the picture of the new rear spring retainer above, you’ll see that there’s a small plate that drops into the cup that retains the gas spring cylinder. The cylinder wants to butt up against a flat surface, and the Gamo retainer has a large (approx. 1/2″) hole in it. I need a metal plate to go over it. Wait a minute! I’ve got one right here in my pocket!
A perfect spacer for the new gas spring and it costs — well, about a quarter!
And, so, it gets reassembled. Believe it or not, the whole thing works.
Time to test!
I’ll run through this pretty quickly — the velocity is now up to about 964 f.p.s., which represents a muzzle energy of about 14.5 ft-lbs. Not killer, but obviously a lot better than the detuned gun. Accuracy shouldn’t be changed — or should it? Oftentimes, guys will detune their guns to make them more accurate — or to simply make them easier to shoot. That might have some merit, as I now couldn’t break 0.37 inches at the same range. Not a big difference, and I’m certainly not gonna suggest that the gas spring decreased accuracy. But I don’t think it helped.
So what’s it like to shoot?
First of all, everything anyone ever said about “thunk” vs. “sproing” is absolutely correct. The gun “wumps” with a gas spring, and you can actually feel a kick back into your shoulder. Nothing like a typical centerfire gun, although maybe something like an 1894 shooting low-velocity .38 specials might be comparable. But that’s just a guess.
Cocking the gun is another matter. Effort peaks at about 33 lbs., which isn’t all that high — except for the fact the effort before that peak is certainly a lot higher than with a normal coil spring. This is what we’d expect, of course, with the relatively constant pressure of the gas spring. It isn’t unbearable, but it does take some getting used to.
Back to a coiled steel mainspring
After about 40-50 rounds, I decided it’s time to restore the gun back to original spec. I rummage around my spring box and find a REAL low-mileage Gamo spring, and put it all back together the way God intended it. NOW, I can really get a back-to-back series of impressions.
First, the velocity did drop a smidgen. It’s now down to an average of about 943 f.p.s., or a little under 14 ft-lbs. Second, and despite the tar on the spring and rear guide, we DEFINITELY are sproinging ourselves rather energetically. Lastly, the cocking effort is predictably much milder. Peak effort is down by 5 lbs., and the effort before that peak is even easier. Accuracy is unchanged from the gas spring.
How did my quarter, er, my impromptu gas spring backing plate pan out? Not too well.
The pressure of the gas spring punched a deep divot into the quarter.
The flip side doesn’t look any better.
I flattened it back out with a hammer, and I’m really hoping it’s still legal tender. Anyway, as I sort of expected, the relatively soft quarter didn’t do well. The backing plate really ought to be steel, 0.060 inches (1.5mm or 1/16″), just like the original.
But the bigger problem wasn’t the quarter.
There’s a serious indication of metal-to-metal galling.
There was some serious metal-to-metal contact going on here between the cylinder of the gas spring and the inside of the piston. If you look at the above pictures of the quarter, you’ll see that the indent isn’t centered. The pocket in the original rear spring retainer keeps the spring cylinder right in the middle, and apparently that’s real important because it won’t center itself.
And that’s about it for now. If this is going to work, we need a simple and cost-effective way of keeping the gas spring centered properly without permanently altering the original parts…and do it in a way that the average tinkerer can accomplish on his own. The first thing that comes to mind is to drill and tap a new hole in the new rear spring retainer, opposite of and slightly forward of the existing hole. I tried that, and found (predictably) that getting the hole in just the right spot is a bit difficult without a custom drilling jig.
For now, I’m just going to give it some thought.
WAIT! I JUST GOT AN IDEA….
by Tom Gaylord, a.k.a. B.B. Pelletier
Today, we’ll have the first part of a guest blog from reader Vince. For those who don’t know him yet, Vince is our “go-to” guy for fixing all sorts of strange vintage airguns. In this post, he tells us the tale of a wild idea he just had to try.
If you’d like to write a guest post for this blog, please email us.
Over to you, Vince!
