usbp: My opinion on what is going to shoot best in these guns with the 1:20 twist barrel,,, would be hotter 250 gr loads IE; Loads in the Skeeter Skelton Class of 7.5 gr of Unique with a Keith Boolit That should yield @ 800+fps from a 3" bbl.
You will need to shoot about 2-300 rounds thru it to break it in and then if it is going to shoot and you have the right boolit diameter for the throats and barrel it should be good to go. Jacketed bullets at .429 diameter are not going to shoot well if the throats on the chambers are larger which they probably are.
The groove dia., throat dia., both need to be known in order to figure out which boolit size is going to work best.
You can ask DougGuy about this, as he is the resident expert on this relationship. go back and re read Post #14.
Randy