smarquez's advice is really good. And with regard to the .223 and .300, yes they are different. But mistakes CAN happen, even to people who "have business shooting," and the steps and adherence to routine that smarquez suggested goes a long ways towards keeping a careless error from occurring. My friend and I both have similar rifles, down to the scope, one in .260 and the other in 7-08. We are very careful to remove the ammo from the bench when we switch shooters at the bench! We've also checked, with firing pin removed, to be sure the 7-08 ammo won't chamber in the .260. It won't, but we still follow our routine of not having both boxes of ammo at the bench. The other thing I'd say is to always clean ALL ammo out of pockets if you carry ammo loose.
