I had my .22 Mag cut down to 18" to keep the over all package maneuverable. Had a .17 HMR barrel cut down to 18" too, for the same reason. I don't have my Spectre yet though, so have not shot either of them since the chop and thread. But I don't expect to lose much, if any velocity, from those rounds, at 18". I'll clock 'em and see if the suppressor ever gets out of jail, maybe another month or so, maybe...
My centerfire barrels, I had some cut short for over all package length, others I've left long because I couldn't bring myself to give up the velocity. So far, all I've used is one I had cut to 19" (from 25"). It lost 240 fps with the chop. But, for that one, it's been worth it to me, I like that it's only about 1/2" longer now with the can than it was before. It's a .20-250 and still launching 39 BK's at 4000 fps, so still pretty flat and so far on a dozen coyotes it's been killing well.
- DAA