Re: spikes tactical st22 , can I shorten the barrel ??
Sure ... since the 22 doesn't rely on DI like the 5.56 you have no gas port issues. It's simply blowback. I've seen some 3-4" but you want enough to get at least some decent spin if you're going to suppress it.
I have a 7" suppressed on a M16 I built and it runs fine. Cycles ok w/out the suppressor too.. the 22 blowback is a very simple design.
Good luck
DREZ