“Nitro” is da bomb, right? I mean, in current usage, “Nitro” anything means hot, fast, powerful and overall bad. This normally benign element sure shows its alter-ego when combined in properly mischievous proportions with oxygen to form nitrous oxide. More fun can be had by mingling it with oxygen, carbon, and hydrogen in various arrangements to come up with nitromethane, nitroglycerin, nitrocellulose or TNT (trinitrotoluene). So, yeah, “Nitro” IS da bomb — in every sense of the word.
Now, when Crosman started producing the Nitro Piston series of air rifles — well, it sends the imagination reeling, doesn’t it? That is, at least, until we come back to reality and realize all they’re doing is using something called a gas spring, which uses pressurized nitrogen to exert pressure on a piston-rod and cylinder assembly. Push the rod in, and it pops right out again, with different degrees of enthusiasm, per the individual design of the particular gas spring.
The advantages of the gas spring in an airgun application are numerous. Because there’s no metal coil spring inside, the gun doesn’t FEEL like there’s a metal coil spring inside. No twang, sproing, buzz or anything else of that nature — and no twisting or torquing reaction as the spring extends and slightly unwinds. Because gas doesn’t fatigue, a properly functioning gas spring will never take a set or get weaker with time. This also means you can leave it cocked for as long as you want with absolutely NO effect on spring life.
What’s not to love?
Well, specifically, those two little words…”properly functioning.” Yes, the gas will never fatigue, but sometimes it leaves home and never comes back. And if the gas spring DOES leak, there’s nothing left to do except go get another one. And almost certainly, it means going back to the manufacturer — and praying that they still have them available.
You see, gas springs are something of a specialty item. They kinda have to be designed around a specific application. There are universal gas springs out there, but the chances of finding one with parameters comparable to your airgun is gonna be difficult. Unlike a coil spring you can’t just get a longer one and cut it to length. You can’t tell what sort of rate a gas spring has (or had) just by measuring things, like you can with a coil spring. I believe you can still get custom coil springs made on a case-by-case basis, but making a gas spring is a bit more involved. Heck, you can make a crude coil spring yourself using a paper clip and a pencil. Sure, it won’t be good for much — but it shows that the basic process for making one is, well, pretty basic.
That’s why I’m not terribly tempted by all these Nitro Piston (of any sort) air rifles that are out there. Will you be able to get it working 50 or 75 years from now? I certainly won’t, cause I’ll probably be gone by then. But that’s beside the point. I’ve got future generations in mind here! I don’t want little Billie- or Betsy-Bob cussin’ out their great granddaddy simply because he bought a gas spring rifle they can’t fix. Heaven knows they’ll probably have enough reason to do that anyway. Why add fuel to the fire?
That’s when I got to thinking. How about gas-springing a spring gun? When the gas stuff craps out, I (or whoever) will easily be able to cram in all the old conventional spring stuff and the gun will be back in business. After examining the Crosman gas guns (for some reason this makes me think of the “fart gun” from Despicable Me), it seemed obvious that they’re based on the ubiquitous Quest platform. That rifle, as we all know (except for those of us who don’t) goes back to the old BAM B18/B19 air rifle. Which, in turn, was a near-clone of the old steel-barreled Gamo series of the time (Shadow, 220, 440, 890, etc.).
Seems to me that a proper pickin’ of replacement parts ought to let ANYONE with a Quest variant (which are as numerous as the stars in the sky) or a Gamo 220 variant to gas ‘em up without giving up long-term serviceability. The best part is that Crosman is generally the most tinkerer-friendly airgun company out there. Not only do they sell parts — ALL parts — for many of their springers, but they’ll sell them to anyone. And they’ll let you keep your first-born, your arms and your legs, and your very soul because their prices are so reasonable.
