Caliber doesn't matter anymore. Pick anything from a slingshot, Gammo air rifle, 12 guage, .22lr all the way up the ladder. Shot placement is the ONLY thing matters in todays world. At least that's what I hear.

Despite my many hours of practicing I am a piss poor shot because I haven't shot 500 elk over 50 years and every single one of them did not drop in their tracks. To make it worse sometimes I mis-judge wind and distance since I can't do trigonometry in my head, I need sctratch paper and sometimes I forget to bring it. Sometimes an animal even moves when I pull the trigger since my Jedi powers aren't strong enough to make them stay still. My x-ray vision is weak and I have hit small tree branches that I didn't see and I have inadvertanly nailed the shoulder bone in it's thickest part since I'm still learning how to curve a bullet path. I'm a wimp and sometimes I leave my benchrest in camp because it gets too heavy for me to carry and I have to shoot without it making me sometimes not perfectly steady. Hell I even have to shoot with both hands on my rifle and I cannot shoot a soda can at 200 yds and then shoot it 5 more times before it lands.

For guys like me I prefer something in the 7mm to .30 caliber range for starters. Anything bigger of course would work as well. If you're a better shot than me then just close your eyes and pull what ever you grab first out of the gun cabinet.