Posts Tagged ‘tune up’
What is a tune?
by B.B. Pelletier
Announcement: Bill Cardill is this week’s winner of Pyramyd Air’s Big Shot of the Week on their airgun facebook page. He’ll receive a $50 Pyramyd Air gift card. Congratulations!
Bill Cardill submitted this week’s winning photo for BSOTW.
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.
Lubrication
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
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.
Trigger
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.
Breech seals
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.
The HW 55CM target rifle: Part 4
by B.B. Pelletier
Is this Custom Match the best HW 55 ever made? Read the report to find out.
In the last report, I tuned the rifle and got rid of the objectionable firing cycle. It’s always a great pleasure to return to a classic air rifle like this one after testing so many modern airguns, because these oldies are so reserved and well-behaved. I know it’s not going to kick, roar and fight me at every turn. It may only be suited to shoot 10-meter target, but sometimes — and by that I really mean often — that’s exactly what I need.
Sight-in
I had to remove the sights during the tuneup, so the rifle needed to be sighted-in again. It wasn’t that far off, but the indices are so dark on a 55 rear sight and my eyes are so bad that I had to play around until I discovered which way to adjust the sight to go right. In this respect, a modern 10-meter rifle has it all over a vintage one.
The first pellet I tried was the H&N Finale Match Rifle pellet. I haven’t had a lot of recent success with this pellet in target rifles, but in the past this was one of two to contend with — the RWS R-10 Match Pistol pellet being the other. This time was different, though. Although the first group wasn’t what I wanted, it showed enough promise that I shot a second and a third. By the third group, I could tell this pellet likes this rifle.
Not bad! Five H&N Finale Match Rifle pellets went into this group at 10 meters. Any one of them could be a 10 if the sights were adjusted.
Next, I tried the RWS R-10 Match Pistol pellet, and I gave it the same number of chances, but it never showed me anything. That was a surprise, because I think this pellet is one of the more accurate pellets in several of my other 10-meter rifles.
Five RWS R-10 Match Pistol pellets made this nice round group. This is impressive to anyone but a veteran target shooter, who would see that it’s about twice the size it needs to be.
Following the R-10, I tried the RWS Hobby pellet, because in my HW 55 SF — the 55 that has no barrel lock — Hobbys do surprisingly well. Again, there was no joy this time. I’m showing the group to contrast with the others in this report.
RWS Hobby pellets are just not right for the HW 55CM.
At this point, I was satisfied that this rifle is accurate, though it won’t give an FWB 300S any competition. But why stop there?
I next mistakenly loaded some obsolete and nondescript European diabolos that I mistook for JSB S-100 competition pellets. Boy! If you ever wanted to see a comparison between good pellets and cheap ones in a good gun, this was it! How about a three-quarter-inch five-shot group?
Back to serious ammo. The next pellet I tried was the H&N Match Pistol. This is not a Finale Match pellet, and I find that these sometimes vary in weight a lot more than Finales tend to, but there can be surprises. Not this time, though. The best group looked like Hobbys. Oh, well!
After that, I tried H&N Match Rifle pellets. They’re the same as Match Pistol, only heavier. But for some reason that nobody understands but everybody believes, they shot great! These are the pellets for this rifle — until I find something better.
Now, this is what we’re after! Five H&N Match Rifle pellets are obviously working very well in this rifle. This would be the pellet to stick to until a better one comes along.
Overall evaluation
The rifle is shooting fine with the new tune. I could live with less power, but what I have isn’t bad. The trigger is a joy, because it breaks at just 7 oz., and that’s as light as I need it to be. Shooting from a bench in the rested position doesn’t give you the full feeling of the rifle. All it shows is the potential for accuracy, and this one’s got it.
The HW 55CM target rifle: Part 3
by B.B. Pelletier
Is this Custom Match the best HW 55 ever made? Read the report to find out.
