Originally Posted by
megasupermagnum
Then why don't Thompson Center barrels shoot a patched round ball well? By well, I mean as good or better than conicals. I realize my example of 3 guns is small, but all three are marginal with a PRB. I tried smaller with thick patches, larger with thin patches, all kinds of wadding, FFg and FFFg powder from 30 to 120 grains. After an entire summer of working with a single TC Renegade, I got it to where I could count on 5"-6" at 100 yards. Many, many loads were far worse. From what I read, a good smoothbore can shoot 3" at 50 yards! I can count on any of my smooth bore shotgun cartridge guns to shoot 4" at 50 yards with a round ball.
If it were the twist rate, wouldn't you expect lower charges to shoot better? In actual practice, I could tell very little difference in accuracy with any powder charge. 30-40 grains was often the LEAST accurate. I tried pure lead, 40/1 alloy, 20/1 alloy, and COWW.
The reality is the thompson centers all shoot a conical lights out if it fits well.
To reiterate, lower charges of powder often shoot worse in TC 1:48 twist barrels. Guys that get these guns to shoot PRB almost universally use a super tight fitting combo to grip the shallow rifling. So what does that leave? Rifling depth. What else could it be?