So it is that I started combing through the parts list for the Storm and the Titan GP air rifles. My suspicion of the close relations was confirmed by Crosman’s designations for these guns — both start with C1K77. I believe C designates the gun family, the 1K means 1000fps, and the 77 points to .177 cal. In any event, the commonality of parts (especially the cocking link, trigger assembly and piston seal) tells me I’m on the right track. Things can get a little tricky, as some parts that are virtually identical might have different part numbers depending on cosmetic details (like lettering). Trusting my own judgment, I came up with a list of 5 parts that I THINK will fill the bill:
Back spring guide…..BT9M22-00-2
I ordered the parts and waited. As a side note, I told the customer service rep at Crosman what I was trying to do, and he seemed rather interested in my results. I think I’m gonna just send him a link to this blog. As another side note, there’s some commonality between Crosman’s part numbers (which were revamped a couple of years ago) and Stoeger’s. Of course, both guns are made by BAM in China.
A week or so later, the package arrived!
The parts received from Crosman. The camera perspective distorts the gas spring at the hottom. It’s really straight.
Picking a guinea pig is easy. I immediately turn to a tried-and-true, long-time member of my collection: a Gamo 220.
My Gamo 220 was the guinea pig.
The Gamo 220 is a bit of a mule, frankly. All the 1000 fps Gamos of that period used essentially the same powerplant with a 25mm bore, a 100mm stroke, and the same 29 lbs./in. spring. The Shadow, which was the first decent airgun I ever bought, had a nice-to-hold, if utilitarian, synthetic stock and the low-grade rear sight. The significantly more expensive 440 had a nice-looking wood stock with Gamo’s “better” micro-metric rear sight (which, incidentally, is actually inferior to the lower grade one). The upscale 890 was a sightless 440 that came with a scope.
The 220, price-wise, sat in the middle — with a completely unadorned, mud-brown and slippery wood stock with about as much aesthetic appeal as an old shoe. It lacks the utilitarian friendliness of the Shadow and the visual appeal of the 440/890. It really was the least-appealing of the Gamo magnum breakbarrel lineup. Why do I have one?
As a result, it periodically becomes a test-bed for projects when I don’t want to mar up a NICE gun. Projects like this one.
The first thing I do is baseline the rifle for accuracy and power. In the accuracy department, it didn’t disappoint — a 0.30-inch 5-shot group at 36 feet. That’s about what I remember for the gun. Power-wise, however, was a different kettle of fish. I used RWS Basic pellets for velocity and averaged only 814 fps with a spread of 22 fps. The spread isn’t too bad, but the velocity stinks and represents a measly 10 ft-lbs of power. Oh, well. Frankly, I don’t even remember what guts are in this thing.
The gun comes apart in pretty much standard Gamo/Quest fashion, starting with the three stock-to-action screws. Once the action is out of the stock, you go to the rear of the spring tube, where the big bolt comes out first.
The big bolt comes out first. Then, the pin is drifted out, but only after the end cap is restrained.
The pin is next, but the rear retainer has to be suitably restrained in order to contain the approximately 2 inches and 60 lbs. of mainspring preload typical for these Gamo’s. Or not, as the preload in this gun turned out to be less than an inch. What happened? We’ll find out soon enough.
Next step is removing the trigger, which means the barrel has to be broken open so the trigger can slide backwards a bit.
Break the barrel to put slack in the cocking linkage. The slotted bar that runs back to the trigger is the link for the anti-beartrap device.
Then, the cocking link gets pulled down, freeing it from the piston and allowing you to disengage the anti-beartrap link.
The cocking link can be disengaged from the piston, then the anti-beartrap link disconnects from the cocking linkage.
At this point, the piston just slides out. So — what’s up with that low power and lack of preload?
Wow! That mainspring sure is short. And that rear guide AIN’T Gamo.
Oh, yeah — that’s right. I detuned this thing with a Crosman 500X spring. Incidentally, that spring is part #B12-1-00-4A, for anyone who wants a real pleasant detune on a similar Gamo or a Quest variant. That’s why velocity was so low and why I could cock it with my pinkie! That also explains the lack of preload.
