Re: 7 MM Remington Magnum
Any of the magnum belted case cartridges can suffer very short case life. Here's the problem:
The belted cases head space on the belt, not on the case shoulder as rimless cases do. Manufacturer tend to give a bit too much room for the shoulder when they cut the chamber for these magnum guns. When the cartridge is fired the body of the case stretches to meet and fill the chamber The case tends to stretch just forward of the belt. During reloading the shoulder is pushed back, working the case. The next firing results in the same case stretching and after a couple of reloads you start to get head separations or case splitting. This severely limits the number of times the brass can be reloaded.
The trick to get more reloads out of belted cases is to use the first shooting to fire form the brass to the gun you are shooting it in. Then when you size the case, back the sizing die out of the press just enough so the shoulder ends up after sizing in the same place (less a couple of thousandths) that it was when it came out of the gun. For repeated reloading of the cases you should do the same again. With this approach you can get reasonable life from the belted cases. BUT..... these cases will only fit the gun they came out of and probably no other gun (like your buddies identical version).
If you don't care how often you have to buy new cases then just disregard this approach.