Archive for July 2008
by B.B. Pelletier
Before we begin, an announcement about an airgun show coming up. The Potomac Arms and Collectors gun show will be held in Frederick, Maryland, on September 13 & 14 at Elks Lodge #684. Hours are 9 a.m. to 5 p.m. on Saturday and 9 a.m. to 3 p.m. on Sunday. Entrance fee is $6, 6″ sales tables are $50 and 8′ tables are $60. Call 301-424-7988 and speak to Marv Freund to register. This is a combined gun and airgun show that draws a lot of Maryland, Virginia, West Virginia, Pennsylvania and Washington DC collectors. I’ve done well there with sales tables in the past. You’ll see some very nice collectible airguns at this show.
Today, I’m back to the Webley Raider 10, and we’ll look at velocity. Before we do, however, a report on the gun, itself. You’ll recall in part 1 that I said the gun’s action was very stiff and difficult to operate. That has carried over to the velocity test with only a minimum of loosening. The magazine fights you, making installation difficult, and the indexing is not precise. Several times I had to hand-index the next pellet.
The bolt continues to be overly stiff, though I do see some improvement. But moving it around its slot is as difficult as cocking a BSA Super 10 – another notoriously hard action to cycle.
Filling the gun, on the other hand, could not be easier. The probe fits the adapter on the end of the pump hose, and once the probe is greased with silicone diver’s grease, it slips into the rifle’s fill port easily.
Instructions were wrong
The rifle will accept a 3,000 psi fill, despite the manual specifying a 200-bar limit. The extra six bar gives an extra shot or two, which you’ll want because this rifle gets about 10 shots per fill. That’s not a misprint – I said 10 shots or a single clip. Let’s see how it does.
RWS Hobbys averaged 814 f.p.s., with a spread from 803 f.p.s. to 828. That works out to 17.51 foot-pounds.
Crosman Premiers went an average 796 f.p.s.. The spread was from 763 f.p.s. to 813. That’s an average energy of 20.12 foot-pounds. See how heavier pellets increase the energy in PCPs?
The 21-grain H&N Baracuda Match, which are very similar to Beeman Kodiaks, averaged 692 f.p.s. with a spread from 682 f.p.s. to a high of 699. That’s an average of 22.34 foot-pounds–the best of the three pellets. But let me show you the string and you will see what I mean about this being a 10-shot rifle. The gun was filled to 3,000 psi before starting.
That was for 10 shots. Looking at those last two velocities,* I can tell the gun is off the power curve and on the way down. But to show that to our newer readers more clearly, I loaded and shot three more pellets. Starting with shot 11, the velocities are:
A straight plummet, with little hope of recovering. If you buy this rifle, know its limitations.
The rifle is quiet for the power it projects. It sounds about like a Sheridan Blue Streak on 6-7 pumps. That’s the shrouded and baffled barrel at work.
Depending on which pellet you use, this gun ranges from 17.5 to 22+ foot-pounds. That’s a big spread. It also demonstrates the advantage of heavier pellets in a PCP. However, we still must shoot for accuracy to see which pellet to select.
A homework assignment!
All you budding pneumaticists have read quite a bit about pneumatics and PCPs this year. You just read about how a pneumatic valve works, and this rifle gave you a clear demonstration of the classic power curve of one. Here’s your assignment: Calculate the average velocity of 10 15.8-grain JSB Exact Jumbo pellets shot from this rifle on a 3,000 psi fill.
You can do this. It isn’t difficult. I will announce the answer in the next report.
Rick Klages had an unfortunate accident that bent the barrel of his R9 Goldfinger air rifle. He asked me for advice and was surprised when I told him to just bend it back. This is his story.
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by Rick Klages
It’s an overcast July 4th morning, and I’m working on adapting my artillery hold to a prone position. Being humid and hot outside has led me to perspire, and laying in the grass has made my hands slick. Compound this with my failure to remove my wedding band (titanium), and we have all the makings of a classic breakbarrel stupident. I was cocking my R9 Goldfinger while laying on my left side and palming the muzzlebrake instead of firmly grabbing it, when my hand slipped off. I was very near the end of the cocking stroke when the barrel snapped closed with nearly the full force of the mainspring.
