I guess I should have said "standard" instead of "mil-spec." Anyhow, I got an email from Ruger in which was said that Ruger lowers are standard. On the other hand, Ruger uppers and bolt assemblies are not, I believe. The Ruger firing pin is not interchangeable with other brands' and I read somewhere (but I may be mistaken) that the carrier is non-standard, either. Maybe Ruger wanted to prevent basement tinkerers from trying to make the AR 556 into a full-auto gun. Maybe. I don't know enough about AR 15's even though I have three of them: a Colt Sporter post-ban, dehorned, the Ruger, and a S&W M&P 15. When I bought a Bushmaster upper with a 24" fluted barrel for my Colt, I had to buy an offset hinge pin because the Sporter's pin did not align with the new upper. I wish those who make AR 15's all remained within the same specs as everybody else's.
Thanks for the answers. I am waiting for a new credit card that will give me $250 if I charge on it $1000 the first month, and as soon as I get the card I'll order the .50 Beowulf with the fixed muzzle brake, a 10-round magazine, and a few boxes of ammo with the Hornady XTP bullets. I want to use this caliber on hogs and deer. I have been using a Ruger M77 in .338 WM but it's too long and cumbersome in a blind and all my shots at the deer I've harvested these past five years (9 whitetails) have been between 10 and 90 yards.