Forgot to mention that I prefer 5 or 10 rnd. mags for all my Ar's..because I am almost always shooting from a bench.
The 30 rnders are too long, when using a 6"-9" bipod ( have 'em on most my AR's ) 30rnd mags hit the bench, forcing the barrel downward..
unless I pull the rifle back, so the mag is hanging off the bench. This is an awkward position, with the benches my club has attached to the shooting benches.
I was disappointed to learn thet 5, 10, or 20 rnd mags are much more expensive than the 30 rnd. mags.