Re: Optimim barrel length for velocity, match ammo?
Depends on what your definition of "optimum" is.
Given that your goal is to remain subsonic, plus taking into account a 22LR generates its max velocity in about 12 inches of barrel, three other factors generally drive "optimum" 22 LR barrel length:
- sight radius
- rifle balance/weight
- the tightest spot in the barrel being the last thing that touches the bullet
I own two accurate (as in one won the National 3P Championship 8 times) 54-actioned Anschutz rifles. Both have the following in common:
- 24 inch barrels
- threaded rather than pinned actions/barrels
- trued receivers
- some method of "choke" for the barrel
Rifle #1 has the end of the barrel turned down for about 2 inches, then a barrel diameter metal sleeve on the outside of it. The sleeve was made undersize. In order to fit the sleeve, the barrel was frozen, then the sleeve heated, to fit the two parts together. Once cooled they become one, while inducing choke to the barrel.
Rifle #2 has a Benchmark reverse taper barrel. The barrel is a button barrel, therefore the more metal on the outside, the more resistance the button has on pushing the metal out of the way. A combination of the lapping as well as the reverse taper result in the muzzle being the tight spot in this barrel.
If one were inclined to modify a rimfire barrel they have in hand to achieve an optimum accuracy length, the most important element in doing so would be finding the tight spot in the barrel and cutting it there.
Bill Calfee has written numerous articles on this subject, including a do it yourselfer's guide to slugging a barrel and learning what its interior dimensions are like. The bottom line is, if you have a "trumpet" barrel, that is a tight spot prior to the muzzle, your barrel has a low likelihood of producing good accuracy.