I also thought that at one point, but I don't think it's a great idea. AR-10 isn't even theoretically significantly superior to AR-15 unless you go out past 500-600m.

Real quick:

• 223 has 400fps higher velocity at muzzle. 308 doesn't catch up until past 300m.
• 223 has less drop out to 500m
• 223 has plenty of wounding potential with FMJ out to 150-200m, farther if you use SP like I do
• 308 doesn't convincingly dominate 223 except at extreme ranges like 700-1000m. No AR-10 or similar battle rifle is going to be 700m effective. Unless you build some sort of target rifle, you're going to end up with the same shitty 1-2moa performance as the AR-15 guys, especially if you shoot ball ammo like 99 percent of ar-10 guys. Also, holdover at 700m is a bitch and you're going to need a decent amount of magnification to be useful at 7-800m... all of which compromises the usefulness of the gun at short range work.
• 223 ammo weighs way less, costs less, less recoil, more magazine capacity, less rifle weight, etc

AR-15 is superior in every fucking way. If you want to punch 30 caliber holes in people at assault rifle ranges, get an AK in 7.62x39 or an AR in 300 BLK. There are heaps of great projectiles for either cartridge. With a good projectile, AK terminal ballistics are the same as any other 30 caliber hunting cartridge.

edit- oh and odds are that all your self defense scenarios will unfold at well under 200m. You'll be much better off with a light, mildly recoiling rifle with 30-40 rounds of ammo and a red dot vs a heavy rifle that holds 20 and kicks like a mule with a long distance scope.

Those aren’t cheap and neither is Ammo

Get an AR 15 it is the way.

Be aware there's no real standardization of parts compatibility and dimensions. You'll want to make sure you can get a different charging handle, replacement bolt and extractor, and spare springs at least.