This is a special Part 3 for the HW 55 Custom Match target rifle. It will be a retest of velocity, following a strip-down and lubrication with black tar to get rid of some uncomfortable vibration when the gun fires. When I tested it for velocity in Part 2, I discovered the rifle was shooting way too fast for an HW 55. Probably the Beeman Company replaced the mainspring when it went back to them for an overhaul. At any rate, when RWS Hobby pellets average 694 f.p.s., as they did for this rifle, you know something is wrong. I’ll try to remove as much of the harshness as I can with this tune, and I really don’t care how much velocity is lost.
A word about the Part 2 report is needed here. I combined it with Part 2 of the report on Mac’s Diana model 60 target rifle because I don’t want to crowd the blog with too many reports about vintage air rifles. Since the velocity report goes pretty quick, I just put the two of them together. But, today, the 55 CM gets its own report, because as well as testing velocity I’ll be disassembling the rifle and applying a tune. There will be some observations for that, as well as the velocity results afterward, so this work rates a report of its own. Of course, there will still be a Part 4 accuracy test to come.
Disassembly
There were no real surprises when disassembling the rifle, except to find a very canted mainspring. That was where the vibration came from — of that there can be no doubt. I rooted around in my collection of replacement mainsprings and found one that Jim Maccari made for a TX 200! Talk about inappropriate for an HW 55 — but the dimensions of this spring were so great that I had to try it.
I discovered that the trigger was still coated with a drying, tacky layer of factory “tractor grease.” I kidded Hans Weichrauch, Jr., about this years ago and he had no comeback. From his perspective, the grease is always fresh and new. I removed everything I could from the trigger but expected no change in performance. This was more of a conservation step than a restorative one.
The new spring was very liberally buttered with black tar, and the rifle was assembled once more. However, when I cocked it the first time, I knew that wasn’t the solution. The cocking effort started out light but quickly stacked until I was pulling back around 30 lbs. of effort. That’s way too much for a 55 target rifle.
On the plus side, I probably added at least another 50-75 f.p.s. to the velocity. But, with a target rifle, who needs velocity?
So, once more, the action came apart. This time I used a spring that had very similar dimensions to the one that came from the gun — only this one is straight. It got buttered with tar, too and then everything went back together.
How does the rifle feel?
The rifle now requires 26 lbs. of force to cock, compared to the 20 lbs. before — so that part isn’t good. The firing cycle, however, feels lighter and much quicker. Gone is the objectionable vibration that came from the canted mainspring. This rifle will now be easier to shoot accurately.
Velocity
The first pellet tested was the RWS Hobby that was such a speed demon with the old tune. Back then, the rifle averaged a blistering 694 f.p.s. with this pellet. That’s way too fast and does nothing for the potential accuracy. The extreme spread was 17 foot-seconds with that pellet and tune.
With the new tune, Hobbys average 603 f.p.s., ranging from 602 to 610 f.p.s. for an 8 foot-second spread. That’s more like what I wanted, and maybe even on the low side of what I was looking for. But with that tight spread, I know the rifle is doing well with this tune.
Next, I tried H&N Finale Match Pistol pellets. The old tune gave an average 632 f.p.s. velocity with a 14 foot-second spread.
The new tune gives an average of 573 f.p.s. with a 12 foot-second spread that runs from 567 to 579 f.p.s. The spread is pretty close to what we had before, but the velocity is now down where I expect it to be.
The last pellet I tested was the RWS R-10 Match Pistol pellet. With the old tune, the pellet averaged 632 f.p.s. with an 18 foot-second spread that went from 619 to 637 f.p.s.
The new tune sends this pellet downrange at an average 565 f.p.s. with the total velocity spread that runs from 560 to 567. Only 7 f.p.s. separates the slowest shot from the fastest.
Firing behavior
The rifle now seems much more calm and settled when it fires. I can’t be sure until I shoot for the record, but I think I’ve tamed the beast.
Am I satisfied with this tune? Yes, except for the extra cocking effort. An HW 55 should cock at around 15 lbs. of force, and this one takes 26 lbs. That’s heavy, even though it doesn’t set off any alarms. I would still like to get it back under 20 lbs., but I’m not going to hold up the show just for that.
