Daryl- That should work with right reamers and tools to do it.
Rifling buttons or a cutter that big, I can't find reasonable.
I was thinking of screwing a rifled choke in the stepped up area
on the end that I now use as internal brake expansion area, with
the ports..But I like the ports and the hollowbase slugs should be
75yd accurate based on preliminary tests with them. And the Lyman style
slug that I will get mold done for, will be better yet.

Here is my 12GA FH Savage 210 with thumbhole
stock, I put on in place of first one that cracked.
Along with weight and heavy barrel handles recoil
great. It is a Boyd and came inleted for Savage
112, and I re-did inleting to fit 210 and
heavy barrel,and got rid of monte carlo
outline.Ed