Using Once-Fired Military Brass
Assuming we have a batch of NATO ball cases, here are the steps to get it ready for use:
Inspect the cases, and throw out any with serious damage to mouth or rim. True up out-of-round case mouths with a tapered punch, such as a nail set, so they will enter the sizing die smoothly.
De-prime with a Lee or RCBS de-prime die. Then clean well in tumbler or vibratory cleaner for several hours. All the dirt and grit must be removed to avoid damage to sizing dies.
If the cases were fired in a loose chambered rifle, or a machine gun, a regular sizing die may not reduce the base diameter enough to chamber in your rifle. The thicker web and case walls spring back more than civilian cases. We usually don't know what sort of gun or guns the brass came from, so it's best to return each case to minimum dimensions before loading and firing the first time in your rifle. Lube the cases well, inside and out, and size in a special small base die. I share small base dies with other shooters. Clean again to remove sizing lube. Trim to length, then chamfer and deburr case mouths.
Ream or swage out the primer crimp. Reaming cuts away the crimp, using an inexpensive hand tool. Reaming carelessly can result in an oversize or oval pocket. Swaging moves metal out of the way, and slightly work hardens the pocket area. Swaging tools (RCBS is adequate, Dillon is superb) are more costly and complex, but once adjusted do a better job than reaming. Use a case mouth chamfer tool to put a light chamfer on the pocket to ease entry of the new primer.
For best results, use a flash hole reamer to remove
internal burrs. A primer pocket uniformer will also
help insure consistent ignition by making the
pockets of equal depth, and flat on the bottom.