So, I picked myself up and started to take stock of what just happened. Ok, no broken wood, good. Everything else looks normal. But when I took a few offhand shots at 50′, I realized there was a problem. The point of impact had moved 4″ upward. Now what do I do? I could call Beeman, but this was a holiday! Tomorrow was Saturday, and there was no way I could wait until Monday to work out my dilemma. The barrel doesn’t look bent. So, I asked B.B. what he thought. This was what he wrote back to me:
Your barrel is bent. It happens every time a breakbarrel slams shut. You are lucky the stock didn’t crack, too, as that often happens. You have to straighten the barrel again. A friend of mine does it all the time and he says the barrel will straighten easily, but will resist going past straight. You should be able to see the bend, which is located at the front of the base block, by looking through the barrel.
I was a bit incredulous at the suggestion I could simply bend it back, but B.B.’s instructions were simple:
Straighten the barrel by bending it in the opposite direction. It’s best to take the action out of the stock for this and support the action on a solid table. Muscle power, alone, is all you need to straighten an airgun barrel. As you bend it back, you can feel the steel “giving.” It sort of shudders as it returns to straight. Once straight, though, it does not want to bend farther, so the resistance increases.
I decided to give it a try. I removed the scope and took the action out of the stock. Using my sturdy kitchen table and a large, clean terrycloth towel as padding, I broke open the action. As I placed the compression tube/receiver on the towel, I applied downward pressure on the barrel. The spring cocking lever bottomed out in the action and the next thing I felt was a slight shudder. I used a fair amount of force. Pushing harder resulted in no other sensation of movement. Even though the rifle has a safety that automatically engages upon cocking, I made sure to keep clear of the naked trigger. It may be prudent to remove trigger units, if possible.
I then reassembled my R9. So how did it go? Here is my reply to B.B. after all was said and done:
It worked! I wouldn’t have believed it really. I didn’t think I could bend a steel rifle barrel without a press and since I don’t have Superman on speed dial I was skeptical. So I tried it. I will now add “Bends steel rifle barrels with bare hands” to my resume. Best of all my R9 is back to normal. Thanks for the advice.
by B.B. Pelletier
I got a request for this article last week from Manish in India and then another request to explain what is meant by the term valve lock, so I’ll deal with both subjects today.
There’s very little difference between the valve in a multi-pump pneumatic and a precharged pneumatic. Add air volume to a multi-pump reservoir and you can make the gun capable of multiple shots on a single fill of air. Then the only difference between that and a precharged gun would be the presence of the onboard pump. Therefore, the valve I will discuss applies equally to both types of pneumatics.
First, let’s look at a closed valve (graphic below). The reservoir is filled with compressed air that wants to get out, but the valve is blocking its way. Air pressure on the valve (red) presses it against the valve seat, which is a part of the valve body (black). The walls of the reservoir tube are also shown in black. A valve return spring inside the valve body also holds the valve shut, but with far less pressure than the air itself. The purpose of the return spring will be obvious in a moment.
When the gun fires, a weight called a striker or hammer is driven forward by spring pressure. It strikes the end of the valve stem (blue), driving it forward. When it goes, it takes the valve with it, opening small air passages around the valve stem that allow the pressurized air to escape.
What is “valve lock”?
Because the air in the reservoir exerts force on the valve, holding it closed, the higher the pressure, the more force it exerts. That force is balanced against the size of the valve, the weight of the striker and the strength of the striker spring. There’s a range of reservoir pressure in which the valve remains open long enough to pass the same amount of air, despite the fact that the air pressure inside the reservoir declines with every shot. When the air pressure is at the high end of the range, the valve remains open for a shorter time, but the higher pressure forces more air through the valve. When the air pressure drops, the valve remains open longer, allowing a greater length of time for air at lower pressure to flow through the valve. The same volume of air flows through the valve in both circumstances.
