The company that supplies some of the parts for Ruger also supplies them for the BFR...and they are identical.
I roll my own, too. I shoot some of the more exotic stuff (.416 Rigby and a .500 Nitro, both No. 1's, and 2 FA revolvers, .454 Casull and .475 Linebaugh....and Donna's .375 H&H) and it's the only way we can afford to make 'em go bang.
Rick