I remember that Crane study. I always had a few questions about it and how it would translate into our world. They were using M855A1 ammunition, which is loaded not too far below proof pressures, not typical 5.56 NATO spec. I have to wonder how the test would've turned out if they were using M855 Green Tip. Moreover, in the civilian world where we have a lot of .223 (I've had good luck with PMC Bronze 55gr brass case and even KAC has said they use it as test fire ammo), I wonder if such a beast would be undergassed, particularly in less-than-ideal conditions, especially cold weather.
I'm aware of the URGI as referenced in the Crane study, but what other different ARs are used?Part of the "problem" with 2022 is the multitude of different AR15s used by the various government entities
What institutional users are using DD, LWRC, and BCM? I'm aware off DD and Geissele rails being used, but not complete rifles or uppers. I'm kind of out of the loop on what's in use by the "high speed low drag" guys in terms of manufacturer of rifles/uppers.Colt, Geissele, Daniel Defense, LWRC, BCM, and HK are all in large scale use by institutional users in various configurations
I've also heard here and there about LMT being in use? I know commercial LMTs use semi auto carriers and carbine buffers, but if that's what they intended for them to run with and they're reliable, I guess that's not a big deal. I seem to remember long ago, I think around 2009, there was a big hubub about LMT using MIM carrier keys, but that may not be the case now.
ETA: I really like the Colt 6920 SOCOM available now, with the 14.5" pinned/welded and SOCOM profile barrel, however I'm not sure if today's 6920s are as good as my 2009 "RESTRICTED" marked one with all the military inspection markings and such.
As far as midlength vs carbine length, as long as carbine length is reliable including under hard use, I'm good with that. I've often wondered if midlength isn't as tolerant of lower pressured .223 (though I draw the line at steel case, I'm talking good quality .223 pressure loads)
I also am still kind of partial to the quad rail and I do like the DD M4A1's quad rail and 14.5" pinned/welded barrel.