breech seal shimming headsup

[john]

i have touched on this elsewhere
www.gatewaytoairguns.org/GTA/index.php/topic,14487.0.html re gap entitled "Breach seal shimming questions"
but it is not common knowledge and should be as it can save alot of unnecessary heartache and fruitless maintenance. To be clear for noobs, this is about the breech seal, not the piston seal.

If you observe that your breech seal is not evenly proud all the way around, do not be alarmed. The channel it lives in is not evenly deep all the way around. Like a swimming pool, it has a deep end and a shallow end. The change in breech seal channel depth is ~1thou. That is not an accident. It's not a manufacturing defect. It is a design feature. So because the seal IS of uniform height around ITS circumference BUT sits in the sloped channel, of course it is going to stick out further on one side, namely the bottom.

Why isn't this well known/publicized and why does it make sense?  Answer to first, ignorance and/or apathy; answer to second, obvious if you examine the breechblock-to-transferport gap. By the term gap, I do not mean that there is or ever should be a parallel gap between the breechblock face and the transfer port face. When the barrel is locked up, properly locked up, the top of the breechblock and the top of the port face are touching and touching firmly and touching consistantly on every shot. If not, The seal is not the answer to that issue. That is an alive-jam/detent marital issue which you need to address. Counseling is available. So, clearly, there should be no gap at the top EVER during lockup.

But there is a gap at the bottom. So the space between the faces is pie shaped. It is a stingy sliver of pie but it is there. This is why the seal protrudes further on the bottom than the top, in order to fill the pie-shaped gap. Do not shim this out by shimming only under the top of the seal; you will be defeating the purpose of the seal channel designed-in slope.

I am not saying do not shim. But if you shim, shim uniformly. Also, if you shim, do not shim in an attempt to solve a perceived lockup problem. Shim to address seal leakage. Test for leakage by shooting in a safe manner with powder on top of the seal...baby power, foot powder, talcom powder, flour from the kitchen cubboard, totally whatever. Then turn the gun upsidedown and repeat to test the bottom of the seal. Or grab a Kleenex, split the layers, put a half inch square of that over the transfer port face, shoot safely thru it, check for tears.

Hope this helps. Have fun. Be safe. Slow down. Haste is the common denominator of all accidents.