But the guide? Near as I can tell, it was a custom guide I picked up somewhere. It’s dimensionally close enough to the normal Gamo parts that I can be sure it isn’t affecting power.
The spring guide in my 220 (top) and a regular Gamo spring guide.
As a matter of curiosity, I looked at the two pistons side-by-side.
The new piston that goes with the gas spring (bottom) has a slightly shorter stroke than the old piston.
The upper one is the original — and it’s a little shorter, but it appears that, for whatever reason, the gas spring wants a slightly shorter stroke than the coil spring. Also — although it’s hard to tell from the pictures — the inside of the old piston has a flat surface for the top hat, while the newer one has a shallow hole meant to locate the rod end of the gas spring. You will see why this is needed in the next installment.
That’s where we are going to leave this story for now. Vince has the old parts out, and the new parts ready to install. We’ll see what happened in the next installment.
by B.B. Pelletier
BSOTW winner Stephen Carolyn Donahue says this about his winning picture: “Most of our children, posing with air rifles purchased from Pyramyd Air, three years ago. Please note that none of these weapons were loaded in this picture.”
I am attending the NRA Annual Meetings in St. Louis today, so I’m asking the veteran readers to watch out for new readers who need their questions answered before I can get to it. I’ll be back in the office on Tuesday.
Today, I want to talk about mixing airgun features that don’t go well together. I see this in two main ways. One is a thread on a forum in which someone touts a certain feature, such as a 24-inch barrel on a CO2 rifle. The thread that follows looks like a line of lemmings stepping off the same cliff as the originator of the thread. What if 24-inch barrels don’t do well on CO2 guns? No matter! Off they go in a race to change over all their CO2 rifles to 24-inch barrels, and someone wonders aloud where he can get a 30-inch barrel.
The other way I see this is in questions. They never come out and say what’s really on their mind, but a careful reader can usually see it just below the surface. “Where can I get a 6,000 psi nitrogen tank?” [...so I can fill my PCP rifle to 6,000 psi so it will shoot faster, flatter and straighter -- won't it?] Or they ask where they can get something “repaired.” I have a Sheridan Blue Streak that needs the barrel attached.” [...because when I mounted a 24x scope on the gun it cracked the solder joint and the barrel fell off.]
I gave you all a good look at what happens when someone acts on an idea they have without thinking it through. Remember Steel Dreams? That was an oversized Beeman R1 through which the builder planned to shoot .22 pellets as fast as a .177 R1. In other words — break the sound barrier. If you recall, the rifle weighed over 11 lbs., cocked with 75 lbs. of effort, had an Anschütz match barrel and was no more powerful than a normal R1.
And so it goes
But these stories don’t dampen the passions of the armchair tinkerer, because in his world all it takes to invent something is to imagine it. No metal is required, no machine time, no need to test whether that longer spring will even fit into that “underpowered” spring gun. Just the knowledge that he is right sends him off to the races.
Writer Ladd Fanta once wrote of a reader of his who “invented” the perfect airgun. It had to be fully automatic, have a plastic body so all the parts could be seen and cost less than a hundred dollars. He wasn’t talking about an airsoft gun, either. No, sir! he wanted a full-blown accurate and powerful pellet rifle with all those features.
Comedian Tim Allen got it right when he recognized the male need for more power in everything. What he missed entirely was the male resistance to doing work to get it! I can’t begin to count the number of times I’ve heard something like the following. I bought the new Dragon Spittle Extreeeeme because I thought it was the most powerful air rifle made. But I can’t cock it! I am a healthy 15 year-old and large for my age, but my father can’t even cock this rifle more than once. Why do you sell such a powerful rifle that is impossible to cock? He might as well have asked why sports car seats are so small or why 180-lb. beer kegs weigh so much!
You meet this same guy on a double diamond ski slope with his face planted firmly in the snow.
I want the most accurate, most powerful pellet rifle made, and I don’t want anything made in China or Turkey. And it has to cost $125 or less. Well, start working, Bunky, because you will be the first to build one, if you can!