Accuracy testing is next, and then we’ll have complete tests for five popular 10-meter spring-piston target rifles: the HW 55 SF, FWB 150, Diana model 60, Walther LGV Olympia and this HW 55 CM. Guns I haven’t yet tested (that I own and have access to) are the FWB 300S and the Haenel 311.
A shrine built for a Feinwerkbau 124 – Part 14
by B.B. Pelletier
Part 13
Part 12
Part 11
Part 10
Part 9
Part 8
Part 7
Part 6
Part 5
Part 4
Part 3
Part 2
Part 1
Airgun Academy videos #19 and #20 are now available.
2011 airgun show calendar
Before I get to the report, here’s a calendar of all the 2011 airgun shows I know of. If you want to go to an airgun show, here they are.
March 5 & 6
Pacific Airgun Expo
Placer County Fairgrounds
Roseville, CA
Contact Jon Brooks @ 707-498-8714
pae@pacificairgunexpo.com
April 9
Flag City Toys That Shoot
Lighthouse Banquet Facility
10055 S.R. 224 West
Findlay, OH 45840
Contacts:
Duane Shaferly @ 419-435-7909
Dave Barchent @ 419-423-0070
Dan Lerma @ 419-422-9121
To register contact:
FlagCityToysThatShoot.com
April 15 & 16
2nd Arkansas Airgun Extravaganza
Fairgrounds, Exit 98A on I-30
1605 Martin Luther King Blvd.
Malvern, AR 72104
Contact Seth Rowland
June 11 & 12
5th CT Airguns Airgun Show
Windsor Elk Lodge
Windsor, CT
Contact Kevin Hull @ 860-649-7599
July 15 & 16
Airgun Show and Shoot
American Legion Post 113
Baldwinsville, NY
Contact Larry Behling @ 315-695-7133
August 21
Daisy Get Together
Kalamazoo County Fairgrounds Expo Center
Kalamazoo, MI
Contacts:
Wes Powers @ 517-423-4148
Bill Duimstra @ 616-738-2425
September 17
St. Louis Airgun Show
Stratford Inn Garden Room
800 S. Hwy. Dr.
Fenton, MO 63026
Contact Gary Anthony @ 636-861-1103
This is the 14th report I have made on the FWB 124. In all that time, I was mostly tracking a single 124 — the one I obtained that had been packed for eternity in a wooden case like an Egyptian sarcophagus. We went through many tunes with that gun and saw what each one did. Then, I tuned a 124 for Mark Taylor, a shooter I met at Roanoke. That one wasn’t planned, but it did give us a look at a later and different rifle.
Today, I’m reporting on the bluebird buy I happened upon while registering a firearm several weeks ago. The guy at the gun store owned this 124 that had suddenly stopped shooting, a fault that is common with this model because of a bad formula of synthetic used in the piston seal. You’ll also see it in FWB 150 and 300 rifles, Walther LGV air rifles and probably a lot of other airguns made back in the 1970s. The fix is to install a new seal. You’ve already seen me do this several times in this series, but the one thing I haven’t shown you is what the old seal looks like when it’s broken up inside the gun, and that’s something all airgunners should know.
I originally thought I was going to tune this for the guy at the store, but he wound up selling me the rifle, so I’ll do both a velocity test after the tune and an accuracy test using the curious little Bushnell scope that came on it.
How the new gun differs from the old
Before I tear into the action, let me report on how this later 124 differs from the ones I have already shown you. The Deluxe models weren’t made when this one was built. It’s called a Sport, but it has a checkered grip and sling swivels, two features from the older Deluxe class. Gone, however, is the Wundhammer palm swell, and the cheekpiece that’s on the left of the butt of this later rifle is so small and ill-formed as to make the rifle nearly ambidextrous. With the ambi-style safety and the ease of breakbarrel loading, it should have been an ambi from the start.
