Here’s my ideal AR system, which I would use to standardize the system:
Upper receiver:
– LMT slick MRP upper in CQB and Rifle length
– ADCOR BEAR-style forward charging handle
– KAC E3 bolt
– internal rails like on the Colt 6940P to accommodate piston-mods
– Barrel lengths from 9" (like for 300BLK and 5.45) to 18"
Lower receiver:
– Shorter and wider magwell to accommodate the wider 5.45, 6.8, and 7.62 caliber magazines
– Magwell blocks to ensure proper fit of the various magazines
– Full-ambi controls like on the AXTS and LWRC lowers
– VLTOR A5 receiver extension
Of course, most of this is already accomplished on the Colt CM901.
There ain’t no free lunch. The Masada had a charging handle further rearward and operating it was obstructed by optics. So the ACR moved it forward, and not it obstructs certain rail-mounted devices.
I have no major objections to the location of the AR charging handle, and I think that the location is part of it’s attraction as it leaves all of the rest of the gun free to mount accessories as well as place one’s hand.
I have a SR-15 upper, and a upper I built it is a 14.5" chf lw DD barrel with a carbine gas system, and the LMT enhanced BCG.
Shooting both uppers on the same lower with a Vltor A5 and using the same M885 clone ammo, They both shoot as soft as each other, with maybe a slight nod in softness to the LMT/DD set up.
I personally think the 14.5" carbine gas system, and LMT enhanced group is awesome. It has been totally flawless for me, and a real pleasure to shoot.
I think the platform could benefit greatly from a reduced cyclic rate & an adjustable gas system to allow for suppressed use, a wider range of ammunition and it might be able to mitigate gas port erosion and gas block placement to some degree as well. It seems that most of the function issues attributed to the M4 platform stem from the high cyclic rate caused by the guns being arguably “overgassed” even with TDP sized gas ports. Also from my home brew analysis there’s some design issues with the standard bolt evidenced by the fact that it tends to fail in 1 of two modes: sheared bolt lugs opposite the extractor. Personally, I like Armalite’s approach to the bolt lug issue. By relieving the offending lug it distributes the load more evenly among the other 6 lugs instead of the 1 taking the brunt of the impact. KAC’s solution was to effectively strengthen all of the lugs, but it requires a new barrel extension. Perhaps use a lubricious plating or surface treatment (NiB or nitrocarburization?) to help keep the gun running when it gets hot and dry. Outside of that I think everything else is just a preferential thing.