IMO, the MGI RRB would be the best thing that you could put into that 45ACP gun.
It works great with 45ACP and also with any other caliber that I can think of for the AR15 platform. It is basically a "universal buffer" that really performs super with all the calibers.
It is about 7.1 ounces, but it has the recoil taming ability which other heavy buffers do not have.
It will drastically reduce the impact level of the buffer against the Cav Arms butt, and also your shoulder.
You'll love it.
Guaranteed, or your money back!