Steve, I have been calculating the specifics of this breech loading bullet barrel and here are the specs I came up with .... .

30 inch barrel
1 1/8 to 1 taper
4150 steel
.620 bore
1-38 twist
.004 deep rifling
.180 grooves
.060 lands
radius on the inside corners of the grooves
round the corners of the lands

I think I have covered it all, let me know if I need to change anything before sending specs to barrel maker, Thanks, I appreciate your help, Ed