Why don’t they…
… make barrels longer? Because everybody knows that longer barrels are more accurate. Oh, really? Then why, pray tell, are Olympic target rifle barrels 16 inches long, when the barrel shrouds that house them are 25 inches long?
… make better hunting air pistols? Could it be because it takes a long barrel to produce the power needed for a hunting airgun? And what’s wrong with the TalonP?
… make PCPs that sell for under $100? I’m actually working on that one.
… turn 10-meter target rifles into more powerful rifles for field target? Everyone knows 10-meter rifles are the most accurate in the world. Actually, Walther did just that about a decade ago. I worked on it through Smith & Wesson. They called it the Dominator, and it was supposed to sweep the field of all the prizes. The other competitors didn’t get the memo in time, I guess.
… make a BB gun that’s accurate? They did and they still do. The Diana model 30 was such a gun and is still sold in Europe, but the thousand-dollar price scared away American buyers. The Daisy Avanti Champion 499 is still a very accurate gun, though it competes at just five meters.
I’m as guilty as anyone
Many years ago, I had an “idea” that it would be nice to own a reloadable .22 cartridge that performed like the long rifle, but one for which I could cast bullets. So, I set out to build it. First, I ordered an E.R. Shaw .22 barrel with a 1:10 inch twist and forced them to chamber it in .22 Hornet. They balked because the Hornet twist is supposed to be 1:14 inch, but I knew better. They did what I asked and afterward they announced they would lo longer make .22 Hornet barrels!
I envisioned driving a 50-grain lead bullet at 1,200 f.p.s. and having the equivalent of the .22 WRF (or better still, the much older 22/45/10 single-shot from which the .22 Hornet was derived). Twenty-two ammo was up to $20 a brick and this was a chance to stick it to The Man. I never checked the availability of .22-caliber bullet molds (there aren’t many) or of custom mold makers who make .22 molds (there are next to none who do). I just assumed all the molds I needed would be there when the time came.
What I ended up with was an inaccurate .22 Hornet that didn’t like cast bullets or jacketed bullets, either. I had the barrel rechambered for .219 Donaldson Wasp — another cartridge that is supposed to have a 1:14 inch twist. I’m still playing with that one — trying to get it to work, because underneath everything there is a fine custom E.R. Shaw .22 barrel.
So, what gives?
Why do people want things that are impossible? I think I know. I think they read a few “facts” and become fixated on them to the exclusion of everything else. You can’t tell them anything because it’s way too loud inside their heads. They “know” they’re right and that others have simply missed the wonderful thing of which they’ve dreamed. Until they attempt to do something about it, they will never know the truth. They sit back and view the airgun world as one large buffet, putting things from every dish on their imaginary plate. From this, we get requests for pocket-sized air pistols with 50 foot-pound power and minute-of-angle accuracy. Or 30 foot-pound spring rifles that cock with 20 pounds effort and cost less than $150.
I’m just ranting now; I don’t expect an answer or think this will ever change. It must be part of human nature.
by B.B. Pelletier
This is going to get a little confusing, because I’m changing things in midstream. Part 1 of this report was titled Testing the Slavia 631 with non-lead pellets, because that was what I thought I was going to do. Instead, though, my Slavia 631 needed attention, and, while trying to fix it, I broke it. I tested the non-lead pellets with my FWB 150 and found them to be so accurate that a whole other test was born. I haven’t done that test yet, but today I’m getting back to the Slavia, which has recently been repaired and returned to service. There’s enough of a story in just fixing the gun, that I thought I would make a report out of it, plus I want to use the Slavia as a testbed for other things in the future and I needed to establish it as a working airgun again.
Confused? I know I am.
When I used the 631 to test the velocities of the various pellets that would be used in the test, I noticed the rifle was very hard to cock. I believe it took 35 lbs. to cock the gun, which is way out of profile for that rifle. I thought I’d do a quick lube job and see if things would return to normal. Well, they did, but not entirely.
