Had several Herrett barrels over the years....none had what I would call lazer sharp accuracy(.50"-.75" @ 100yd), but all shot good(1"-1.5" @100yd). From the late '70's to early '90's I shot nothing but 110gr Sierra and Speer and WW680. Winchester brass primarily and a duke's mixture of LR primers. Nosler came along with 125BT's in the '90's and if anything accuracy improved slightly. I never played with heavier bullets, probably because I also had a 357Herrett and later on a 14" 30/30AI. Most of my experience was/is with 10" tube. I have tried a little AA1680, just because my hoarded supply of WW680 is dwindling(I've only got a couple of lbs. left)and although it didn't shoot quite as good, it was close.
I'd check the crown on the new barrel, condition of bore, make sure the forend fits properly(try floating it off the barrel). Since you've shot a Herrett before, I'm sure you know about headspacing, although that's more an ignition issue than accuracy.
Walt