Disassembly
When I tore into the gun, I initially wondered if it had ever been apart. The serial number is 42,648, which places the gun very late in the production cycle. So, it could have been a virgin rifle, but it wasn’t. The mainspring was coated with moly grease, a sure sign that someone has been inside, because the factory used only clear grease. From the look of the tune — moly on the mainspring, an FWB mainspring instead of an aftermarket spring, a replacement FWB piston seal (a Beeman trademark, even though they knew about the disintegration problem) and the trigger adjusted very nice — I believe this rifle was last tuned by Beeman. All those characteristics are the ones Beeman would do. As good as they were, even Beeman could not prevent that piston seal from decomposing. And, that’s what I want to show you.
This is what a decomposing FWB seal looks like. The brown particles you see used to be hard, tough synthetic. Now, they’re soft, waxy particles that break apart easily.
In this view, you see hundreds of smaller particles in the tube; and at the bottom (the end farthest from you in this picture), the top of the piston seal has broken off and wedged itself against the end of the compression chamber. The small hole at the lower right inside the compression chamber is the air transfer port. All of this mess must be removed before the rifle can be tuned.
There isn’t much left of the piston seal after it disintegrates. Most has been left inside the compression chamber, but this root has to be cut out of the piston top. Like most of them, this one popped out easily.
I won’t say anymore about disassembly and reassembly except for one thing. Installing the bolt that holds the trigger assembly in the gun is a tricky job. The trigger assembly has the spring guide and is what keeps the whole powerplant together. The bolt is hardened steel, but the trigger housing into which it threads is softer aluminum. You can easily cross-thread the bolt if you aren’t careful. If you do, the trick is to remove the trigger housing from the gun and carefully thread the bolt into the hole, keeping the head aligned straight. It’ll reset the threads in most cases and you’re home free. You can then assemble the gun, and the bolt will not cross-thread anymore. This is the biggest reason you need a mainspring compressor to do this job.
This large bolt with the two flats for gripping is what holds the 124’s powerplant together. It threads into the soft aluminum trigger housing and can easily be cross-threaded. This photo shows an older 124 trigger assembly, not the one from the newer gun I’m testing in this report…which has an aluminum trigger blade.
Many tunes — final satisfaction
I tried several combinations of springs and piston seals until I settled on the Maccari Mongoose spring and seal. At first, the seal was way too tight, as it’s supposed to be, so I sized it by hand-sanding until it had just a little resistance in the compression tube. The spring was lightly lubed with moly grease, and the seal also got a coat of moly before going back into the gun.
Crosman Premier 7.9 lites
The first pellet I tried with the new tune was the Crosman Premier 7.9-grain “lites.” They’ll be among the most accurate in this rifle; history has proven many times. They averaged 761 f.p.s., with a spread from 752 to 770 f.p.s. The average velocity produced a muzzle energy of 10.13 foot-pounds. All pellets were tight in the breech
RWS Hobbys
Next, I tried RWS Hobbys, a 7-grain pellet that’s the speed-demon of the lead pellet world. They averaged 821 f.p.s., but a curious thing was happening as I shot them. The velocity kept increasing! Shot one went just 767 f.p.s., but the fastest shot among the 10 I fired went 832 f.p.s. With the average working out to 821, you can see that velocity was climbing all the time. I think this tune will wear in to the point that the Premiers will go about 800 f.p.s., and the Hobbys will get up to 860 or so. At the average velocity, the muzzle energy was 10.48 foot-pounds.
Beeman Silver Jets
The last pellet I tested was the vintage Beeman Silver Jets that are no longer available. They were the No. 1 go-to pellet when the 124 was in its heyday. Back in Part 10 of this report, I tested them against the best of today’s pellets, with the result that they weren’t far from the leaders.
The 8-grain Silver Jets averaged 732 f.p.s., with a range from 721 to 747 f.p.s. At the average velocity, they were generating 9.52 foot-pounds.
Trigger
I mentioned that this rifle has a nice trigger. It’s sort of a single-stage, by which I mean that pressure is there immediately when you begin the pull, and there’s no obvious hesitation. It breaks with only 26 oz. of pressure, and it feels like less than a pound. I have to be very careful, because I’m used to three-to-five-pound triggers on the rifles I shoot the most. This one feels like nothing to me.