After lubrication, the cocking effort dropped to 21 lbs., which is about where I expected it to be; but while assembling the gun, I had difficulty getting the trigger to work right. Then, during the final disassembly, I lost the small coiled spring that fits between the trigger blade and the sear. The sear is held on a pin inside the end cap, and this spring that fits into a hole in the end of the part helps hold it in place for the trigger to act on it at the right time.
The spring I lost is about half the diameter of a ballpoint pen spring, so it’s really tiny. Nothing in my small collection of spare parts was close. I inquired of several places, but nobody had a replacement. Then, while reading a blog about the disassembly of the 631 on Another Airgun Blog, I discovered there is a second spring that acts as the trigger return spring that I had never even seen. So I thought I had lost that one as well. I didn’t, but the way the blog was written, there was no clue as to where this spring fit or where I should look for it.
So, I switched test guns over to the FWB 150, which proved very serendipitous, because I discovered that non-lead pellets can indeed be accurate under just the right circumstances. But that left me with this broken classic 631 on my hands.
I remembered that I’d purchased the rifle from Compasseco, so I contacted Eric Munson, the son of the former owner, to see if he still had any Slavia parts. He didn’t, because Compasseco had gotten rid of them years ago when they stopped carrying the Slavia line. Then, I asked the right question. Did he have any old broken 630 or 631 rifles laying around? He did, because airgun dealers frequently have piles of guns they never fixed for one reason or another.
To cut to the chase, Eric sent me an old broken 631 that had been cocked for many years, and I was glad to get it. It had the tiny spring I needed, but it had something even more important. In that rifle, I spotted the trigger return spring that was not completely described in the blog I’d read. It’s a permanent part of the plastic triggerguard and stays inside the stock when the action is removed. Sure enough, when I looked inside my good rifle’s stock, there was the spring I thought I’d lost.
Trigger adjustment screw (second from left) is key to the assembly of the rifle.
Looking down through the trigger slot in the stock, you can see the trigger return spring that’s captive in the triggerguard. What appears as a square hole in this photo is actually a slot the trigger blade must fit through. There are two flat steel parts that together look like one in this view.
This view shows the trigger return spring better, and you can see how the trigger blade passes through the slot in the spring. Note the screw threads on the left that are part of the trigger-pull adjustment system. These are the key parts that must be assembled correctly or the rifle will not function.
Now, I’ll describe how a Slavia 630/631 is disassembled so the owners who have never done it will be able to follow my description and not make the same mistakes I did. This will not be a astep-by-step set of instructions because, in my opinion, the Slavia 630/631 is not a rifle for the beginner to work on. If you can understand what I’m showing you and telling you, you’ll be able to work on this rifle. If not, please don’t try to take it apart!
The action comes out of the stock by removing three long bolts — two in the underside of the forearm and the rear triggerguard screw. After the action is out of the stock, look down in the stock at the underside of the triggerguard to see the trigger return spring that Slavia also uses as a trigger adjustment. This is the spring that foiled me, and it will foil many of you unless you know where it is. The two photos I’ve already shown will reveal how these parts fit together.
You don’t have to do anything with this spring except to know that it’s there and how it functions. When the gun goes back together, the placement of this spring will determine whether your trigger works or not, and it’s very easy to get it in the wrong place.
The rest of the disassembly couldn’t be much easier. The first step is to drive out the one and only pin that holds the trigger blade. Once that’s done, the trigger blade can be pushed forward and up and will clear the sear, making it possible to remove the trigger blade and coiled spring from the action. There’s no easy way to explain this, but a few careful moments of fiddling with the trigger blade will do it. Be careful not to lose the tiny coiled spring that’s in the front of the trigger blade at the top and in the end of the sear.
The trigger pin is out. The tiny coiled spring that fits between the trigger blade and sear is not shown. The sear is still inside the end cap, held by a similar pin on the left side of the end cap. The long slot in the top of the trigger blade is for the automatic safety button. The piston pushes the trigger out of the way when it comes back during cocking. It pushes the automatic safety button back until a ridge on it cannot allow the trigger to move. The knurled knob at the right of the end cap is the automatic safety.
