Posts Tagged ‘tuneups’
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
Today, I’ll test my Beeman R1 air rifle for velocity, plus show you the differences between the standard Rekord trigger and the special match Rekord trigger. Before I get to the velocity figures, however, let me give you a brief history of some of the many tunes that have been in this gun.
After 1,000 shots were on this rifle, it was shooting Crosman Premiers at an average 770 f.p.s. The rifle took 46 lbs. of effort to cock and shot with a little buzziness, indicating the powerplant had some looseness.
Following that test, the rifle went through a series of tunes that are way too numerous to cover here. One that’s of interest was the Beeman Laserization that was so popular in the 1980s and early ’90s. Beeman would do this tune for a price, or you could buy all the parts and do it yourself. I elected to do the latter.
The Laser seal came way oversized and had to be reduced to fit the particular gun in which it was installed. That was thought to be a superior way of tuning in those days, though today I see generic seals that work just as well without all the fuss.
I had a problem fitting the first seal, and it burned on one edge from excessive friction. I got a replacement and sized it a bit looser. You never want to lube a Lazerized rifle, as the special Beeman Laser Lube is the best stuff for friction. This lube is no longer sold. If you have a worn-out Laser seal, just about any modern generic seal can replace it with no loss of energy.
The Laser spring was weaker than the factory spring, making the rifle easier to cock. After I applied the tune and broke it in a little, my rifle averaged 765 f.p.s. with Crosman Premiers. Cocking effort was 37 lbs., which is an 11-lb. reduction for almost the same power. That’s significant!
The one thing I didn’t like about Laserization was the fact that the gun vibrated a lot more than before. That Laser spring fit the piston and guide so loosely that the only way to quiet the gun was to use Mainspring Dampening Compound on the mainspring — which subtracted velocity at the same time.
The absolute best tune I ever applied to the R1 was a Mag80 Laza Tune I got from from Ivan Hancock. It was a drop-in tune that included a buttoned piston and a long mainspring that came coated with something I called black tar in print the first time I wrote about it. After that, the airgun community seized on the term, and black tar became a product — though nothing that was ever sold separately was as viscous as the stuff on that Venom spring.
This tune took the R1 up over 22 foot-pounds with absolute zero vibration. It was so smooth I thought it had actually lost power. But the 50-pound cocking effort reminded me that the big spring was doing its thing. For reference, Crosman Premiers averaged 809 f.p.s. with this tune.
Unfortunately that spring was included in my Mainspring Failure Test, that left four different tunes cocked for one month to see the effects. The spring finally canted and was never as smooth afterward!
I also tested a gas spring made by Vortek. It was smooth and did make better than 20 foot-pounds with certain pellets, but it also took 50 pounds of effort to cock, so I have since removed it from the rifle. The gas spring put Premier pellets out the muzzle at around 790-795 f.p.s.
The tune that’s in the rifle now is a weak mainspring and a generic piston seal. Everything is moly-ed and I have used a touch of Black Tar on the mainspring to calm it down. Today we will all see what velocity the rifle currently develops with this tune, which can be researched in its entirety in the 13-part report titled Spring Gun Tune.
The first pellet I tested was that old standard — the Crosman Premier. I have given you the velocities for this pellet at various stages of the rifle’s life, so you can compare them to how it’s doing now. With the current tune the rifle shoots Premiers an average 743 f.p.s. The range runs from a low of 738 f.p.s. to a high of 751 f.p.s., so an extreme spread of 13 f.p.s. Given the pellet’s average 14.3-grain weight, the rifle produces 17.53 foot-pounds at the muzzle with Premiers. I noticed they fit the breech on the loose side, but were still what I would consider a good fit.
The rifle now cocks with just 33 pounds of effort, which is where I like it. It weighs 11 pounds on the nose, and you have to allow a little over one of those pounds for that big Bushnell Trophy 6-16 scope and mounts.
Next I tried RWS Superdomes, another domed pellet like the Premier but made of pure lead and just slightly heavier, at 14.5 grains. These averaged 742 f.p.s. in the test rifle and ranged from a low of 733 to a high of 748 f.p.s. So a 15 foot-second spread. At the average velocity this pellet produces 17.73 foot-pounds of energy at the muzzle. The fit was loose in the breech.
Then I tried the heavier 15.43-grain Gamo Hunter. This dome fit the breech loose but also varied a lot in the seating pressure required, which indicates variability in the size. They averaged 706 f.p.s. and ranged from 700 to 710 f.p.s., which is a tight spread of just 10 f.p.s. At the average velocity these pellets produced 17.08 foot-pounds of energy.
The final pellet I tested was the 15.9-grain JSB Exact dome. These averaged 696 f.p.s. and ranged from 693 to 701 f.p.s., so the spread was just 8 f.p.s. — the tightest of the test. The fit of this pellet was loose in the breech. At the average velocity this pellet produced 17.11 foot-pounds of energy at the muzzle.
I mentioned that the trigger in the R1 is a standard Rekord, and when I reported on the HW55 target rifles, I had mentioned that they all have special match Rekord triggers. Weihraiuch now calls all of their Rekord triggers match triggers, but back when the 55 was still being offered they differentiated between the trigger in that gun, which they called a match trigger and the one they used in every other sporting rifle. The latter was just called a Rekord.
This is the standard Rekord trigger that’s on my R1. Paul Watts gave me the smooth trigger blade to replace the Weihrauch grooved blade that comes on the trigger, but otherwise the trigger unit is stock. I have adjusted and lubricated it, of course.
The match trigger also has no provisions for a safety, in contrast to the standard Rekord. Target guns are seldom provided with safeties, as their shooters are expected to be cognizant of safe shooting at all times.
The match Rekord has an aluminum collar around the trigger adjustment screw that is used to lock the screw after adjustment. This collar is turned by hand-pressure, only, so it is knurled on the outside to provide a better grip. Let’s sample the R1 trigger against an HW55-CM trigger and see how they differ in use.
The R1 trigger breaks cleanly at 1 pound 1 ounce — a little lighter than the recommended 1 pound 8 ounces that the Beeman instructions used to recommend. You have to remember that I have shot this rifle extensively since it was new and I have worked on the trigger, as well.
The match Rekord in my HW55 CM breaks at 7 ounces, or just less than half of where the standard Rekord goes off. It is considered very safe at this low pressure setting, because of both the design of the Rekord and that fact that a target shooter will be handling the rifle.
The two Rekord triggers are dimensionally the same. The proof of that is my HW55 SF that is an HW50 with this trigger instead of the normal Rekord that’s found on the HW50s. Back when the 55SF was made, the HW 50 was a different model than today, but the same gun could accept either trigger.
Should you swap your trigger?
The question that always comes up when I tell people about these two triggers is why not just adjust a standard Rekord to have a pull weight equal to the match trigger? The answer is the match trigger isn’t designed to hold back pistons that are compressing powerful mainsprings like those found in an R1 — or even in lesser sporting rifles. And, if you were to install a match trigger in a sporting rifle, you would be doing the same thing. So leave the trigger that came with the gun where it is and be safe.
That’s it for today. Next we will look at the accuracy potential of this rifle.