Most 124 triggers have more creep in them than this one. When I owned Mrs. Beeman’s personal custom 124, the Queen Bee rifle, I found that the Beeman company could really adjust a 124 trigger very finely. Whenever I feel a good one, I always suspect someone from Beeman has been inside.
Well, that’s it for this test. Next time, I’ll see about sighting-in the rifle with that unusual scope.
A shrine built for a Feinwerkbau 124 – Part 13
by B.B. Pelletier
Part 12
Part 11
Part 10
Part 9
Part 8
Part 7
Part 6
Part 5
Part 4
Part 3
Part 2
Part 1
The November podcast has been posted.
Before we begin, my buddy, Randy Mitchell, who was also the outlaw, Dakota, from Frontier Village (an amusement park in San Jose, California, from 1961-1980) sent me a photo from over 40 years ago. I was Casey Jones, the engineer who ran the railroad at the Village, and Dakota had put an obstruction across the tracks out in the badlands. When I stopped the train, he jumped me at gunpoint and forced me to clear the rails. Then, he stole my boots and drove the train back to the station himself. How time flies!
Dakota forced me to clear the obstruction, then stole my boots and drove the train back to the station himself. I had to walk back!
Now, on to today’s report. Well, well. How the tide turns when you go to an airgun show! I went to Roanoke hoping to score an FWB 124 to tune and instead I picked up one to tune for somebody else. That’s usually a good thing, because when I tune for other folks I do a better job. I’m like the cobbler whose children are barefoot.
You’ll remember from Friday that this rifle is Mark Taylor’s, and I gave you an idea of how it performed. The cocking was too hard, plus there was a scraping or grinding feel to it. Well, once I got the guts out I found out what that was and why it happened. But, I’m getting ahead of myself.
The first comment I’ll make is that Mark’s rifle hasn’t been apart many times. The mainspring I removed looked like a 124 mainspring, except that it had 39 coils — and a standard spring I have has only 35. So, the spring I removed was much longer than standard. At least I think it’s longer. Heck, it’s been so many years since I tuned a 124 that I doubt I know anything for sure anymore.
Looking through the cocking slot before disassembly, you can see that the mainspring has been coated with moly grease.
The second comment is that Mark’s rifle had the strangest lubrication I’ve ever seen in any spring rifle, and I include my older San Anselmo rifle in that observation. My gun was tuned back in the day when it was standard practice to use an entire jar of Beeman’s moly grease on the mainspring of a 124. When I took that gun apart the first time, I was scraping grease from everywhere! Had I known how full it was, I could have called Mike Rowe and gotten him to put it on his Dirty Jobs TV show.
In contrast, Mark’s rifle was almost dry inside! Only the mainspring was coated with moly, and it looked like a smear of lithium grease might have been applied to one spot on the back of the piston. As a result, the piston was touching the top of the spring tube when the gun was cocked and had galled (made shiny by removing a small amount of metal) a large area that wasn’t too deep. It wasn’t serious, but it also was never going to get any better.
This is how the piston looked immediately after removing it from the gun. There’s no lube on the seal!
This is the back end of the piston, called the skirt. As you can see, it has next to no lubrication.
The scraping, grinding feel came from this area. Those two bright lines are galled metal, where the piston skirt scraped against the inside of the spring tube. The damage is minor and correctible with the proper lubrication.
I discovered this lack of lube when I cleaned the inside of the spring tube. It was practically dry and grease-free in there. If I had tuned it, there would have been a lot of moly burnished into the metal and the cleaning patches would have come out black instead of white.
Using moly grease on the mainspring isn’t the best thing when you want a smooth shot cycle. That’s where Maccari’s Black Tar comes into play. A dry piston isn’t the right thing for this gun, as evidenced by the galled metal. I lubed the front and rear of the heavy 124 piston with moly grease. Gene Salvino, Pyramyd Air’s tech manager, recommends using lithium grease on their piston seal, but I used moly on this one because of the galled metal.
