Mart- do not worry about a REALLY slow twist for round balls. Having been involved in ML rifles for decades, we've found a 12 bore will shoot with amazing accuracy, with round balls with as much powder as your shoulder can stand with as quick as a 66" twist.

One shooting buddy of mine, when seeing my 14 bor0 rifle, had my bro make him an 11 bore Purdey style rifle in - .75 cal.

He started off with a thickly patched 575gr.WW round ball (.735") and 200gr. of powder, just over 7 drams. It shot with good good accuracy right off the bat - 3" at 100 meters, elbow resting off the pickup hood. Over the years, he reduced the load to 120gr. just to keep the balls inside the moose, with little or no loss in killing power.

That rifle has 'collected' a couple dozen (or more) moose over the years and oft times, it's the only rifle my friend uses, for moose when on group hunts with family. It is effective.

As well, the 66" to 70" twist will shoot short conicals just fine, but - round balls are where IT'S at.