Fist-sized groups at 75 yards is about, what, 4-5 inches. At 50 yards, those will be 2 or 3. I'd say that's pretty good already!
I'd say your patch thickness and charge is good. You could consider going up or down 5 grains for fine-tuning, but I really think your actually there.
Just practice now, and if you were shooting off bench and bags, start (and keep!) practicing from whatever positions you'll be hunting from. If you can keep those groups from seated, kneeling, and especially offhand, you're doing good.
Oh, and if you're getting good groups with PRB and your patches are "blown" or "torn"...so what! There's no harm in it, just take a little extra care to clean the lead off your lands when you're done.
I learned on a Lyman Trade Rifle that was 20+ years old when I got it. I used 90 grains FF Goex under a .490 RB wrapped in 0.010 patches. The fit was really loose and patches would come out burned in several spots (surprisingly), but dang wouldn't it group well- 1 inches at 50 yards. Cloverleaf on a good day. So...who cares if the patches burned through if your groups are good.
And like others have said if it's a new barrel, the edges of your lands will wear down after 50 or 100 shots or so and the cut patches will lessen or disappear. Don't be afraid (or worried) if they don't. I've put over 700 rounds through my .54 and one edge of one land still cuts patches...and it shoots fine.
Keep at it and good luck!