The piston seal that was in the rifle looked to be in fine shape. Since this was supposed to be a test of the new Pyramyd Air seal, I removed it anyway. I’ve never seen another one like it and have no idea where it came from.
I also noted that the baseblock bearings weren’t lubricated with much of anything, which might have added to the cocking effort. Also, the barrel pivot pin was dry. I spread moly grease on both the bearings and the pivot bolt before installing them in the rifle again.
I selected an old Maccari Deluxe tune kit for the rifle. This kit drops in, but is made so perfectly that the mainspring goes on the spring guide like it was nailed on. That’s tuner’s slang for a very tight fit. The spring diameter expands when it’s compressed lengthwise, so the fit isn’t as tight as it seems when you install it. There was also a Delrin spacer for the spring guide that put a little more tension on the spring.
This is how to lubricate a 124 piston correctly. Both the front and rear of the piston can contact the other metal surfaces inside the gun. The center of the piston is smaller and cannot touch anything. Besides this, I also burnished moly inside the spring tube before installing the piston.
All metal-to-metal contact surfaces except for the outside of the mainspring got a coat of moly grease before the gun was assembled. The outside of the mainspring was buttered with Black Tar. Then, the gun was assembled in reverse order from disassembly.
This is how I “buttered” the mainspring with Maccari’s Black Tar mainspring dampening compound.
On to shooting
The proof is in the shooting, and the first time I cocked the assembled rifle it worked as it should, which doesn’t always happen. I noted that the cocking effort didn’t seem to have decreased much, but the cocking cycle was now as smooth as it should be. Then, I shot the rifle.
Wow! What a beautiful tune this is. Not only is all vibration gone, but the forward recoil I had noticed disappeared, as well. The gun just sort of pulses when it’s shot.
I then measured the cocking effort and was stunned to find it had increased a pound to 28 lbs. of effort. Personally, I think it’s too heavy for a 124, but the smooth shot cycle is too nice to ignore. Let’s see what is does over the chronograph.
Crosman Premier lites
The 7.9-grain Crosman Premiers averaged 744 f.p.s. with this tune. The spread ranged from 736 to 750 f.p.s. That’s a little tighter than the original tune, and much smoother. The average muzzle energy was 9.71 foot-pounds.
RWS Hobbys
RWS Hobby pellets averaged 784 f.p.s. The spread went from 776 to 793 f.p.s. Again, a slightly tighter spread than before. The average muzzle energy was 9.56 foot-pounds, and a super-smooth shot cycle.
JSB Exact 8.4 grains
JSB 8.4-grain Exact domed pellets averaged 723 f.p.s., a surprisingly low figure. They ranged from 713 to 730 f.p.s. and produced an average muzzle energy of 9.75 foot-pounds. They shot just as smooth as the other two pellets.
What to do next?
This is a toughie. The rifle is cocking and shooting extremely smooth right now, but the cocking effort is a bit high. Mark, the owner, says he doesn’t mind that, as long as the gun shoots smooth, which it definitely does. I’m at the point of a decision that I’m going to let Mark make. I feel certain that the Black Tar on the mainspring is what’s slowing down the gun just a bit. As tight as the mainspring fits, it probably isn’t necessary. Still, the gun does shoot very smoothly, and almost all of the forward recoil seems to be gone, as well. From a shooting standpoint, this is a fine tune. I’ll let Mark decide.
If he wants more power for the cocking effort, I would remove the Black Tar and lube the mainspring with moly grease. But, if he wants a super smooth shot cycle, we have that right now.
Mark, what would you like me to do?
A shrine built for a Feinwerkbau 124 – Part 6
by B.B. Pelletier
Tuning by Earl “Mac” McDonald
Part 1
Part 2
Part 3
Part 4
Part 5
The saga of tuning the FWB 124 continues. While he was here, Mac replaced the Mongoose tune in my 124 with a fresh Maccari Old School kit, which consists of a Blizzard piston seal, a short mainspring and a spacer that slides inside the piston ahead of the mainspring. This he cheerfully did.
