I have three original mountain rifles. Two have straight barrels and one is swamped. The swamp is not as obvious as todays barrels, but it is swamped. I have used "A" weight for .32 and .40 cal rifles and they came out well. Also, I have used "B" weight swamped barrels on .45 with good results. However, I have also used straight 13/16 barrels for .40 and .45 cal rifles with good feeling rifles coming out of the builds. Currently, I have been using 3/4 barrels for .29 and .30 cal rifles resulting in slim good feeling rifles. Good luck with your build.
Roger Sells