58 cal. Conical Question

[DCAN]

I'm trying to decide on a caliber for a build. Torn between .54 and .58. Barrel twist will be 1-66. Does anyone have experience with a 58 cal conical which will shoot in that slow a twist. I'll be casting my own.
Thanks, Doug

 

[new2bp]

A twist that slow will be best with PRBs...

 

[RjSixgun]

I have nothing but 1-72 barrels and they shoot minie balls quite well.