You may recall that my 124 was giving an average of 800 f.p.s. with the Mongoose kit. I felt that was too slow and wanted just a little more — perhaps 840 with Crosman Premier lites. The words on Maccari’s website seemed to indicate that the Old School tune was the ultimate way to go, so I ordered one.
The kit arrived, and I was going to install it when the hospital adventure began. So, when Mac arrived, he had the time and I asked him to do it for me. He certainly knows how.
He had to use my mainspring compressor to get the rifle apart but was able to put it together with the Old School kit without using the compressor. No Black Tar dampening compound was used with this tune because the Old School kit is supposed to fit so well it doesn’t need it. Mac put some moly grease on the outside of the mainspring and buttoned up the rifle.
In the hospital, I waited with great anticipation for the results, which came the next day. According to Mac, the new tune averaged around 740 f.p.s. with Premier lites. Seven forty! I was devastated! Well, maybe Mac was reading the chronograph wrong. I vowed when I got home that I would check it.
I asked Mac to remove the hump on the piston seal, thinking it might be the cause of the lower compression. He used a Dremel tool rasp to cut the crown smooth, as I requested, but no change in velocity. So much for my theory of the wasted compression space caused by the high crown.
My check
I shot Premier lites and got the following velocities:
770
763
762
764
764
The shots were accompanied by a burning oil smell, so the powerplant may be over-lubricated at some point. I will disassemble it to determine what to do next. On some guns, I might suspect the compression chamber.
I’ve examined the 124’s compression chamber and know that it is in good condition, but allow me to show you one that is not. Remember the Slavia 622 rifles I tested for you a while back? If not, read this.
What to do?
My next step will be a teardown to check what’s going on inside this gun. I may be able to refresh the tune and get it up to snuff from there. If not, I may install another type of piston seal left over from 124 testing years ago. The journey continues….
A shrine built for a Feinwerkbau 124 – Part 5
by B.B Pelletier
Before I start, a couple of reminders. First is the Facebook event on Tuesday, April 8, at 8 p.m. Eastern. I’ll be on the Pyramyd Air Facebook page for an hour to answer questions you send in. To ask questions, you need a Facebook account and you must be a Friend of Pyramyd Air. Register early and don’t miss out.
Next, don’t forget the Arkansas Airgun Extravaganza, April 30 & May 1. This airgun show is open to the public on Friday, 10 a.m. to 6 p.m., and Saturday, 9 a.m. to 4 p.m. Six-foot tables are $50 each. Admission is $5. Kids 12 and under get in free with an adult. Dealer setup is on Friday, 8 a.m. to 10 a.m. Visit the show website here.
The show is filling fast, and it looks like it’ll be larger than last year’s Little Rock show, which it replaces. I hope you consider attending. I’d sure like to meet as many of you as possible, and I’ll be bringing several of my airguns to show and possibly to shoot, including today’s rifle.
Also, a word to show-goers. If you’re going to attend the show only on Saturday, come before noon. Airgun dealers get antsy toward the end of every show and start packing up early. Unlike gun shows, they’re not penalized for this. Get there while the show is still running strong.
Today, I’ll tell you what I did to the 124 after discovering that the Mongoose kit wasn’t performing up to my expectations. You may recall that it was shooting Crosman 7.9-grain Premiers at an average of 670 f.p.s. I had expected at least 840 f.p.s. Although the firing behavior was very smooth and delightful, I had hoped to break at least 800 f.p.s., so I continued to work on the rifle.
First, I removed the mainspring only and wiped off about 3/4 of the black tar grease. That still left enough to kill all vibration, and the velocity rose to about 700 f.p.s. That’s a gain of about 40 f.p.s. It’s possible to remove the mainspring without a total disassembly, so it was quick and I did it first to see what gains there would be.
Next, I completely disassembled the rifle and removed all the lubrication from the powerplant. I carefully relubricated it very sparingly, keeping the use of tar confined to the outer coils of the mainspring. That got me to 710-720 f.p.s., which was about as far as the Mongoose kit is going to take me.
