We shorten barrels here in England, usually to thread and fit a silencer/moderator.Our favourite length for a .22 is 14", although we get through a heck of a lot of 12" volquartsen carbon fibre barrels.We usually cut .17,s down to 16", which gives a good compromise between power and length. I cant recall seeing a .22 magnum in the shop, no one uses them here.We tend to use a standard barrel, and shorten it, to use in our fully suppressed guns.I dont know what it is about standard barrels, but out of the box 99% are poor, ME, you have a good one there, but they ALWAYS perform better, after a bit of tlc.Green mountain now do a real little beauty, its the same length and taper as a standard barrel, but it fluted, and in stainless, these little beauties really do shoot well.As for chambering, its something we generally dont touch, unless theres a problem.Strangely enough, i would say all of our customers who want a "t" barrel shortening, do it to reduce weight, but the "t" is actually, a very good barrel indeed.