Put this in your "for what it's worth" drawer. I bought a Kimber Rimfire Target conversion kit for my Kimber Stainless Gold Match II. Kimber recommends CCI MiniMags, a 36-grain or 40-grain copper-plated bullet at 1,260fps. I have several bricks of Federal load #712, a 38-grain copper-plated bullet at 1,260fps on hand, so I used that. The slide would not travel rearward enough to eject empties and feed fresh rounds, so I called Kimber. They thought my ammo should work fine in the kit and asked that I send it to them.

I did and they called to tell me it worked fine for them. We discussed ammo again and they said if it still didn't work right, I was to return my gun with the kit installed.

It didn't function any better but before returning it again, I bought a box of CCI MiniMags to try. They work flawlessly! I can only assume, and Kimber agrees with the logic, that the CCI ammo uses a faster-burning powder that generates enough pressure in a 5" barrel to cycle the action while the Federal ammo with identical ballistics might use a slower-burning powder more suited for rifles.

Long story short, a consistently complete powder burn usually yields more consistent velocity and better accuracy.

Ed