Actually .495 ball for sufficiant "Pull", two reasons, one for best combustion, second to prevent inertial creep as these guns do recoil a bit.
Local black powder smith and barrel maker does these on Remingtons and Rogers&Spencer revolvers, indeed, is making a THREE AND ONE-HALF inch .50 on a stainless Pietta/Remington (Better steel metallurgy) cylinder is 17-4PH, barrel 416R. Everybody else got a short barrel Remmie, i got one in FIFTY caliber!
NOW for those wantin a REAL big bore gun, he also does a SOLID FRAME conversion to Walker and Dragoon replicas, in FIFTY-EIGHT caliber!! Yup! Thats right! .585 groove in that barrel!
Bullet pull no problem with correct loading technique and the ballistics are...WOW! The loading he showed me in testing at shop over chronograph pushed a 440 grain bullet at 1,200fps, sorta like carryin a five shot slug gun on your hip. (And yup, expect mine in mid August!)
And cause he will NOT copy another mans work, my family collectively has THREE of the Clements conversions on order, each with an extra cylinder. And yup, coulda had a SUPER vacation in Tahiti on that money!