My dad recently gave me a marlin model 39 that he found in his house when he moved in. It is in great shape except for the butt plate being cracked. I have shot some 22 long (720 FPS) and some 22LR subsonic (1040 FPS) that a local gun shop told me would be OK for this old rifle. My question is what is good to shoot out of this. I know I can't shoot high power 22LR but what is high power exactly? This is a nice old rifle and I don't want to damage it but still want to enjoy it, it's a blast.