I'm going to be building my first AR lower in a couple weeks, the stock, grip, and buffer tube are on their way, and now I'm having to decide what upper I'm going to put on it. I've been thinking about a .300 blackout build because of it's superiority over the .223 inside of 300 yards and it supresses well. But there's some things that have given me pause at least for the time being. I'm under 21 so I can't build it as an SBR or order a suppressor which takes away two of the advantages BO has over .223 and I'm planning on getting a Keltec sub 2000 in .40 cal which covers a lot of the same ground the BO does, is also fairly easy to suppress down the road, weighs under 5 pounds, and can be folded so it can be stored in a smaller space (which is useful for me as I live in a tiny house so space is paramount). On top of those reasons BO is also more expensive to shoot then .40 S&W or .223 because I don't reload. So what do you all think does it make sense for me to build a 300 BO AR now or should I get a standard .223 upper now and wait a couple years to build a 300 BO SBR later. Primary uses would be target shooting, 3 gun, home defense, and maybe some coyote hunting.