Who makes the strongest upper receiver?

[Drifter]

Watch out with the MUR. I've heard of the FA falling off (it's just pinned on). I'm avoiding it for that reason.

If you're not worried about the FA, nevermind.

I would think that is very much the exception and not common at all. Even Noveske often uses the MUR.

Besides, lots of parts are pinned on an AR. Heck, the upper is pinned to the lower. :p

If it matters, the MUR's FA can be removed and a flat plate used instead if desired: