Posts Tagged ‘maintenance’
by Tom Gaylord, a.k.a. B.B. Pelletier
This blog is for those who are new to shooting and to airguns. Sometimes, we have to address the basics, and that’s what I’m going to do today. I’m inviting the veteran shooters to chime in with their own ideas of what the new airgunner should avoid.
For reasons I cannot fathom, new shooters think they need to clean their airguns even more than firearms are cleaned. I know people who never clean their .22 rimfires until they start to malfunction, yet these same people don’t hesitate to take a bore brush to the barrel of their favorite air rifle every chance they get. It isn’t necessary to clean an airgun barrel that often, and it actually exposes it to possible damage from the cleaning process gone wrong.
Why do we clean a gun?
Historically, guns used what we now call black powder, whose residue both attracts moisture and then turns it into sulphuric acid. It begins to do this in less than 24 hours following shooting, so cleaning was/is essential if the bore was to be preserved. Later, when smokeless powders were developed, the early primers that ignited them contained compounds that were just as corrosive to the bore as black powder residue. A great many .22 rimfire rifles have lost all their rifling from the combined activities of this primer-based corrosion, coupled with over-zealous cleaning.
More recently, shooters have discovered that the jacketed bullets of centerfire cartridges will quickly foul barrels with metal deposits. While this doesn’t corrode the metal, it does fill the rifling grooves with jacket metal until all hope of accuracy is lost. So, the metal fouling has to be removed with a combination of chemical and mechanical action.
The modern .22 rimfire, in sharp contrast, uses clean-burning powder, clean priming and shoots clean lead bullets at low velocities. Nothing in its makeup or operation requires frequent cleaning. Those who shoot .22s can get away with not cleaning their guns for many hundreds and even thousands of rounds. Eventually, there will be a buildup of powder fouling even in these clean guns, but the contrast with centerfire guns is vivid.
Finally, there are the airguns. They neither burn powder nor use primers, so there’s no residue. They shoot at low velocities (compared to many firearms) and use clean lead pellets, so there’s little metal fouling. Only with some of the more powerful airguns do the velocities get fast enough to scrape off some lead from the pellets. And some barrels seem more prone to scrape off lead than others. That, alone, is the sole cause for buildup in an airgun.
In contrast to a firearm, an airgun can be fired tens of thousands of times between cleanings…and some lower-velocity airguns may never need cleaning at all. Those with brass or bronze barrels are entirely impervious to cleaning requirements.
The time to clean your airgun is when the accuracy falls off, not before. Do not clean an airgun barrel on a regular schedule — they simply don’t need it.
2. Disassembly without a plan
I’ve done this and so have many of you. The gun isn’t working right, so we take it apart to find out why. Then, we haven’t got a clue how to get it back together. That results in a basket case of parts that somebody else will be able to buy for a song. Don’t create bargains for others! Before you take an airgun apart, give some thought to what it takes to put it together again.
The way to do this is to first research the gun on the internet, to see if there are any disassembly or assembly problems. If there are known issues with a gun, there should be plenty of information on the internet.
Another thing to look for is if any special tools or equipment are needed. With spring guns, you usually need a mainspring compressor to safely disassemble and assemble the gun. And if you’re disassembling a BB gun like a Daisy Red Ryder, you need to make a special fixture to hold the gun while the mainspring is compressed and parts are removed. Unless you have three arms, this fixture is absolutely necessary.
Then, there are guns that are assembled during manufacture in ways that make them almost impossible to repair. One good example of this is the barrel of a Benjamin 392, which is soldered onto the pump tube at the factory. If the solder joint is ever broken, it’s next to impossible to repair. That’s because the joint is very long and is difficult to keep an even heat on the entire joint at the same time. The solder flows in some places, but clots in others. When you move the heat to the places where it’s clotted, you lose the solder that flowed before.
Don’t attempt repairs or modifications unless you know you can do the entire job. Better to spend some money to get the job done right by an airgunsmith than to charge in and break or lose some irreplaceable part.
Some of the new owners’ manuals tell people to oil the compression chamber on a frequent schedule. While oiling was appropriate for guns with leather piston seals, the newer synthetic seals don’t need nearly as much. Over-oiling causes detonations that can damage the gun if they’re allowed to continue; and once they start, there’s almost no way to get them to stop. All spring guns diesel; but when they go off with a loud “bang,” that puts a strain on the mechanism.
I always like to err on the side of under-oiling because all that does is make noise during cocking. Over-oiling causes problems, though, and in extreme cases the airgun must be disassembled and dried out.
There are places to oil besides the compression chamber. Linkages need a drop every now and then, and the wood parts can always benefit from a Ballistol wipedown.
The other place oiling is necessary is on the tip of each fresh CO2 cartridge before it is pierced. The best oil for this job is Crosman Pellgunoil, and a CO2 shooter needs to always have some on hand. The oil is blown through the gun’s valve when the cartridge is pierced; and it gets on all the sealing surfaces, making a tight seal against gas loss. It’s the No. 1 maintenance action a CO2 gunner can take, and you absolutely cannot overdo it.
So, what happens when an airgun is not oiled enough? It makes noises to tell you. Spring-piston guns will honk like a goose when they’re cocked if there isn’t enough oil on the piston seal. Mainsprings will crack and crinch when cocked as they slip their coils when they don’t have enough oil. And the fork that the breech sits in will become shiny if there isn’t enough grease between it and the breech. Also, the cocking effort will increase dramatically.
CO2 and pneumatic guns will develop slow leaks when they need oil. Their seals cannot do the job without a thin film of oil on all their surfaces. But if the gun is holding air, stop with the oil — except in the case of CO2 guns, as noted before.
This fault is as old as the hills and is a classic mistake a newcomer will make. If 10 pump strokes give X amount of power, shouldn’t 15 pump strokes give 1.5X? No! In fact, they do just the opposite. Over-pump a pneumatic or overfill it from a scuba tank, and the velocity takes a nosedive. It will drop all the way to zero, at which point the valve is locked shut by the excessive pressure in the gun. Imagine a door being held shut by several strong people. No amount of pushing will open it. You have to wait for some of the people to leave or, in the case of the gun, for some of the internal pressure to drop. That can take weeks and even months!
A pneumatic gun is designed to work within a certain pressure margin. Too little pressure and the power drops. Too much pressure and the power drops. Remember it this way — putting more gas into a car’s tank will not make it go any faster.
With CO2, you don’t have to add pressure; and in fact, there’s no straightforward way to do it. If you were to increase the gas pressure somehow, all that would happen is more gas would condense to liquid. The pressure would remain the same. But if the outside temperature should go up, the gas pressure will increase as well because the gas pressure is dependent on temperature. Operate your CO2 guns when the temperature is between about 60 degrees and 90 degrees F. And don’t leave a CO2 gun lying in the direct sun, even on a relatively cool day, because the gun will absorb the sun’s heat and will go into valve lock.
There you go — 5 simple things to remember about airguns and their operation. Perhaps our readers can suggest more?
by Tom Gaylord, a.k.a. B.B. Pelletier
Let’s begin testing the effects of oiling pellets. There are numerous ways to approach this issue, and I have to pick one at a time and limit the test to just that. But I think as long as I’m testing one aspect, I ought to test it thoroughly so someone can’t come back and second-guess me later in the report.
So, today I’ll test with one rifle, and the next time I’ll test with another. What I won’t do is test with each different brand of airgun, just to see what will happen. If a powerful gas spring rifle performs in a certain way, I’ll assume that all powerful gas spring rifles are going to do the same. If the difference between dry pellets and oiled pellets is close, I may do additional testing; but if there’s clear separation, I’ll accept that as the way it works.
What am I testing?
The question that started this experiment was, “How much faster will oiled pellets shoot than those that are not oiled?” One reader has asked me to also test this downrange because he wonders if a thin coat of oil changes the laminar flow of air around a pellet. I may get to that at some point, but for the present I’m just concerned with muzzle velocity because all pellets slow down after they exit the muzzle — oiled or not.
I suppose this needs to be tested in all three powerplant types, but today I’m testing it in a spring-piston powerplant. Today’s gun is a weak powerplant, so next time I’ll test it in a more powerful gun.
I’m using an HW55 SF target rifle to test three pellets. This rifle is a variation of the old HW50 rifle, so it shoots in the 600-650 f.p.s. region with lead pellets.
Since oiled pellets will leave a film in the bore, I tested all pellets dry first, and then tested the oiled pellets afterwards. Before the first test shot with oiled pellets, I fired two pellets to condition the bore. That turned out not to be enough, but I’ll come to that later.
I’ll test the three major pellet shapes in this test. They’re the wadcutter, dome and pointed head. There are other shapes, like hollowpoints, but they’re based on one of these three main shapes, so this is all I’m testing.
How I oil pellets
I oil pellets in the following manner. A foam liner is placed in the bottom of a pellet tin, and 20 drops of Whiscombe Honey are dropped onto the foam. Then, a single layer of pellets is spread on the foam, and the tin is rolled around. I shake the tin lightly to move the pellets around…but not enough to damage them. Whatever oil transfers to the pellet is all the oil it gets. I’ve been doing this for many years and it works well.
The pellets end up with a very light and uniform coat of oil. When I handle them the tips of my fingers become oily, but I can’t see any oil on the pellets. Other people use more oil than I do, but this is what I am testing.
Whiscombe Honey is a mixture of two-thirds Hoppes Gun Oil (not Number 9 bore cleaner!) and one-third STP Engine Treatment, by volume. Shake the mixture until is takes on a light yellow color. It will look like thin honey, hence the name. This mixture should not detonate easily in a spring gun.
Test one — dry pellets
Crosman Premier 7.9-grain pellets were the domes I tested. The average velocity for dry Premiers was 606 f.p.s., with a low of 577 and a high of 616. So, the spread was 39 f.p.s. The average muzzle energy was 6.44 foot-pounds.
For wadcutters, I tested Gamo Match pellets. The average for dry pellets was 652 f.p.s., with a low of 640 and a high of 663 f.p.s. The spread was 17 f.p.s. The average energy was 7.14 foot-pounds.
H&N Neue Spitzkugel
The pointed pellet I selected was the H&N Neue Spitzgugel. When shot dry, they averaged 601 f.p.s., with a low of 585 and a high of 620 f.p.s. The spread was 34 f.p.s. The average muzzle energy was 6.81 foot-pounds at the muzzle.
Now, I shot two oiled pellets through the bore to condition it and began the test.
Oiled Crosman Premiers
Oiled 7.9-grain Premiers averaged 591 f.p.s., but the spread went from a low of 545 to a high of 612 f.p.s. That’s a spread of 67 .p.s. The average energy for oiled pellets was 6.13 foot-pounds. I did notice the pellets were going faster at the end of the shot string, so I thought I might come back to them after testing the other pellets.
Oiled Gamo Match pellets
The oiled wadcutters averaged 658 f.p.s. — a slight gain over the dry pellets. But the real news was the spread, which went from a low of 651 to a high of 663 f.p.s. Instead of a 17 f.p.s. for the dry pellets, the oiled pellets gave a spread of just 12 f.p.s. That’s too close to draw any conclusions, but it’s interesting. The average energy with the oiled pellets was 7.27 foot-pounds. So, with the oiled pellets, the velocity went up — along with the energy — and the shot-to-shot variance went down.
Oiled H&N Neue Spitzkugel
Oiled Spitzkugels averaged 609 f.p.s. — which was a small increase over the same pellet when dry. The average energy was 6.99 foot-pounds. The spread went from 585 to 620 f.p.s, which was identical for the same pellet dry. Velocity and energy were both up slightly from dry pellets, and the shot-to-shot variance remained the same.
By now, it’s obvious that the bore needed more than two shots to condition it, so I retested the oiled Crosman Premiers. The second time the oiled pellets averaged 604 f.p.s., which is just 2 f.p.s. slower than the same pellets dry. But the spread that was 67 f.p.s. on the first test of oiled pellets and 39 f.p.s. with dry Premiers now went from a low of 594 to a high of 613 f.p.s. — a much tighter 19 f.p.s. total. The average energy was 6.40 foot-pounds.
From this test, I observed that these three pellets either remained at the same velocity or increased very slightly from the light oiling I gave them. In two of the three cases, the velocity spread got tighter when the pellets were oiled.
I further observed that it’s necessary to condition a bore with oiled pellets before doing any testing. As a minimum, I would say that 20 oiled pellets should be fired before testing.
These are very small differences from oiling; and although I can’t draw any conclusions yet, I would think that such a small change is not enough to matter. It hardly seems worth doing at this point. However, there’s still a test to be done in a powerful airgun. Until we see those results, I think it’s too soon to say anything for sure.
Although the question that drove this test was how much faster oiling pellets makes them shoot, I think we still have to take accuracy into account before forming any opinions.
And now for something completely different
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by Tom Gaylord, a.k.a. B.B. Pelletier
This report will be lengthy because I want to test several aspects of oiling pellets. For starters, I want to test it with spring guns, PCPs and CO2 guns just to get a complete picture of what, if anything, oiling pellets is doing in each of those powerplants. I’m interested in velocity because of the question that spawned this blog, but accuracy might also be interesting to test.
We received this question in the following form. I will paraphrase, but this is the gist of it, “How much faster do pellets go when they are oiled?” That question came in on one of our social networks and was referred to me for an answer. Well, you know me! Give me a topic and I turn it into a week’s worth of blogs. But this question really begged for the full treatment because there’s so much to cover.
When I got interested in shooting airguns as an adult in the middle 1970s, the question of oiling pellets wasn’t around (as far as I know). In talking with the late Rodney Boyce, I learned that the oiling question really came to a head when PCPs first started being used in the early 1980s. A PCP shoots very dry air, and their barrels are made from steel; so, at the higher velocities, they tend to get leaded bores. Some shooters were also oiling pellets for their spring guns; but a lot of the time they did it because they washed the pellets, thinking the black compound on them was dirt. In fact, it was anti-oxidant to keep the pellets from turning to white dust. Had they just left the pellets alone, they wouldn’t have oxidized.
In defense of the spring-gun guys who washed their pellets, though, some brands did have a lot of lead swarf (flakes of lead from the manufacturing process) inside some of the pellets, and vigorous washing did remove it. But then the pellets needed to be oiled again, or they would quickly oxidize.
Why we oil pellets
We oil pellets for two reasons. The first is to prevent the oxidation of the lead after washing. The second is to reduce the leading of the bore, though this is principally a PCP problem. Other pneumatics either shoot too slowly or they have brass or bronze barrels that do not allow the lead to attach itself, so they do not lead up.
Do oiled pellets shoot faster?
That was the question that started this report. I’ve tested this in the past and found that with a PCP shooting .177 pellets at 850-900 f.p.s., oiled pellets went slower, not faster. But that was just one test, and I don’t want to say what oiling will do for other guns until I do some more testing.
I’ll tell you this — oiling pellets became such a hot topic in the late ’90s that people were swapping their favorite secret formulas on the internet. And I know one UK company that sells an oil for pellets that they still claim gives increased velocity. Well, that’s too good to pass up, so I’ll test some of their oil in this test.
Not just oil
Don’t think that oil is the only thing people put on pellets. I remember lengthy discussions of how to apply a thin even coat of wax on pellets. Then, the topic shifted to what kind of wax to use! One guy went so far as to specify a high-tech boat hull compound called Bo-Shield for his pellets. When he talked about it his eyes got that faraway stare, as though he was transcending the real world and entering the spirit world.
What I will test
The first thing I want to do — have to do, in my mind — is test what the application of oil does to the velocity of pellets. Okay, that opens about 10 worm cans, right there:
What constitutes “an application of oil”? (I have seen paragraphs of instructions telling you how to know if the application of oil has been enough or if you need more.)
Am I testing this on lightweight pellets? Heavy pellets?
Do I test a powerful springer as well as a lower-powered springer?
Do I also test this on a precharged pneumatic?
A powerful PCP and a lower-powered PCP?
What about testing on a CO2 gun?
And on and on….
I think the best approach is to ask the question: Why do we oil pellets and who does it? We know that people who wash pellets also oil them, and we know that PCP users oil them; so that includes all the categories above. I don’t see a need to go to the extremes with this test. I’m not HP White Labs, and this isn’t a burning consumer question. If the findings suggest further testing, I could decide at that point?
What about the possible side effects?
Will oiling a pellet cause extra dieseling? Maybe. Is that what’s behind those flimflam salesmen who claim that oiled pellets go faster than dry pellets? I don’t know for certain; but as long as I’m going down the path, this is something I want to look at. Obviously, we’re talking only about powerful spring guns.
Does oiling affect accuracy?
I don’t know, but it seems we ought to find out. This gives me another excuse to unlimber my R8…so, hurrah!
Have I forgotten anything?
You tell me if I’ve overlooked any test that ought to be conducted. This isn’t a guessing game or a creativity contest, so please tell me only things that really matter to you.
by Tom Gaylord, a.k.a. B.B. Pelletier
El Gamo 68 is a futuristic breakbarrel from the past.
I last reported on this rifle on August 8 of last year. And that was Part 5! I had just tuned the rifle with a new mainspring and proper lubricants and was wondering what the changes would be. I was ready to report on it several months ago when I discovered that it wouldn’t cock. After fiddling with the trigger adjustments awhile with no success, I set it aside and moved on — thinking that the gun would need to be disassembled.
I disassembled it last week and discovered there was nothing wrong! The sear was working properly, or at least it seemed to be when I played with it as the gun was disassembled. I relubricated everything and put it all back together and was going to write Monday’s report on it. But the trigger still didn’t work! ARRGH!
This time, I remembered that when I got the gun the trigger was also a bit iffy, so I fiddled with the adjustments WAY outside the normal realm and, presto! I got it working again. Oh, it took a couple hours and there were some accidental discharges when the barrel was closed (direct sear!), but I solved all that by giving the sear way more contact than it needs.
Now the trigger releases at about 12 lbs., but at least it’s safe. Today, I’ll share with you how the tuned gun does at 25 yards — heavy trigger and all.
One other thing I did to the rifle was lubricate the leather piston seal with 10 drops of 3-in-One oil, leaving the rifle standing on its butt for two days afterward. The oil was allowed to slowly soak into the leather, which it did, but to protect the carpet and walls (Edith–Are you listening?) I put a long drop cloth in front of the rifle when I shot it.
Today’s test is a deviation from my normal pattern. I’ve tuned this gun and not yet reported the new velocities, and yet here I am shooting for accuracy. I decided to do it that way; and if I got good results, I would test the velocity next. I’m not changing the usual way of doing things — this is just an exception.
The first pellet I tested was the RWS Hobby. I chose it for its light weight and because it’s often accurate in lower-powered spring rifles and pistols. Sitting 25 yards from the target, I have to admit that I was wondering if the rifle had enough power to hit that target — let alone shoot a decent group.
Five of the first 10 pellets were detonations from the oiled piston seal. And the smell of burning oil was in the air. The Hobbys landed in a vertical group that was pleasingly tight from side to side. I was prepared to blame the verticality on the dieseling, but the truth is, that wasn’t the problem. The gun just doesn’t want to shoot Hobbys at 25 yards. That’s not too surprising since 25 yards is about the maximum distance for any wadcutter pellets, in my experience.
Air Arms Falcon
The second pellet I tested was the Air Arms Falcon, a 7.3-grain dome that’s often accurate in spring rifles. I used the spotting scope only on the first shot, which was a detonation, to make sure it was on the paper. There were 4 detonations in the 10 shots. I didn’t look at the target again until I walked down to change it. Boy, was I surprised by what I saw! To paraphrase Crocodile Dundee, “Now, THAT’S a group!” For open sights at 25 yards and 65-year-old-eyes, it ain’t too bad!
Remember, I’m shooting 10 shots — not 5. So this kind of group really proves the rifle can shoot. It also proves this old man can still hit things when the rifle does its part! So much for the problems of the droopers and gas springs! I needed this validation after some of the disappointing tests I’ve done recently.
The heavy trigger apparently is not causing much of a problem for me. I think that’s because the rifle is rested. If I were shooting offhand, I’d want a lighter trigger-pull.
JSB Exact RS
Next, I tried JSB Exact RS pellets. This is another 7.3-grain dome from JSB (JSB also makes Air Arms Pellets) and is very often accurate in many different airguns. And this is one of them. The group is slightly larger than the Falcon group, but the two are so similar that I would call it a tie.
The last pellet I tried was the RWS Superdome, which often does well in lower-powered spring rifles. This time, however, it didn’t. Ten pellets produced a 1.765-inch group. It didn’t disappoint me, though, because the Falcon and JSB RS groups looked that much better. It showed that the earlier Hobby group wasn’t just a fluke of bad luck — the gun simply likes what it likes.
This test was calming for me. It was slower than many of the tests I’ve run in the past month, and the results were more based on me as a shooter rather than on the equipment. I find that I like that a lot!
The El Gamo 68 XP is operating well right now, except for the heavy trigger that I’ll probably keep just as it is for a while. The tuned powerplant is now smoother with less of a jolt. I noticed in this test that each pellet has a firing characteristic of its own. The two JSB pellets were definitely the smoothest of the four tested, and the Hobbys were the roughest.
This is such an odd airgun, with the fat heavy butt and no forearm to hold. Yet, it shoots like a thoroughbred. With the new tune, it cocks smoothly and just feels good to shoot — I don’t have any better way of describing it. I wish you could all try one, but since you can’t, I will, again, recommend the Air Venturi Bronco, which is the closest thing still being made today.
by B.B. Pelletier
Last week, our new reader, Cantec, mentioned that several gentlemen were advising the use of corn oil for lubricating the compression chambers of spring-piston airguns. I know exactly where this recommendation came from and how it should be viewed, and I wanted to share this with you today.
Yes, I’m talking about common corn-based cooking oil. Wesson oil is the most popular brand here in the U.S. Why would anyone recommend using corn oil in a spring-piston airgun? I want you to know the entire truth so you don’t make any serious mistakes with your guns.
Good old corn oil that’s most often used for cooking has also been used to lubricate some spring-piston airguns.
In my role as a firearms enthusiast, I used to put WD-40 on all my guns. It smells so good and guns always look so nice after they have been wiped down with it. So, when the Army sent me to Germany for four years, I sprayed WD-40 on all my guns before storing them in my mother’s attic, thinking I was protecting them against the ravages of time. What happened, instead, was that the WD-40 dried out and left every gun covered with a thick coating of yellowish residue that proved nearly impossible to remove. Only more WD-40 would dissolve it, and in one case the silver plating on my collectible second generation Colt 1851 Navy cap and ball revolver was destroyed! Each gun took weeks to clean, because the residue had gotten into all the cracks and tight places and had to be scraped out with tools.
Several years after that experience, I joined an horology club and attended their meetings for about a year. These are guys who fix watches and clocks, and they had one thing to say about WD-40. Don’t ever use it on a clock! They knew all about the yellow coating it leaves, and several members had horror stories about removing it from clock gears. Apparently, not even ultrasound tanks can remove all of it.
Before you rise up to defend WD-40, know that I use it, too. For certain jobs, it can’t be beat. But not for protecting the finish of a gun. Use Ballistol for that.
What does WD-40 have to do with corn oil? Everything. Like WD-40, corn oil dries and leaves a waxy film on anything it comes in contact with. And that’s why it was originally recommended for spring-piston airguns. Not all spring-piston guns, you understand. Just the ones from China.
Duane Sorenson, who used to work at Compasseco in the 1990s, recommended corn oil for all his Chinese guns because of the waxy buildup. He reasoned that the wax filled in the rough machining marks left inside the cheap Chinese compression chambers, eventually building up to the point that compression increased. He was an active proponent of corn oil in spring guns, and I think many thousands of shooters were told by him to use it.
Duane also said the flashpoint of corn oil was very high, so using it would stop dangerous detonations. As far as I was able to test for that, it did seem to work. But — and this is the point of today’s report — corn oil is not recommended for a sophisticated spring-piston airgun powerplant. The current crop of Tech Force guns do not have compression chambers rough enough to benefit from its use.
Time is the criterion
Duane was advising corn oil for airguns like the B3 underlever and the TS45 sidelever. Those guns really did have rough compression chambers that could benefit from a product that infilled their machining marks. But at the same time he was recommending corn oil, Sorenson was also pushing their Chinese manufacturing partner to better finish the insides of their compression chambers. The result was the Tech Force 36 underlever, which was very smooth inside, and later the Tech Force 99, which was even better.
But while this improvement was happening, Duane was still selling lots of the older and less expensive Chinese spring guns that were still very rough. So, he continued advocating corn oil, even as the many of the guns he sold were getting better and had less need for it.
I tested it
Duane was so insistent on corn oil being a miracle-product that I bought a quart of the stuff and began experimenting with it. That was how I learned that it doesn’t detonate. While I was testing it, I was unaware of why corn oil was being recommended and the fact that many of the more modern chinese airguns didn’t need it.
I conducted several tests using corn oil for The Airgun Letter, but frankly I never got the kind of results Duane told me to expect. Part of that was because I was probably testing it on the wrong guns and part was because I wasn’t using it as much as Duane did. I never saw the long-term effects he told me about.
I expected to see an increase in velocity and a decrease in the total velocity variance. The velocity never increased as much as I had thought, but the shot-to-shot variation did decrease somewhat.
What about corn oil today?
This is the reason I wrote today’s report. Do not use corn oil in any modern spring-piston airgun! Corn oil is meant to solve a level of manufacturing crudeness no longer seen in modern airguns. Like many other things, time has changed the game. We no longer put oatmeal in our car radiators to patch small leaks, and we certainly no longer lubricate spring-piston compression chamber with corn oil.
Just as you don’t want a buildup of hard yellow film on the outside of your airguns from dried WD-40, you also don’t want the waxy buildup from corn oil on the inside. Use the products that are recommended for the job, like a proper grade of silicone chamber oil for the compression chamber of your airguns.
by B.B. Pelletier
Tune is slang for tuneup, and in airguns a tuneup can range from a quick lubrication all the way to a major overhaul of the powerplant and trigger. Everything in between these two extremes is also fair game. So, lesson one is that a tune can be anything that changes and hopefully improves the airgun’s performance.
I’m going to address a breakbarrel spring gun in today’s report. Other powerplants can also be tuned; but the steps are different, and the results will differ from what you get with a spring gun tune. Since the majority of airgun tunes are performed on springers, it’s appropriate to look at them first. And the breakbarrel is the No. 1 type of spring gun.
Victor asked what was meant by a tune, but I suspect that others would like to know what’s involved, as well, so today we’ll look at airgun tuning in all its complexity. Let’s begin with a brand-new spring gun and see why we would tune it and what might be done.
Smoothing the edges
Most new spring guns have sharp edges on all the mating powerplant parts. Sometimes, these edges interfere with the movement of the parts. These edges are worn down during a long break-in period, which is why a gun gains velocity as it wears in. But you can also remove these edges and burrs with small files, and that is one thing that a tuneup can do.
Key places to look are the cocking slot, the piston slot, the cocking linkage and, if there’s an interface between the linkage and the piston, that’s a prime place to look for burrs and sharp edges. The forward edge of the cocking slot is especially important, because it can slice a new piston seal when it’s installed…and that will ruin the seal. The end cap and sides of the trigger mechanism should also be checked.
The action forks that the pivot bolt passes through is another place to look for burrs and sharp edges, as well as the sides of the baseblock that the barrel is pressed into.
There are also burrs and sharp edges that don’t affect the operation of the powerplant. These do not go away with use and they can be left alone if you like. However, if you plan to take the powerplant apart in the future, these edges and burrs will be waiting to cut you.
Probably the most common thing done during a tune is lubrication. New guns can have either too much grease or not enough. And most of them have the wrong kind of grease. The factories use a general machine grease, but there are much better greases that can be used.
For metal-to-metal contact, nothing is better than grease that contains a high concentration of molybdenum disulfide. Moly isn’t a grease — it’s a solid particle that’s ground very fine and mixed with grease for application. When it comes in contact with metal under some pressure, the particles bond with the metal on the surface, forming a layer of extreme low friction. That layer is durable and allows other metal to slide across the surface it’s on.
We don’t appreciate how low-friction moly is, because the grease it’s in raises the coefficient of friction. But custom tuners are known to burnish certain parts of a gun — like the inside of the compression tube — with dry moly particles. This process takes a long time, as the moly doesn’t want to cooperate; but once it’s, done you have a surface with very low friction. Jim Maccari and I split a pound of moly powder, and my half was in several large bottles. It’s a lifetime supply for a full-time tuner!
Another place where moly powder comes into play is on the mating trigger sear surfaces. I’ll have more to say about this in a moment, but this is a custom tuner’s trick. The action fork and baseblock can also benefit from a burnish of moly.
I don’t burnish anymore, though. Moly grease, such as Air Venturi Moly Paste, will do the same thing over time as it gets worked into the action through the process of shooting.
But not every springer needs moly grease. The older guns with leather piston seals actually do better with a white lithium grease. The grease serves as fuel for the constant dieseling of all spring-piston guns, and leather seals burn more fuel than synthetic seals do. For this same reason, I lube the mainsprings of the lower-powered springers like a Diana 27 with the same white lithium grease.
Does it bother you that I said all spring piston guns diesel? Well, they do. Don’t confuse dieseling, which is normal and even good, with detonation — which is when you here a low bang. That’s too large an explosion for your gun, and you don’t want to do very much of it.
The barrel pivot and the forks through which it passes is another place to grease. The right grease (moly) applied here reduces the cocking effort by 10 pounds!
The mainspring is the other place that gets lubed, and often it’s to stop the vibration, though I’m going to tell you in a moment a better way to do. For this, people use black tar, or what Jim Maccari calls Velocity Tar. It’s just a very viscous grease with a high adhesion that feels tacky to the touch. Farmers and heavy equipment operators know it as open gear lubricant. Most of the different greases like this will slow your gun to some extent, but there are products like Velocity Tar which, if used sparingly, seem to not phase the velocity at all.
Remove all the play
Okay, lubricating a gun to smooth the firing cycle is a redneck approach. Many people, including me, do it that way. But there’s a more elegant way if you’re willing to work. That way is to remove all the play in the various moving parts. The piston and mainspring are the primary parts involved.
The piston in a factory gun fits well inside the spring tube, but there’s a looseness to allow for manufacturing tolerances. The piston seal takes up a lot of the slack, but it’s located just at the front of the piston. The rear is free to move in all directions. While the space is small, this is where some of the vibration comes from.
To tighten the piston, it’s possible to put small bearings at the front and rear of the piston. These are usually small, round spots of synthetic material such as Teflon or nylon. Typically, three are placed at the front and three more at the rear. They are spaced evenly around the piston body, and the front ones are offset from those in the rear. If they fit the spring tube exactly, the piston rides on them, and then a moly coating really does its work.
The next critical fit is the mainspring, and here it’s sometimes possible to buy a spring that fits the spring guide in the rear and the piston rod in the front very tightly. Tuners call this close fit being “nailed on.” When you have a close fit like this, good moly lubrication is essential, or the close fit of steel on steel will cause galling, which is a form of burnishing that causes friction, vibration and excess heat.
If you can’t find a spring that fits this tight, you can always have a custom spring guide made that does fit the spring you have. Then, inside the piston, you can put a steel shim that fits between the mainspring and the inner walls of the piston. It’ll look shoddy; but once the powerplant is together, it’ll stay in place. And moly is essential here for the mainspring and the guide. This is called a “beer can” tune, because people often use cans to make the shim.
Another trick people use is to put shims behind the mainspring on the spring guide end. This puts the mainspring under more tension and gives more power. You have to make sure there’s enough room to cock the rifle when doing this, because it’s possible to shim the spring too much.
New airgunners assume that the stronger the mainspring, the more powerful the airgun. That isn’t always the case. Piston stroke has more to do with power than the spring rating. I always look for a weaker spring because I know it won’t subtract that much power from the gun. A coating of tar will do more to slow down a gun than a weak spring, as long as the spring fits well.
A final word on the mainspring is to notice that each end is usually a different size. Try to match the end with the spring guide or piston rod that fits best.
Piston seals used to be a real big reason for tuning a spring gun, because they wore out or melted from friction. Today’s seals are pretty well made, though there will always be some cheapies that come to market from time to time. The thing about the piston seal is to ensure that it fits the bore of the compression tube without adding too much additional friction. Some is unavoidable, but it’s easy to go overboard. The modern parachute piston seal that expands as it compresses air is very sophisticated, and shouldn’t be too difficult to size correctly. To reduce the diameter, put the seal on the piston and rotate the piston against sandpaper. Be careful to keep the sides of the seal parallel to the compression chamber bore while doing this. It usually only takes a minute or two for this job.
The trigger can be adjusted and lubricated during a tuneup. I lubricate with moly grease, because a trigger is not a part that works by friction. No matter how low you get the friction, the trigger should always be safe…but this is a place where home tuners often have problems. They either stone or file the mating sear surfaces and put a dangerous angle on them. Then, they lubricate them with moly. These are the triggers that slip when cocked.
People are also known to adjust a trigger to have too fine mating surfaces, and once more, they’ll slip when cocked. My advice is to lube first, then let the trigger work for several hundred shots before you adjust it. I would keep stones and files away from triggers unless you’re certain that you know what you’re doing.
This part is often overlooked and can sometimes give you a large boost in power. The breech seal doesn’t have to stand proud of the breech to work well. It all depends on how the gun is designed. But don’t overlook the possibility of improving performance by raising the breech seal a few hundredths of an inch.
I hope this report answers most of the questions you have regarding tuning an airgun. As I said at the start, a tune can be any of these things, or all of them. A professional tune is usually all, but you should discuss the specifics with your airgunsmith before letting him start the work.
by B.B. Pelletier
El Gamo 68 is a futuristic breakbarrel from the past.
I’m sure many of you imagine that I’m immersed in airguns all the time, which is true. That my office is filled with all sorts of models (it is) and that my workshop bench is strewn with parts of projects in process. There’s just one problem with that view. I don’t have a workshop. When I really need a lot of room, such as for today’s report, I usually move to the kitchen, where I do my work on that time-honored bench — the kitchen table!
The other thing most readers don’t appreciate is how whipsawed I am with time. I can’t afford to spend a week or even two days on a project anymore. Back in the days of The Airgun Letter, I had one month to crank out the stories that are now written in about four days! If I spend more than three hours on a project before starting to write about it, I’m working on a 12-hour day because the writing and photography take so much more time than the actual testing. And so it was with some trepidation that I approached today’s report, which is a disassembly, evaluation, cleaning and lubrication of my Gamo 68 breakbarrel air rifle.
I wanted to do this because the 68 shoots very suddenly. It doesn’t vibrate like many spring guns, but the thump when it fires is very heavy — way out of proportion with the power of the gun. The trigger is very heavy, and I wanted to see what might be involved in bringing it down. It’s crisp enough, just too heavy for the release.
Because of the potential time element and the fact that I have no room for another disassembled airgun, I studied the rifle carefully for two months — the way a diamond cutter examines an important stone. And with all that study, I still did not recognize the way the gun is assembled. But one look at a schematic sent by David Enoch showed me what to do.
Only three screws have to be removed to take the action out of the stock. That’s no different than any other breakbarrel, but the location of the third screw is certainly different! It’s at the back of the spring tube.
This photo shows the action out of the stock. One extra screw was removed. The one below the triggerguard does not hold the action in the stock. It’s one of two screws that hold the trigger unit to the stock, and it doesn’t have to be removed to get the action out of the stock.
With the action out of the stock, you have access to disassemble the mechanism and do what I ended up doing to the rifle. The trigger is really a complex bullpup unit that’s entirely separate from the barreled action. By “bullpup,” I mean that the trigger blade does not directly contact the sear. It’s located many inches forward of the true sear and is connected by a long lever inside the trigger unit. If I want to improve the trigger-pull beyond what simple adjustment can do, I need to remove this unit from the stock to get access to the pins and levers.
I decided to leave that task for another day, as working on the powerplant was all I had time to do in this session.
You’re looking down into the aluminum stock that holds the spring tube. The trigger unit runs from almost all the way on top, where the trigger blade is located, to all the way on the bottom, where the true sear releases the piston. It’s a complex bullpup unit that must be removed as a unit for work. You can see the steel channel that holds all the trigger parts.
Because of the way the Gamo action is designed, I could set the trigger aside and go to work on the powerplant. The end cap is held in the spring tube by a single large pin that must be drifted out. The action was installed in a mainspring compressor for this next step.
Here you see the barreled action in the mainspring compressor with the large pin drifted out. The pin is on the table, next to the hammer handle. The spring tube is ready to come apart.
Moment of truth
Taking a spring-piston powerplant apart for the first time is always a surprise. You never know how much compression the mainspring is under, even when relaxed, and how far it will come out of the gun before it’s fully relaxed and the gun can be removed from the mainspring compressor. It was a real surprise this time, for the spring came out several inches before fully relaxing. If I had just drifted the pin and tried to hope I could hold the end cap with my body, I could have broken bones!
Like a python that swallowed a telephone pole, the mainspring just kept coming out of the spring tube until it was this far! As you can see, I didn’t have much more room on my adjustment screw.
Once tension is off the mainspring, the rifle can be removed from the compressor. The end cap, spring guide and mainspring can now be removed. The piston, though, is still held in the rifle by the cocking link. You must disconnect the link from the piston before it will slide out of the gun.
The 68 has an articulated cocking link, and I noticed a spot at the front of the cocking slot that was enlarged for the removal of the cocking link. That told me that I did not need to remove the barrel from the action to disconnect the link from the piston. Just line up the link end with the enlarged hole, and the end pops right out.
The cocking link is two pieces.
The end of the link can be removed from the spring tube through the enlarged hole at the end of the cocking slot. The two-piece cocking linkage helps you do this.
The mainspring and piston both told me this gun had probably never been apart before. The grease looked like factory grease, and there were many years of accumulated dirt and grime on all the parts.
The piston has a leather seal that looks brand new. It was a bit on the dry side. After I assembled the rifle, I lubricated it heavily. I’ll continue to do that many times over the next few months, until I’m satisfied that the leather is oily and supple once more.
Leather piston seal looks good.
The piston itself is a very strange duck. It has to be, because the trigger is autonomous from the powerplant. There’s a window on the side of the piston at the rear where the sear catches it when the gun is cocked.
Here you see the entire piston, which is a machined steel part. The rectangular window at the end of the piston skirt is where the sear catches and holds it when the gun is cocked. Only the piston seal and the machined section at the rear touch the inside of the spring tube, so that’s where the moly lubrication goes.
The inside of the spring tube was as dirty as the piston and mainspring. I put paper towels over the end of a long-bladed screwdriver, dipped the paper in alcohol, and cleaned the inside of the spring tube and compression chamber. This would also be the time to remove any burrs from the cocking slot, but there weren’t any on this one.
After the entire powerplant was cleaned, I examined that long mainspring. After all those years, I thought it had to be canted — and it was, though not as much as I’d imagined. Rolling it on a flat surface revealed a wobble at one end, which translated to a jolt during firing. Hopefully, I had a suitable replacement.
I found several possibilities, but the best one proved to be a replacement spring for a TX200, of all things. It’s a special spring Jim Maccari made some years ago and it has collapsed coils in the center and at one end. As you can see in the picture, it’s a lot shorter than the spring that was in the 68. The wire is thicker, but there are so many fewer coils that I knew it would fit. The fit inside the piston was about the same as the factory spring, and the fit on the spring guide was tighter. So, this is a good replacement.
Factory spring above, replacement below. The new spring will certainly be under less compression when the gun is not cocked!
I coated the new spring with a thin layer of black tar and inserted it back into the piston. The front and rear of the piston were then coated with a heavy layer of moly grease and installed back into the spring tube. The cocking link was inserted back into the enlarged hole, where it contacted the piston for cocking.
The spring guide was coated with moly and slid inside the mainspring as far as it would go. The end cap was placed over the end of the spring guide, and the barreled action was installed in the mainspring compressor, once again. This time, the amount the spring stuck out was drastically reduced.
The spring guide is steel. It was coated with moly and slid back inside the mainspring.
The new mainspring has just begun to compress. It’s a lot shorter than the old one!
The gun went together without a hitch! And that was when I noticed for the first time that the entire job from start to finish had taken me only one hour — including photos! That’s as fast as I could tune a TX200 (assuming I would, which would never happen), and it doesn’t require a mainspring compressor. This wasn’t the time-killer I thought it was going to be.
How does it shoot?
The rifle cocked with 22 lbs. of force before this tune. Now it takes 28 lbs. to cock it, and the final sear lockup takes a final crunch that wasn’t there before.
The gun fires with 70 percent less jolting than before, but its just as quick as it was before the tune. The feel of firing is atypical of a lower-powered breakbarrel, just as it used to be. I can now feel a little vibration in the powerplant that I think was previously masked by the heavy firing jolt.
I still don’t know the gun. It will take a session of velocity testing and shooting for accuracy before I can finish this report. Since I’ve already tested the gun extensively before, I’ll combine both of those things in the next report.