We have done some serious varmint shooting with the 6 br in the past. P, dogs, jack rabbits, Chucks, ground squirrels. A friend sat an NBRSA Record with a 6 BR his on 60g bullet at 3700 fps, Gene Harwood. Gene had a fit when he saw me shooting 322 in my 6 BR. He insisted that I try H335 with a 71/2 with 60g sierra's on my next trip. I worked up a load when I got home with the 60's shooting match winning groups with H335 at 3700 out of a 24" barrel in a 12T. Typical cleaning frequency is 300 rounds with H335 and AA2230, 125 rounds with H322.
We had several other Hart barrels chambered up with a 12 Twist, 30" long, some max heavy varmint and some un-turned blanks. 60g Sierra' were chugging along at 3900 with tiny, tiny groups. Accuracy in the calmish wind was round an 1" at 300 yards. Barrel life was nothing short of amazing.
55g Nosler came out, we tried AA2230 with 7 1/2, now there is a marriage made in heaven at 3900 fps.
Rabbits were as far as we could see in the edges of the alfalfa fields, and 70g Sierra Blitz, TNT, and ballistic tips did a very fine job with H335.
Accuracy with 65g V max was in the 2's, and is a good compromise between the 60 and 70g bullet.
If you will stick with ball powder, don't be surprised if you get 6000-8000 rounds of accuracy in the 3's in the later part of the barrel life. We abused our barrels. Cooled with water down the barrels constantly. There were so many rabbits, we would shoot till we could not see out of the scopes, then put that rifle in a cleaning rack, then shoot another one. When all 4 were hot, we cooled them all 4 at the same time, partner did the same.
There were so many rabbits, we would dump out a box of 50 and fire as fast as we could lock and load. The Farmer told me he was in his last year if we could not help him with the rabbits. Later, he thanked us and asked how much he owed us for saving his ranch. We made 4 two week trips up there. Rabbits were eating the bottom of the hay stacks down, then the stack would fall over.
Partner and I carried around 1000 rounds of center fire for each rifle, then all our lead shotguns shells left over from duck hunting, and a bag full of pistols for close shots.
With the standard 6 BR, the 55g at 3920 fps is one heck of a varmint round. 65's were doing in the 3650 area, with 70g doing in the 3450 area with long barrels.
All barrels had zero freebore, no turn neck.
Next was a 6 BRX with all the same bullets, add 150 more fps.
Concerning barrel life, if you order enough straight on the shank of a blank, you will get 1-2 set backs gauged by over size reamer pilot pins. Don't wait too long on the set back. Unturned blanks that start off 31" give very, very good service in many thousands of great barrel life.
H335 and AA2230 does not burn up 8" of barrel life like some powders, nor fire crack them. I monitor the leade growth, set them back before the leade is moved too far forward.
For a live varmint round, 6xc or 6 X47 with 80g Noslers , AA2700 would give blistering velocity and accuracy.
If you want a live varmint rifle, please get a chamber set up for .030 freebore MAXIMUM.