I was wondering what the difference is between .308 30-06 and a 30-30 ( I might of made that up)  what are the purposes of these different calibers and which is the best for taking down deer size targets.  I'm going to attempt to hunt a deer with my AR15. using 66+grain bullet.

Well, the .308 and .30-06 were both military cartridges.  The bullets they use are fairly identical, and in the military loadings, they perform almost identically.  The .30-06 is about .5 inches longer than the .308, which in commercial, or bolt action guns, can be loaded a little hotter.  The .30-30 was Winchester's rimmed cartridge that was one of the first to use smokeless powder.  It is a bit less powerful than the .308, due to reduced case capacity, less powder and lower velocity.   Any of these three rounds should work great on deer up to about 200lb plus.  

As for using your AR for deer hunting, check your state laws regarding the minimum caliber allowed for hunting.  In some states, you can't use a .22 (.223 or the like).  And in some states, you cannot use a rifle with a magazine capacity of more than 5 rounds.  

M@

Hunting can be a lot of fun when your quarry goes right down on the first shot. Unless you have a good working knowledge of what you are hunting, deer and the .223 cartridge are not a match made in heaven. I would hate to tell the story of the one that I hit and couldn't find.

30-30 is a good solid deer cartridge. The differences between the 3 is the velocity. 30-30 = 150gr 2300fps max, 308 150 gr 2700-2800fps max, 30-06 150gr 2900-3000 max. The advantage of the longer cartridges are that they can shoot heavier slugs.

Since you're up in Penna. where most deer hunting is fairly short range in the woods, I'd say either the 30-30 or the .308 would do a good job for you.  Right now the only commonly available 30-30s are the lever action Winchesters and Marlins, and if you like lever actions that's probably the way to go.  The .308 cartridge can be found in bolt action, semi auto, or pump action rifles.

I'd stay away from the 30-06, unless you find a really good deal on a used one.  It's a grand old cartridge, but for a deer hunter, it won't do anything the .308 won't do as well, and rifles for it have longer actions and tend to be heavier.