The result for a precharged pneumatic that gets many shots per charge is that even though the air pressure is dropping, the velocity remains more or less constant throughout this pressure range. For a multi-pump pneumatic, the pressure range doesn’t mean as much, except when the pressure goes too high. Then the valve cannot remain open long enough to exhaust all the air in the gun and there will still be air remaining for a second shot. Also, the shot the gun fires will be slower than normal, because less air is behind it.
The velocity will drop for both precharged pneumatics and multi-pumps when the air pressure goes above the range for which the valve was designed. The reason should be obvious – the valve closes before all the air needed for the shot can get out. This marks the beginning of valve lock. If the air pressure goes too high, the combined force of the striker and its spring will not be able to open the valve at all and there will be no shot. Now the gun is locked down by its own air pressure. The only remedy is to remove some of the pressure to drop the internal pressure down to a level at which the valve can open. Continued firing will drop the air pressure back down into the optimum operating range.
The performance curve
For this reason, using a chronograph with a precharged pneumatic allows the shooter to discover the exact pressure at which the valve operates best. And this decision can be left up to the shooter. If he wants more shots, he accepts a lower initial velocity (that comes from a higher initial pressure) and allows the rifle to climb in velocity, then fall back down to his established parameter. If he wants his shots to be as close in velocity as possible, he starts at a lower air pressure that gives him an initial velocity higher and closer to the highest velocity of which the rifle is capable. This is called the performance curve, and every non-regulated pneumatic rifle and pistol has it.
Some airguns, most notably those of Korean manufacture, are designed with sheer power in mind. Their valves are set to open at very high pressures, very close to valve lock. These guns will lock up if over-pressurized just a little, and they tend to have a steadily declining velocity instead of the curve described above. They can be modified to give longer strings of consistent shots, but the velocity at which they do it has to drop. So, a .22-caliber Career 707 might give the first five shots with .22-caliber Crosman Premiers that look like this:
If the rifle were tuned for more shots, the same first five Premiers might look like this:
This is what makes the AirForce Condor so remarkable. Not only does it deliver smashing power in the 60+ foot-pound range – it does so for the first 10 shots. And, if you’ll accept a velocity loss of 75 f.p.s., the first 20 shots are usable. No other smallbore air rifle has that kind of performance curve.
The Benjamin Discovery, which needs only 2,000 psi air to get identical performance to other rifles shooting with 3,000 psi, teaches us that air pressure, alone, doesn’t make velocity. The timing of the valve has far more to do with it than what’s inside the reservoir.
Those are the basics of pneumatic valves. They govern the gun’s performance, and they dictate the parameters under which the air pressure must be managed.
by B.B. Pelletier
Today, I’ll tell you how the new Leapers scope base for RWS Diana rifles installs, and give you some insight into what it was like to test this thing. The first thing you need to remember is that every RWS Diana air rifle has a different amount of droop. In general, the breakbarrels have more than the fixed barrels. I was fortunate to have on loan from Pyramyd Air an RWS Diana 34 Panther with a huge amount of droop. So much, in fact, that it was impossible to get on target at 20 yards by using just the scope’s internal adjustments. That was exactly the kind of rifle I needed to test this new base, because that was the worst problem of all…not a gun with a few inches of droop, but one with almost 21 inches at the most useful airgun range of 20 yards. If a base could compensate for a rifle like this one, it would work for most of the others that have less droop!
To put this into perspective, let’s look at a target I shot with the scope adjusted as high as it would go.
Don’t think that just because the target shows a 7-1/2″ drop that the rifle droops only that much. The scope was adjusted AS HIGH AS IT WOULD GO! If I centered the reticle, the pellet would be almost 21″ below the aimpoint.
The amount of droop was so great that the engineer at Leapers could hardly believe me. Anyone who has not actually experienced this before would find it hard to believe, but this is one of the reasons I wanted this new base so much. Over the years, I’ve had to talk many shooters through the workaround of scope shimming or convince them that adjustable mounts were what they needed. They always asked me how an airgun company could make a product with this much droop and not have something to correct it. To answer them I will point to the Hubble Space Telescope, which had vision problems for many years until corrected in orbit by NASA. If a telescope costing two billion dollars can have vision problems, I guess an air rifle can have barrel angle issues. Besides, Diana isn’t alone in this situation. Many other breakbarrels and some fixed barrels have a droop problem. It’s just that many more RWS Diana rifles are in use around the world and they all seem to droop in varying amounts but similar in that they all have it.
Speaking of fixed barrels, I did test a second RWS Diana rifle during the base development. I tested a .22-caliber RWS Diana 460 Magnum, which is a powerful underlever rifle. That rifle didn’t droop as much as the breakbarrel 34, but it still drooped more than some scopes can compensate. Other scopes would just be able to get on target with all their vertical adjustment used up. Although the one new mount would have worked for this rifle, Leapers decided to make a second base with less droop built in. They call it their 460 base. That gives you a choice of slope angles to fit any rifle out there.
We finally got it right
In part 2, I told you about all the prototyping Leapers did. I’ve left out the valuable lessons we learned in this testing because Leapers spent a great deal of their own money to get this product right. Others who try to copy them will probably run into the same problems we did and have to figure how to solve them.
By the fourth prototype, Leapers got the design and the slope right. All I had to do was mount the base, attach two rings and slap in a scope. The new base ended up with the vertical adjustment of the scope between the midpoint and the three-quarters point when the pellets were landing on target at 20 yards. That means the gun can be shot out to a great distance by using the internal scope adjustments because the base preserves most of their adjustment range.
Watch the video, if you can
The RWS Diana rifles have gone from being the most difficult rifles to scope to the easiest because of this new base. Paul Capello made a short video that shows how easy it is to now mount a scope. That video is on both the video page and on the product page with the new bases. Since some of you can’t watch videos, I’ll show you how to mount a scope using this new base. I will use the 34 Panther for my description and photos, but the procedure is exactly the same on all RWS Diana rifles and for either new base.
Loosen the screws on the sideplate of the Leapers base and slip it into the dovetails of the base on the rifle. Slide it back until the recoil shock shoulder contacts the front of the rifle’s base. It won’t move any farther. Snug it down. The base is installed. Time: about a minute, working slowly.
Next, install two Weaver rings in the slots of the Leapers base. Position them far enough apart for the scope you’re using and back far enough for good eye-relief when holding the rifle. Time: about two minutes, working slowly.
It’s best to use scope rings with four cap screws on all RWS Diana guns, so the caps are wide enough to provide maximum clamping pressure on the scope. Medium-height rings will be high enough for all scopes, because the Leapers base also raises the scope. Low rings will work with many scopes.
Last, install the scope in the normal fashion, using the instructions I provide in the scope-mounting article. Time: about 10 minutes, working slowly.
The new base takes care of two things:
- The barrel droop is corrected by the slope built into the base. Your scope will be on paper during sight-in and not too far from where it needs to be.
- The new base puts an end to scope base and ring movement. The recoil shock shoulder cannot be budged and the base slots and Weaver keys form a positive locking system for the rings.
If you’d like to print out directions, Leapers has a step-by-step sheet that is linked to both scope mount bases in the left column on the product page (under “Manual”).
The last report
This new base puts an end to barrel droop and all the problems associated with scope creep (broken big screw heads and narrow scope stop pins gouging scope bases on the rifle). It cuts the scope mounting time by two-thirds, and takes the operation from trial-and-error to plug-and-play. Now we can put our time to more profitable enterprises.
by B.B. Pelletier
This test is for DH and for all of you who like to hear about fine PCPs. Pyramyd Air sent me a .22-caliber Webley Raider 10 some time back and it was working its way to the front of the queue when DH asked about it. This is the 10-shot model, not the 2-shot rifle.
Like a carbine
The Raider 10 is light weight at 6.6 lbs. and short, at just 38 inches. It’s really more of a carbine than a full-sized rifle, but that should make the hunters happy. The metal is evenly finished in most places, with a few tool marks showing through on the receiver and some dull patches on the reservoir. The finish is a medium shine that’s brighter than matte, but not the deep black of some other airguns.
The beechwood stock is highly figured for beech and as attractive as many walnut stocks. It is fully ambidextrous, as well, though the bolt action is suited to right-handed shooters. The raised comb rolls to both sides of the butt. The cut-checkered pistol grip has a slight Wundhammer palm swell on the right side, but lefties will not find it bothersome.
The Raider 10 has a fully shrouded and baffled barrel, so I will be making comments on the noise signature. The power is not adjustable, and there are 10 pellets in each clip (which the owner’s manual calls a magazine).
Dealing with the fill adapter
I thought I’d do something new with this test. I’ll show you what I do when I receive a new PCP like this. The Benjamin Discovery and any AirForce rifle can be purchased ready to go, but no other PCP comes that way. Inside the package with the gun comes a fill adapter. In the case of a rifle from the UK, it’s threaded to screw into a 1/8″ British Standard Parallel Pipe fitting (BSPP). That’s a standard among UK PCPs. I own a Hill hand pump that has a hose that also has the other end of a 1/8″ BSPP fitting, so many folks would be tempted to just screw the two together. A lot of the time that would work, but sometimes not, so let me tell you what I do.
I wrap the threads of the quick-disconnect (probe-type) fill adapter with three wraps of Teflon tape (also known as plumber’s tape). If the seal in the hose is compromised in any way or even missing, this takes care of it. I wrap the tape in the direction opposite the one the adapter will be turning when I thread it into the hose.
The two o-rings on the adapter get a light coat of diver’s silicone grease. Please don’t write me and ask what you can substitute for diver’s silicone. Just get some. A quarter-ounce jar will last a lifetime.
The rifle also has a plug to seal the fill port when the adapter isn’t installed. It has an o-ring, as well, so I also greased it.
Pump her up!
The Raider 10 took 128 pump strokes to go from completely empty to 200 bar. By the way, when the Hill pump gauge says 200 bar the pressure gauge on the rifle reads 150. That’s a difference of 750 psi! It’s a huge difference, but be aware that it can happen. I will use the pump gauge because it has worked well in the past. When I get to velocity testing, I’ll refine the max fill number by watching the chronograph to determine where the gun comes up on the power band. Yes, you need a chronograph to do this and, yes, it’s worth it.
The bolt on this brand-new gun is incredibly hard to cycle! I had to strike it with the heel of my hand to get it to work. The clip didn’t always index properly in the beginning, but I think both of these things will even out as the rifle breaks in.
The two-stage trigger is adjustable for first-stage length, second-stage letoff and sear engagement. It seems nice enough as it comes from the box, so I’ll leave it as it is. There’s no safety on the rifle.
We’ll do velocity next.
by B.B. Pelletier
Let’s look at how the HW 55 SF performs, in terms of firing behavior and power. I told you about the rifle in the first two reports, but I didn’t dwell on how it shoots. First, the 55 is delightfully easy to cock. An effort of only 20 lbs. cocks the gun, due in great part to the length of the 18.5″ barrel. Because this is the rare SF model, there’s no barrel latch to contend with, but the flip side of that is, of course, a stronger breech detent holding the barrel shut. Years of fooling with Beeman Crow Magnums and Webley Patriots makes me slap the muzzle of every breakbarrel now to open it, so this is not a problem.
Firing the gun
The feel of firing this rifle is STRANGE! You hear the sound of faint spring buzzing but you don’t really feel it! Though the rifle is only 8 lbs. (very light for a target rifle), the cocking slot in the bottom of the forearm is abbreviated because of the two-piece articulated cocking lever. Robert Law made a big deal of this in his catalog, and I’m finding that it’s really true. He said the more solid forearm attenuated most of the shooting vibrations, resulting in a smoother-feeling rifle, and I have to agree. I have owned or had other HW 55 rifles for testing, but I cannot ever remember this trait. Perhaps it’s due to the last tuneup it had.
