Breech seal test?????

[tjk]

I've heard of testing the breech seal with a peice of paper of something similar, but how exacly do you perform this test? You see, I shimmed the seal (the seal was almost totally flush with the breach)on my GF's rifle and shot it for a while, then took the shim out, replaced the O-Ring,and "BANG" the gun said. It didn'tdetonate (no burning smell) , but there was very heavy dieseling down the barrel. Hope I didn't ruin the seal!!!!! The spring cocks just as smooth as it always has so I think we're ok with that. A chroney is definatelly on my wish-list from Santa.tjk

[shadow]

If you think that your losing compression out of the breach area lay a piece of tissue over the breach area when your ready to shoot. if the tissue blows off that area, your losing compression through the breach seal. Ed

[tjk]

Thanks Ed. Sounds simple enough to me. But what would cause it to diesel so violentlyafter I removed the shim?!?!?!? Could it have leaked with the shim in it before and not realized by me? I figured the shim would have sealled any possible leak. Wonder how this may have effected the resistance of the pellets with and without the shim. Still got lots to learn! tjk

[shadow]

Did you lube tune it? might have a little to much lube which would cause the excessive dieseling. Run a swab down the barrel and see how dirty it is, that would also show you if the lube is building up in the barrel from a overlube tune. We'll get it figured out. Oh do you have a chrony? that would really help us find out what's going on inside. Ed

[shadow]

let's help get this problem fixed for a family member.:) Ed

[dave2288]

maybe the seal without the shim does such a bad job that it lets lots of air out at the breech, causing piston slam?

i think this would be more of a ? for the tuners/machinsits out there...wonder when they'll respond to this...soon i hope for your sake

[davee1]

I've done a lot of work with the breech seals on my guns. You describe symptoms that I have experienced when my breech seals are leaking. Its good that you want a chrony because it is a very valuable tool. When there is enough of a leak at the breech seal, air compression suffers and among other things...it causes piston slam, poor velocity, and deiseling. When the breech seal is shimmed, then you get the proper fit/seal, and everything goes back to normal. I think you should put your shim back in, and get a chrony. Once you've got a chrony, then you can experiment with different thicknesses of shims until you get the optimum velocity going on.

[tjk]

Thanks Dave and Davee, and Ed for your input on this matter. Great feed-back, and probable causes to this situation. I do plan on getting a chroney real soon. The shims back in, and the rifle shoots like normal, but until I get a chroney, I won't know if the performance has dropped off. When I get one, I'll post some results and let you know where we stand. Thanks again fellas, Thomas

[davee1]

You may already know this...but just in case:

There is a sweet spot when experimenting with breech seal shimming. There is a point where more shimming creates no more gain in velocity/consistency, and there is a point where less shimming creates a loss ofvelocity/consistency. The sweet spot of course is in between those two points, and where lockup is not affected. Takes a lot of time and patience to get it right, and the value of a chrony becomes immediately evident. But it is actually quite easy.

My Beeman .22 RS2gained 44fps with.22 RWS Hobby pellets. Started out at 746fps and ended up at 790fps. I neglected to document the consistency, but it was really good. Thats just one example, andalmost every airgun I have benifited from breech seal shimming.

[gamo2hammerli]

I just use the primative way.....tissue lying on top of the breech gap with it's sides hanging down.  If the tissue puffs up or out...then the seal needs looking at.  If it happens to blow air out underneath.....I'm out of luck.  )