Lemme run this by ya....

[MADDOG]

Also for consistency make sure your inner barrel is shimmed tight against the outer barel so that it does not move around shot to shot. This will improve accuracy and consistency.

If you can move your inner barrel around inside your outer barrel at the "bang bang" end of your gun you need tofind a way to make it stay in one place or the vibration from firing will cause inconsistencies in shot to shot placement

[Rusty Lugnuts]

Most builders will agree that- all else being equal the stronger your spring , the sooner you have a break down. Air still being "pumped" after the bb has left the barrel means that your only using part of the piston stroke to propel the bb. Therefore your using a stronger spring than necessary to achieve your desired FPS

[Jbone 11 11]

Originally Posted by MADDOG

Also for consistency make sure your inner barrel is shimmed tight against the outer barel so that it does not move around shot to shot. This will improve accuracy and consistency.

If you can move your inner barrel around inside your outer barrel at the "bang bang" end of your gun you need tofind a way to make it stay in one place or the vibration from firing will cause inconsistencies in shot to shot placement

Good point. I've often thought about this...Any tips on what to use or is it pretty much what ever works?

[ccyg8774]

Originally Posted by Jbone 11 11

Good point. I've often thought about this...Any tips on what to use or is it pretty much what ever works?

Rubber O-ring(s) in the space between the outer and inner barrel.

[ThunderCactus]

Teflon tape. It's very thin, naturally extremely low friction, has some squish to it, and very stable for very little tension.
You can effectively shim the inner barrel to the outer barrel with teflon tape, whereas with O-rings you just really on compression. Either method has the same result, teflon tape is just easier to work with after the fact