Re: Length of barrel
Start with a 38" barrel, shoot it till you think it's not shooting very well anymore, cut off 3" of barrel at the chamber end and rechamber and rethread and start over again.
That way you will get into good rifling again.
Normally, if you get 2000 rounds the first time and it's set back and rechambered, expect 1/2 life or 1000 rounds out of it the next time. That's the way it usually works but, not always.