I was in the Desert at sun up. I had my new M 4 Colt a TA50-4 (My first BAC sight, compact amber cross hair 3X24 carry handle mount)a Tasco 10X SS on a ARMS mount, a flat top adaptor for the TA50-4 and 400+ rounds of ammo. I set up my portable bench and sandbags and put targets at 25 yards. 100 yards and 300 yards. The close targets were two inch orange dots and the 300 yard was a B27. Getting into the ammo I found that I had grabbed the wrong can what I thought was Winchester 55 grain factory SP loads turned out to be a varmint loads with 55 grain Nosler Ballistic tips. I ran 250 of these through the M4 after sight in the iron sights and the TA50-4. I checked the 300 yard target every 50 rounds. Accuracy was so so. I kept all the rounds inside the 8 ring. (That same load will shoot MOA to 350 yards with My Savage 110FP and CZ 527 Varminter with HS stock)I cleaned the rifle at that point and put the Tasco 10X SS on. It looks funny on this carbine, (I got it for a RRA 24" Varminter that is on order) but I wanted to do some accuracy testing. I shot five, five shot groups with the above named load and five, five shot groups with a 69 grain Nosler load. Accuracy...well...it sucked, about 2 1/2 MOA. I then tried some Federal 50 grain HP factory loads and got a smile on my face. The five, five shot groups averaged .9" with two groups under 1/2". I had a very hard time with the trigger. I've been shooting several CZ rifles lately with single set triggers that break at 12 oz. The Colt trigger will take some getting used to. I then moved all the targets into 25-60 yards and put B27 on them and played with the BAC. Yes I'm hooked. That is the most fun a man can have standing up. I did not try the flat top adaptor on the TA50-4 but I will. The short eye relief was a bit too short, (first time I ever indexed a cheek weld by putting a charging handle in my right nostril). The muzzle break is ugly and way to noisy. I forgot and left out my left ear plug and fire a round. Damn, I thought I'd just been bitch slapped for a second. Any way, the M 4 cycled flawlessly and shows very good accuracy potential. I think I picked a keeper.

just for reference, are your measurements center to center, or from the outsides?

Outside to outside then subtract .224.

I short changed the Colt M 4. I just ran the numbers, ( the "about 2.5 moa" above was a guess) the 55 grain Nosler load averaged 1.78" and the 69 grain Nosler J4 load ran 1.84". I don't have much to compare this to as this is my first AR15. Is this about Par for a 16" barreled M4??

Sounds a bit off to me, but it might not like that ammo.  Either way, the M4 is a CQB type weapon, not a sniper system, so I wouldn't worry too much.

I understand the CQB vs Sniper nitch. The 10X scope will not be staying on the M4. Actually I can live with being able to stay inside the 8 ring, (aprox 12" wide by 18" high)of a B27 at 300 yards with the TA50-4. However, I will use the 10X (or higher power) scope for testing ammo and load development. I believe an Aimpoint, (with BUIS) will be the long term site choice.