A 30-30 is plenty for a mule deer I know folks out here who hunt elk with a 30-30, I personally use a 30-30 occassionally for whitetails mainly when in thick woods and shots are under 75 yards. I use a handload in mine pushing a 150 grain Barnes X bullet every deer I ve hit with that barnes bullet usually didnt get very far before folding up an falling over the furthest I had one run was roughly 40 yards. I'v had deer run further after being hit with a .308, A fews years back I double lunged a buck at 25 yards hit him square in the shoulder with my 308 he ran 200 yards on 3 legs down the logging road from where I shot him. earlier that morning I shot a doe with my 30-30 hit her square in the shoulder at about 50 yards she took 2 steps and fell over like like somebody pulled the battery out. The only times I have ever dropped a deer in their track was with a CNS shot, killed 2 like that with a .223 rem at roughly 100 yards.