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Discussion Starter · #1 ·
So I shimmed the gas cylinder on my Polytech, and got the gas cylinder lock to start getting resistance at about the 4 o'clock position, then placed the upper back into the stock and installed the trigger assembly, and then fully tightened the lock as per the instructions in another thread here in the forum (I had to use the my gas cylinder wrench to get the lock to line up with the cylinder). My question is: now the front stock ferrule has no play whatsoever like before the shim was installed. Is this normal after shimming? If I use the smaller thickness shim than the lock barely has any resistance by the time I get to the 5 o'clock position, or is the smaller one the shim I should be using?

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If I'm understanding your problem and it's any help, a condition you DON'T want is the barrel band wedging against the stock ferrule. You DO want a shim that leaves slight (1/32" is enough) clearance there but still allows you to tighten the gas cyl firmly against the barrel's shoulder to take out band slippage. If you can't get there with the shims you've got and you have a wooden stock you can tap off the ferrule and trim the lip of the wood ever so slightly with a flat file, trim the rear end of the ferrule to coincide, slip the ferrule back on and try it again. If you get eggroll this time, glue the ferrule back on and complete your assembly. That's without doing any filing or cutting or time-eating futzing around with the wood at the rear of the ferrule and messing up your stock's finish.
 

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Discussion Starter · #4 ·
If I'm understanding your problem and it's any help, a condition you DON'T want is the barrel band wedging against the stock ferrule. You DO want a shim that leaves slight (1/32" is enough) clearance there but still allows you to tighten the gas cyl firmly against the barrel's shoulder to take out band slippage. If you can't get there with the shims you've got and you have a wooden stock you can tap off the ferrule and trim the lip of the wood ever so slightly with a flat file, trim the rear end of the ferrule to coincide, slip the ferrule back on and try it again. If you get eggroll this time, glue the ferrule back on and complete your assembly. That's without doing any filing or cutting or time-eating futzing around with the wood at the rear of the ferrule and messing up your stock's finish.
Sorry, got the names mixed up. You're correct, what I meant was the front band no longer has any play. I can still slide a piece of paper between the band and the ferrule no problem.
 

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Sorry, got the names mixed up. You're correct, what I meant was the front band no longer has any play. I can still slide a piece of paper between the band and the ferrule no problem.
That's how it should be. GI2
 

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Hope these help:

Shim placement



This is about where you want it after the shims are installed, just snugged up by hand here:

 
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