Got it. Your are talking about our heavy barreled M16s. We originally designed two flat top M16s and equipped them with ELCAN and TRIGICON sights. I wrote the original Operational Requirements Document for both the rifle and sight. Our original 106 test bed rifles showed up in FAST Cos and were used in Somalia for Embassy defense with good effect. The original concept for a Designated Marksman Rifle was to provide a semi-automatic capability to the Scout Sniper Team. The concept eventually morphed into the 5.56mm DMR being installed in the infantry Squad. This permits precise covering fire for entry teams while allowing the SAW to be brought up to the point of attack. The original desire of the “belly shooters” was to rebuild M14s as the support rifle for the Scout Sniper Team. This was merely a smoke screen to build an empire at Weapons Training Battalion. Eventually, Wpns Trng Bn could not produce the rifle with any quality and no snipers actually wanted to carry a 14lb rifle. Once that failure was past we were able to procure the SR-25 as a hot need and have never looked back. SR-25 has a problem with breaking extractors. Both Marine and SOCOM snipers carry two extractors with them on all missions. Reed Knight has to my knowledge never been able to build the SR-25 without this problem. To achieve 1.5 MOA in a semi rifle, the tolerances between bolt head and chamber have to be tight. This tightness is thought to be the cause of breaking extractors.
In my personal builds, I put together a Remington 700, 28” barrel, muzzle brake and a tunable vibration dampener (nylon plug on a screw) in the fore stock. With custom loads, I was able to tune it down to less than .1 MOA. At that point, I was sure I was running into limitations of the bench rest I was firing from.
That was a nice rig. The main draw back was the weight as it was barrel heavy. The other draw back was that you could no longer blame the rifle.
I’m considering an M1A for my next build. Going to try it with a BOSS muzzle break and then package in a bull pup.