You’ve learned in this series that this HW 55 is made on an HW 50 spring tube and should perform like an HW 50. Except that the HW 50 we know today is not the same gun as the HW 50 of the 1960s, when this one was made. The current model is actually based on a different spring tube and is a more powerful airgun. The HW 50 of the 1960s had leather piston and breech seals, a smaller spring tube and was a 700 f.p.s. rifle in .177 caliber.
While good for sporting purposes, 700 f.p.s. is too fast for a target rifle. It doesn’t necessarily make the rifle less accurate; but if you don’t need the speed, why bother with the extra pounds of cocking effort? To make the 55SF, Weihrauch installed a weaker mainspring. This particular rifle has been tuned at least twice since it was built, so the original mainspring is probably no longer in the gun. I was concerned to see just how powerful it is, hoping that the last tuner hadn’t tried to hot-rod it.
I tried RWS Hobbys first and got an average of 631 f.p.s. The range was quite large – from 614 to 652, which leads me to believe RWS Hobbys are not right for this airgun.
I have H&N Match pellets, but only the light ones for pistols. This is one time where it matters. The average of 622 f.p.s. is a little too brisk, though the range was much tighter. Just 19 f.p.s separated the low of 614 f.p.s. from the high of 633. Much better performance, but still on the hot side.
RWS Meisterkugeln pellets dropped the average to a more sedate 543 f.p.s. The spread was from 536 to 554 or just 18 f.p.s. The tightest spread of the three pellets.
The rifle could stand to go a little faster, but 542 with a qualified rifle pellet like the Meisterkugeln isn’t bad. Today’s pneumatics would only be at 575 or so. In the mid-1960s, target airguns were in a bit of a velocity race that ended abruptly in the 1970s. Target rifles were pushing pellets out at 640-650 f.p.s., because the competitors had yet to be heard. When they were, velocities dropped back below 600 f.p.s., where they remain today.
What’s it like to own and shoot a vintage 10-meter rifle like this one? I have owned a few vintage airguns that were not unlike owning a Stanley Steamer. Once they get going, the statistics can be impressive but you wouldn’t want to rely on them all the time. This rifle is not like that. While no one would confuse it with a world-class target rifle, it’s still good enough for informal target shooting and the occasional grudge match. It has no funny quirks or surprising traits, in fact just the opposite. It’s easy to cock, has a trigger too light to measure and a firing behavior that endears itself to every new shooter. It quickly becomes a “go-to” rifle if you give it half a chance.
We have one more report coming on accuracy, unless there’s else something you want to know that I’ve overlooked.
Introduction by B.B. Pelletier
Wayne Burns is a new reader of this blog, though he’s been an airgunner most of his life. But he’s learning about new kinds of airguns here, and sharing those experiences with us. Today, he tells us about a modification he made to his Benjamin Discovery rifle.
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Discovery barrel – to glue or not to glue
by Wayne Burns
I’m not an experienced airgunner, but I got the bug bad . So bad, in fact, that I thought other babyboomers must be getting it, too. So, I’ve been testing low- to mid-priced air rifles with the intent of opening an air rifle range in the near future.
When I read B.B.’s reviews of the Benjamin Discovery, a gun he helped design, I got excited like a million others and got in my order at Pyramyd Air. The wait was worth it. I must have been one of the first to get one, because my review at PA (without the pump) is at the bottom of the list now.
In the beginning, I really didn’t notice that the barrel could flex back and forth with easy finger pressure. After about 2,000 very fun and mostly accurate shots, I noticed the flex and was sort of outraged. Then, I said to myself, “It’s been shooting fine, the air tank protects the barrel from getting wacked, and light gauge material keeps it low cost and light weight.” BUT how can it be as accurate as it could be, if the barrel flexes? Without much thought, I removed the fill cap and put a couple of drops of Super Glue right where the barrel touches the air tank near the fill cap (being sure to not get glue where the cap goes on). I let it dry overnight, and the next day no flex.
I promptly complained to B.B. about the “flexing” barrel in this forum, (I should have complained before the gluing) and B.B.s’ polite reply was:
I have to caution others to not Super Glue the barrel to the reservoir. The reservoir moves as air is exhausted and if the barrel is attached, it will walk as the pressure changes.
What did I do?
I wrote back and said something like, “It seems to still shoot as accurate as before.”
B.B. replied, “That’s what counts.”
But, I wasn’t sure. Because, as the pressure in the tank drops below about 1,200 psi, the pellets hit lower because of lower velocity. But B.B.’s comment made me think that maybe they were dropping because the air tank was pulling down on the barrel as the pressure went down.
I told B.B., “My brother-in-law, Randy, has a Discovery I gave him for his birthday that is not glued.” (He waited to see what happened to mine.) “Maybe I could do some sort of test.” B.B. said, “Why not make it a blog?” So, here we are.
At what pressure do pellets start dropping from lack of velocity? When we know that, we can see if the pellets from glued or unglued barrels are dropping differently. I thought it was after about 30 or 35 shots in my rifle when I fill it to 2,200 psi.
My test was to have Randy and me shoot each rifle down to the red sector on the gauge with the same type pellet.
First attempts at testing failed due to human error. It’s too hard to know what is human factor, pellet factor or scope movement. All three proved to be problems.
So, I bought two Benchmaster rifle rests at a local shop. They eliminated the human factor, pretty much.
Next, which pellet?
While testing for the best pellet, we found that the 4-16×50 Leapers scope on my rifle would not stay adjusted, so we changed to the rock-solid 3-9×40 CenterPoint on each rifle. They’re not as great for field target, but fine for this indoor test at 60 feet.
After much testing, we found that the 15.8-grain .22 cal JBS Exact Jumbo pellets were just a little better than the 14.3-grain Crosman Premiers. Premiers average 791 fps, and the heavier JBS was 773 fps.
First, we shot the non-glued Discovery to find out at what point it dropped from lack of pressure. Then, how much the glued Discovery dropped at the same point on the pressure gauge. Not very high tech, but that’s all I could think of.
What the heck?
Randy filled to 2,200 psi and had a problem. This is a problem some other novice airgunners might run into with the Discovery, so, at this point, I will just show you my email to B.B. (Tom Gaylord).
Randy and I are testing tonight, but the crony tests I did earlier today – filling on the scuba tank that was down to 2,000 lbs. – are puzzling. The crony shows that when the we fill to 2,000 psi, it takes about 8 or 12 shots to get to peak velocity. That seems strange. I would think that the more pressure in the tank, the more f.p.s. But the strings on the crony for the RWS Superpoint start at 786 and climb pretty steady up to 821 on the 13th shot, then – 823, 815, 820, 820, 817, 820, 822, 820, 814, 811, 810,796,804,795,786, 782 and 780, where I stopped.
Randy filled his rifle from the new tank, so it got filled to about 2,200 psi. He started the test having not shot his Discovery for a few weeks, so when the first shots were low, he adjusted his scope accordingly and found the center for awhile. Then his shots started going higher. He adjusted the scope again to the center and stayed on target (see target number 4). By this time, he had fired about 45 shots. Then his pressure continued to drop and he got a great 6 shot group 1-1/2″ low. Then the needle on the gauge went into the the red and his next shot dropped a full 3″.
He didn’t tell me what he was doing. When I heard, I showed him the crony test from earlier. It matched his results. We both wondered why it has less power and shoots slower with more pressure in the tank. Here are some photos from that first test.
This makes our test more difficult, don’t you think? HELP!
Tom wrote back:
You are encountering valve lock. A valve is balanced to the pressure at which it operates. When I designed the Discovery, I told Crosman that an airgun could be just as powerful at 1,800 psi as it was at 3,000 psi. They didn’t believe me, but when they built the first prototype, they discovered that it worked.
