Whatever you do...DO NOT GET AN AR-15!!!
If you liked Lego's when you were young, and ended up with a lot of them when you grew out of them, this AR thing will become just like that. At least it has for me.
This is my story. Like a lot of folks, I bought my first one right after our last presidential election. Then I started to change components on it. Then I started putting them together myself. Right after that, Remington came out with their R-15 in full camo! Had to have one of those. Oh! What do you mean, they make it in .204? Had to build one of those too. But wait, I really love my .17 Remington for predator hunting when the pelts are prime, and what's that? I can build one of those in an AR? Man, I lost a lot of 17 Remington brass with that one. Hmmm, what if I just neck down a 223 to 17? Oh, that's been done? Cool, I don't have to have a reamer built, and I had another project. (Great rifle by the way!) Go to thinking...it sure would be great to have an upper in a larger caliber. A guy named Mike Milli,
http://www.dtechsuperstore.com/ is a fastastic builder. Sooo, I have one in 25 WSSM. It's my favorite (at least for now). I know antelope hate it. I have a Black Hole Weaponry barrel in 6.5 Grendel that I'm building an upper on for my wife for Montana antelope right now. Which reminds me, I better get out to the shop instead of reading and typing.
I just wanted to warn you before you start down this road. If I had to do it all over....I'd do it all again!