My thoughts are for home defense rifle you want the shortest, biggest bore possible. 12 guage fits well in that role. If it's going to be an AR out of your choices I'd pick 300 BO with TESTED ammo and mags.
I've been buying LPK from Fulton Armory for years. They have it without trigger ( I never use those milspec shit triggers) and it's cheap and always in stock. I think it's $35....and seems to be very nice quality.
Re: Oh Crap!! Round stuck in chamber
Problem is .......you're driving around with a LIVE round in the chamber and god forbid......
this needs to be handled at home and like has been said do NOT
pound on the bullet/muzzle end
be careful!
Re: 300 vs 338 and the TRG
300 WM for what you do....actually 308 or 260 even but I know how you feel. You cannot "load down" that 338 very much anyway so what's the point? The WM will do it all and IF you ever get to a longer range will allow you to strut some.