It's a 1" x 33" x 1:70" Flint round ball barrel with very deep grooves and probably the most accurate barrel I have...point and shoot and it just seems to find it's way into the bullseye...incredibly accurate.
I made several trips to the range trying 80, 90, and 100grs Goex FFg + Hornady (and Speer) .570/270grn ball (+ wonderwad + .018" pillow ticking).
All are equally accurate, settled on 100grns for a deer hunting load and will use it this fall...it's a powerhouse caliber in a tack driver barrel...and I can't imagine anything I'd hunt in north america that a 270grn round ball won't take
STOP IT! I DON"T NEED ANOTHER RIFLE, ESPECIALLY IN A NEW CALIBER! YOU'VE GOT THE WHEELS SPINNING AND THE NEXT THING WILL BE LOOKING ON LINE FOLLOWED BY TELLING LIES TO THE OLD GIRL ABOUT LONG SKINNY PACKAGES ARRIVING IN THE MAIL... A POX UPON YOU FIENDS!
There. That said, do those GM barrels drop in w/o need of further fitting? Would you know if they carry drop ins in .58 cal. for flinters?