Thats a hard one as I have had so darn many. I quess my sporterized Model 38 6.5x55 Mauser would have to be it. It grouped 5/8 of an inch with the first load I ever tried. 140 grain Hornady. I have shot about 50-60 head of big game with it and is the only rifle I own that has never even once required a second shot. Most dropped in their tracks. A couiple that I hit at nearly 300 yards ran a short ways befor folding up. I have had it for twenty years or a little more. Those were two of the longest three shots that I have ever made and don't as a rule like to even try those ranges. Many things can happen and most of them are bad.