The pressure at which a valve operates can be changed by changing the spring rate of the valve return spring or by changing the valve diameter or by changing the valve seat angle or by changing the weight of the striker or by changing the striker spring rate or by changing the valve stem height. Any of those six things can change how a valve works.
Even YOU are over-pressurizing your gun by filling to 2000. The proper fill level is the pressure at which the first shot comes out at full power.
Shoot the gun until the velocity rises to what you consider to be the ideal velocity. That sounds like 820 for your rifle. Then stop shooting and try to fill the gun at that point. Note the pressure at which the gun begins accepting air. I’m guessing your rifle will like a fill of 1,800 psi. They will each differ a little, so don’t go by the 2000 psi on the gauge. Learn the fill your rifle likes, then fill to that level and stop.
Why doesn’t more pressure make the pellet go faster? Well, answer this: why doesn’t more gas in your car’s gas tank make the car go faster?
Because a car doesn’t work that way, you say. Well, neither does an airgun. There is a range of pressure at which the valve opens to the maximum and stays open the longest time. Within that range you will get the maximum velocity that valve is capable of delivering. Tests have shown that the Discovery gets 21-26 shots in a tight velocity spread. Some people will shoot up to 35 shots because they will accept a larger velocity spread. A person shooting groups at 50 yards will notice a POI shift resulting from a velocity variation sooner than a person shooting groups at 10 yards.
Each PCP is unique and needs to be tested to determine the max fill pressure. It is impossible to manufacture two PCPs that work exactly the same, just as it’s impossible to manufacture two cars that have the same top speed. You can adjust and modify two guns to perform similarly, but even then you cannot get them to be exactly identical.
You mention opening a scuba tank’s valve when the tank pressure gets to 2100 psi. You think that is okay. I shudder, because you are overfilling the gun. Think of going to the gas station and, after your car’s tank is full, you pump the rest of the gas out on the ground, so the number on the pump reaches an even number of gallons. That’s what you are doing when you fill like that.
Stop looking at the numbers and start learning your rifle’s individual performance characteristics.
We had to start over, initially filling until the Discovery gauge reached about 1,800 psi. With the guns filled to 1,800 psi and shooting off the bench rests, we shot a few more tanks of air – only trying for 30 to 35 shots.
In this first test, the non-glued barrel had the best 35-shot group. We found it better to shoot groups of five at different targets, so we could see more detail. Notice that when you shoot over and over at the same spot on a thick board, it will break…and that’s a 2×6!
We eventually found that our guns did best starting at 1,700 psi, and going for only 20 or 25 shots if we didn’t want to change our aimpoint. If you’re willing to adjust for the different impact point that comes from a lower velocity (aiming high for the first 10 shots or so, then right on for 20 to 25 shots, then high for the last 10 shots or so), you can get 40 or 50 shots on a tank filled to 2,000. It’s not so hard to learn how to adjust your aim, and worth it, if you’re hunting. For shots over 30 yds., I have to start aiming high anyway.
In the second test, with both guns filled to only 1,700 psi, the gun with the glued barrel did a little better than the one that wasn’t glued. I noticed that the chrony and the accuracy say that shots 1 and 20 are close to the same when starting at 1,700 lbs. Keep in mind that you still have 10 or 12 more shots if you want to aim high, but they still have enough wallop to kill a starling at 25 yds.
If it really bothers you (like it did me), it probably won’t hurt to glue your barrel. It could be that the cheap super glue I bought flexes enough to give with the movement of the tank. Or, the air tank is strong enough to not flex as the internal pressure drops. [Note: It isn't - Ed.] By far, the more important factor for accuracy in the Discovery is the proper fill pressure. Then get to know where the valve lock occurs and how it affects accuracy in your particular gun…if you want to stretch the number of shots you get from a fill.
Another fix, is to add another barrel band, or move the one closer to the end if you think the flex is a problem at all.