I'm not sure it matters as long as it is somewhere between 1-48 and 1-72...I'm in the camp that thinks, deeper, cut rifling makes the difference...When I had Ed Rayle make ma a barrel for my .54 flinter I made in the '80s he went with a 1-72 and .015 deep rifling...It shoot lower charges quite well, 50 grains is my target/squirrel load and when it comes to hunting I have settled on 80grs FFF Goex...I started with 120grs FF Goex years ago but started backing down and found that 80 killed and grouped just fine, with less fouling...

I would suggest going with .012-.015, cut rifling, and simply with what the maker recommends, so if a problem did arise, he would be more likely to ship another one...

Something else that seldom comes up, I have a 38 inch barrel on my flinter...I'm guessing with a Hawken styled gun that you are going with a 30-34 inch barrel...With a shorter barrel, I'd lean toward a little faster twist...I'll bet the 1-60 would be just fine...