I'd recommend 1:66 unless you don't care about accuracy beyond 100 yards.
I make what is considered a decent Brown Bess replica
but i've taken the twist from 1:48 ....
At 200 yards it doesn't much matter how good your eyes are, a roundball will be inaccurate. The ballistic coefficient is just too small.
Even with a good round ball twist 1 in 70 in a 50 cal ...
I`ve tested 3 different rifles with this twist and every shot past 100 yards would start to drift right or left depending on the rifle ...these were match grade custom built rifles .they were tack drivers to the 100 yard line ...but the drift set in at 110 yards .
I`ve never done this testing with a 1 in 48 twist ...but have owned several and they were good shooters out to 100 yards I just never benched them at that distance .
Well, you know, I've heard that before, but I've also heard that during the War of Independence, those Pennsylvania rifles were deadly at 200 yards and beyond. Now, I don't know if they used crossed sticks or what, but I've always heard that a 1:66 twist will give you better accuracy at a greater distance than a 1:48.
I just can't believe that all those stories about the Pennsylvania rifles during the Revolutionary War were tall tales.