The best that you can do is minimize the possibility of a slam fire. If you are dealing with a M1 Garand most of these rifles are over 75 years old. If the rifle is within functioning specification than you should be okay. Unfortunately in many cases, folks buy these rifles and have no idea how old the major parts are. Springs, firing pin and extractors should be inspected on an ongoing basis. The receiver should be inspected as well. When in doubt replace. Ammunition is the other potential problem especially military surplus and reloads. As one who reloads, I take extra care to ensure top quality ammunition is shot in my guns. My quality control starts at each step in the reloading process. Check, double check in some cases triple check the rounds. When in doubt do not use. Guns are becoming too dear and expensive to do short cuts on parts and ammunition. Please inspect your guns and ammunition, stay safe and enjoy our shooting sports.