I’d treated the Mongoose kit as a drop-in instant power booster, and apparently it’s not. It’s more of a 1970s-era 124 kit that needs to be coaxed to shoot as fast as possible–just like the factory 124. I discovered something very important about the piston seal. It’s domed. With that shape, it’ll never produce the absolute fastest velocity since the top of the dome stops it from compressing all the air in the chamber. It may seem like a small thing when you look at it, but this last bit of compressed air is where the big things happen. Maccari has made this seal to cushion the piston blow rather than develop maximum power, so consider that when you order your tuneup kit.
The Mongoose piston seal has a raised, dome-shaped crown. It cannot compress all the air in front of it.
Compare this Surrey 124 seal to the Mongoose seal. See how flat it is on top?
At this point, there were several different directions open to me. One was to start shimming the Mongoose mainspring for extra compression. That would boost power. Another was to abandon the Mongoose seal in favor of a flat one. That would compress the air more thoroughly and give more power.
I took a third step that’s not available to any of you. From my years of working on argues, I had other mainsprings available. I selected a stouter one that was shorter but had a spacer top hat on one end. The other end fit the spring guide very tightly because this was an experimental Maccari 124 mainspring. I retained the Mongoose seal for smoothness and assembled the rifle with minimal lubrication. No black tar because the new spring fit much tighter than the Mongoose spring. I used moly grease on everything. I knew I would lose some power with the Mongoose seal, but that was okay for now. All I wanted was a working 124 with decent power.
As I assembled the rifle, I also answered someone’s concern about the safety spring. They had heard it is a concern when assembling a 124, but I say as long as your spring compressor is a good one the safety spring is easy to install. Hopefully, the pictures will show you how it’s done.
This is the 124 trigger unit with the safety slide and spring removed.
Here’s the spring I’ve been calling the safety spring. It’s actually a trigger-return spring, but it presses against the safety slide.
And here’s the safety slide on top of the trigger unit. You can see the spring between the trigger unit and this slide. As the trigger unit enters the spring tube, the safety slide is pressed flat and retained. There’s really no difficulty installing these parts as long as you use a mainspring compressor.
Following this tune, the rifle is averaging 800 f.p.s. with 7.9-grain Crosman Premiers. While that’s not as much as I want, I’m fine with it for the moment. The gun fires quick and doesn’t vibrate when it shoots, so the tighter parts are as trouble-free as can be. The velocity varies between 783 f.p.s. and 802 f.p.s. Experience tells me this will tighten, and the average velocity will increase by 10-15 f.p.s. as this tune wears in.
I’d planned to test the rifle for accuracy at this point, but I’m not yet finished with the project. The barrel’s gunked up with oil and grease that I don’t want to clean out until I’m done tuning.
My plan is to now install a Maccari Old School kit and be done with it. This is the kit I used to install in 124 rifles 15 years ago, and I know I can expect a velocity over 840 f.p.s. with 7.9 Premiers. The best result I ever got is still averaging 880 f.p.s.
Well, this little adventure has turned into quite the saga, hasn’t it? I never envisioned spending this much time with this rifle. Now that I have, I’ve decided what to do with the gun in the future. I’ll keep the rifle outside the case and shoot it from time to time. It was silly keeping it tucked away where I got to see it only every couple years. That isn’t what this rifle was made for, and I intend getting the full value out of it.
Someone asked me what all this tuning does to the value of the gun. Well, the box only adds value in a non-monetary way. Yes, it’s worth more than a rifle by itself, but this is no collectible. It’s more of a curiosity. So, I feel the tuning does nothing but enhance the value of the gun. I won’t scope this rifle because of the pristine condition, but I will leave it out of the case as a shooter.
In the future, I will chronograph and also shoot for accuracy the vintage Beeman Silver Jet pellets, which–believe it or not, started this whole report in the first place.
On Monday, I’ll show you a 124 clone Vince sent to me.