Once the trigger blade and sear spring are out of the action, thread one of the long stock bolts into the hole at the bottom of the end cap and use it as a handle to turn the threaded end cap out of the spring tube. The barreled action should be installed in a mainspring compressor as this is done, and you’ll need to use a small socket to fit over the safety knob to put pressure on the end cap as you go.
The end cap is slowly being unscrewed from the spring tube. The threaded hole in the knurled section of the cap is where you thread in one of the stock bolts to start the end cap turning. After it gets going, you don’t need that bolt any longer.
The rifle I received for spare parts had been cocked for years, so the mainspring was under full tension all that time. I was extra careful when removing the end cap, but the spring was so collapsed from being compressed for so long that the end cap only came out of the gun by about an inch.
The cocking link on this rifle is a two-piece articulated one that doesn’t use a cocking shoe. Once the action is out of the stock, the cocking link will fall free from the spring tube as soon as there’s clearance. Since this rifle was cocked, it fell out immediately.
You may recall that I said my rifle was somewhat buzzy as well as being dry. Once it was apart, I could see it had never been lubricated from the factory. That was what was causing the cocking effort to be as hard as it was. I lubricated the mainspring with a product that’s no longer obtainable — Beeman’s Spring Gel. It was less aggressive than their Mainspring Damping Compound, which will subtract significant velocity from any spring gun to which it is applied. Spring Gel never worked well for me in the past, but I thought I’d give it another try, so I slathered it on the mainspring and on the outside of the spring guide. And that was the full extent of my lube job. I could see that the piston seal is a synthetic one, but I didn’t rub anything on it. It seemed oily enough from an earlier application of silicone chamber oil, and I thought I’d leave it that way.
The piston is a solid steel part that’s well-made. The piston seal is synthetic, and on this spare parts rifle the edge of the seal is chipped.
Then the rifle was assembled in reverse of disassembly, until we got to the trigger. I installed the small coiled spring and eased the trigger back into its proper place by inserting the other end of the coiled spring into the front of the sear. Then I aligned the holes and drove in the pin that holds the trigger in place.
Next, I installed the barreled action into the stock, taking extra care to “thread” the trigger blade through the trigger return spring that was still installed in the stock. This time, I knew about the spring; and even then I got it wrong a couple times before getting the spring into the right relationship with the return spring. Once that was done, the rifle cocked and functioned perfectly.
The trigger adjustment screw should not be tuned with the rifle disassembled; because if it’s turned too far out of adjustment, the rifle will not cock. That’s a safety measure in the design of the gun, but it also makes it difficult to assemble the rifle if you don’t know if the problem is where the adjustment screw is set or if you’re missing the correct positioning relationship of the trigger blade to the return spring.
Since I’d already chronographed this rifle before lubricating it, I had a good baseline against which to compare the now-completed rifle. I knew that the cocking effort had dropped from 35 lbs. to 21 lbs., which is a good indicator that the lube was doing its job, but what about performance out the muzzle?
Before the lube, Crosman Premier 7.9-grain pellets were averaging 589 f.p.s., with a spread from 586 to 593 f.p.s. After the lube, they averaged about the same 589 f.p.s., but the variation was much broader, going from a low of 577 f.p.s to a high of 614 f.p.s. That’s what you get following a lube tune, and it will soon settle back to where it was before. I don’t think there’s been any change in velocity at all.
The buzzy nature of the gun seems not to have changed at all, so I’m still having no luck with the now-obsolete Beeman Spring Gel. However, it did accomplish one thing — the reduction of excessive friction during cocking. That was the goal of the tune to begin with.
Now, I have a rifle that I can rely on, and I’ve scheduled at least one test for this rifle in the near future, so it’s good to have it back. I wrote this report because nowhere have I been able to read about the trigger return spring, and I wanted to document it for all who decide to tune this rifle in the future.