by Tom Gaylord
Writing as B.B. Pelletier

Rail Lock Compressor R8

The Beeman R8 looks like a baby R1.

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6

A history of airguns

This report covers:

  • New mainspring
  • The compression chamber honing
  • The Rail Lock Compressor
  • Cleaning
  • Piston seal
  • Installed the new seal and mainspring
  • Back in the stock
  • Cocking effort
  • RWS Hobbys
  • RWS Superdomes
  • JSB Exact RS
  • Firing behavior
  • Conclusions so far

The new mainspring and piston seal Pyramyd Air sent for my R8 arrived and I installed them last Thursday. This will document how that installation went and look at the velocity results, plus the powerplant smoothness.

New mainspring

The new mainspring is made from better wire than the stock Weihrauch spring. Gene Salvino has reports of guns with up to 9,000 shots with this spring that have lost little velocity, if any, since installation.

I knew there would be a lot of interest in this mainspring, so I examined it carefully and also photographed it next to the existing spring. The new spring wire is silver colored, where the Weihrauch spring wire is a darker color. The new spring appears to be about one inch longer than the original, but I don’t think it has been scragged.

Scragging means leaving the spring fully compressed for a length of time (4-8 hours) to shorten it to its operational length. This will happen while it is inside the gun, so except for the fact that it is longer and needs to be compressed more to install, there is no problem. However, I did show you years ago how to scrag a mainspring if you need to.

springs
New spring on top. Both springs are the same size, except for the length of the new spring.

Both springs have 30.25 coils of wire that is 0.120-inches in diameter. And both are ground flat on both ends. So they have the same compressed length. The new spring will eventually become shorter just from being under compression inside the rifle. I examined the new spring under 10X magnification and it appears to have been shot-blasted by very fine media. The Weihrauch spring under the same magnification appears smooth.

The compression chamber honing

This was a difficult picture to take, but I was able to get a photo of the start of the compression chamber. You can see the honing that runs around the inside of the chamber, perpendicular to the axis of the piston’s travel.

honing
The arrow points to the start of the compression chamber. The crosshatch honing from the factory transitions to circular honing in the chamber where the arrow points.

Lighting that photo was extremely difficult, but you do get to see at least a small part of the circular honing I have talked about. That pattern is not correct, and we will see what effect it has on velocity, if any.

The Rail Lock Compressor

With the longer new mainspring I had to adjust the Air Venturi Rail Lock Mainspring Compressor out an extra inch, and it barely fit. Also, it had to push the mainspring in that extra distance to get the end cap to meet the threads in the spring tube. It was harder to do, plus the white Nylon tip did walk around the end cap as I compressed the spring.

When the end cap was finally up to the threads I thought it would be difficult to get the threads started, and in truth it was harder than before. But I used a rubber hammer to move the end cap slightly until the threads seemed aligned and they did start. It took me maybe five minutes of fiddling to get the threads started this time, but I think the same would be true for any mainspring compressor. Maybe if the white tip at the end of the threaded rod turned freely it would have gone easier, but that would be my only observation.

Cleaning

I spent a lot of time cleaning all the grease from the action. When I was finished surfaces were dry and ready for the new parts. I probably spent a half hour just cleaning the gun.

When I removed the old piston seal there was old grease underneath. I dried the end of the piston and thoroughly cleaned the inside of its body with paper towels and cotton swabs.

I cleaned the inside of the spring tube and compression chamber again with paper towels on the end of a long dowel. This area was already pretty clean, except some of the grease I had applied in my previous tune had gotten onto the surfaces. When I was finished, the inside of the tube was dry.

Piston seal

The old piston seal was very soft and pliable. There is a small imperfection at one spot on the outer edge that the new seal doesn’t have, but I don’t think it caused any problems.

Installed the new seal and mainspring

I know I said I was just going to install the new seal and see how the rifle performed first, but after seeing how the new mainspring compared to the old one, I couldn’t resist installing it. I greased the new seal and back end of the piston with white lithium grease. I also greased the new mainspring and the old spring guide with the same grease. I kept the amount of grease low, but all metal surfaces were coated. Lithium grease is thin, so I expect no velocity loss from what was done.

I checked the fit of the new mainspring on the spring guide. One end of the spring was tight on the guide, so that was the end I used. The new mainspring fits the inside of the piston ever-so-slightly tighter than the factory spring, which should help reduce vibration.

Back in the stock

The entire job took 2 hours, which included time to take pictures and to clean the parts. Then I put the barreled action back in the stock. Now it was time to test.

Cocking effort

With the new spring the rifle now cocks with 30 lbs. of effort. It certainly feels heavier to cock than before, which was measured at 25 lbs.

RWS Hobbys

Okay, here we go with the velocity test. First up are RWS Hobbys, which are light and should be fast. The R8 was rated at 735 f.p.s. when it was new.

Before tuning…….First tune………Second tune……..Today

Vel…….Spread….Vel…….Spread…Vel….Spread….Vel…….Spread
523……..27……..402……….64…….416……47…….741……..18

The velocity with Hobbys averaged 741 f.p.s. The spread went from a low of 732 to a high of 750 f.p.s. At the average velocity this pellet generated 8.54 foot pounds of energy at the muzzle. This R8 has obviously returned to factory performance with the installation of the new Beeman mainspring and piston seal.

RWS Superdomes

At 8.3 grains, the RWS Superdome pellet is on the heavy side for the R8. Let’s see how it did.

Before tuning…….First tune………Second tune……..Today

Vel…….Spread….Vel…….Spread…Vel….Spread….Vel…….Spread
503……..32……..445……….13…….NA……NA……680……..18

Superdomes averaged 680 f.p.s. in the R8. The low was 671 and the high was 689 f.p.s., for a spread of 18 f.p.s. At the average velocity this pellet generated 8.52 foot-pounds at the muzzle.

JSB Exact RS

The last pellet I tested was the 7.33-grain JSB Exact RS. This should be idea for the R8’s power.

Before tuning…….First tune………Second tune……..Today

Vel…….Spread….Vel…….Spread…Vel….Spread….Vel…….Spread
645……..29……..582……….18…….NA……NA……666……..31

RS pellets averaged 666 f.p.s. They ranged from a low of 654 to a high of 685 f.p.s. At the average velocity they produced 7.22 foot-pounds of energy at the muzzle.

Firing behavior

The R8 shoots smoothly. A tiny but noticeable bit of vibration has crept into each shot. It is not bothersome and I actually have to feel for it to know it’s there. I can tell the rifle isn’t as smooth as before, but it’s 100/200 f.p.s. faster which I will take.

I think as this tune settles in the cocking effort will lighten just a bit. I doubt the slight vibration will ever go away. I could give it a shot of Tune in a Tube, but it isn’t unpleasant enough to warrant that, in my opinion.

Conclusions so far

My concerns about the compression chamber honing appear to have been groundless. That’s very comforting, because it means I can stop chasing that gremlin.

I could go farther and give this rifle a top grade tune with piston button bearings, a custom fitted spring guide and a piston liner to remove all vibration, but that doesn’t seem suited to the R8. Instead I will keep it as it now is and shoot it whenever I want a nice lightweight accurate pellet rifle.

I’ll probably do one more accuracy test — just so I can shoot the rifle again. Maybe I’ll back up to 25 yards, but I think I’ll still use the iron sights.