Another way that I put a 12ga rim on
bmg case is to use the new Magtech brass
12ga cases made by CBC in Brazil.
BPI and others sell them for less than
a buck each. Being so short they aren't
in the 12ga FH category of generating power.
But you cut them off a quarter inch long, and
turn a BMG rim down to .715 diameter, push on the
Magtech base, with JB weld in the Magteck
base, and set up a squeeze collet to
crimp the Magtech base sides into the BMG
extractor groove. Crimp it in hard and tight.
And it uses large rifle primers.Fed Mag 215 best.
Other bmg case work needed is to put a chamfer
on the bmg primer pocket and drill out the
bmg primer pocket straight so that there is no
block to the primer gases coming out through the
Magtech flash hole. Chamfer back of rim a little.
These will handle
20,000 psi loads.Ed