30.06. This was this first gun to take a Grand Slam, every species of big game, in North America. It has killed every animal I can think of also. You can buy rounds from a 55 grain Accelerator to 220 grain soft point. Federal and Hornady make a "magnum" load for .06 from 150-180 grain. I use the 180 on everything I hunt. It ballistically turns the .06 into a .300 mag. Same energy and velocity. You will always have people claiming their 7mm, 300, 338, 3006 etc are best but the one thing you MUST remember is it is the SHOOTER not the GUN that makes the shot and the kill. I own two .06 and have shot a half dozen 7mm and bigger. None have impressed me as much as the versitility of the .06. You can also buy 3006 ammo just about anywhere you will hunt. I have seen it in gas stations with a few boxes of 12ga and some .22's. No other rounds though. I would buy a bolt action since they are the easiest to shoot and maintain. Good luck and staight shooting.