Your rifle is set up for single shot loading of bullets such as the Hornady 75 grain AMAX, Sierra 80 grain Matchking, Berger 80 grain VLD, and a few others.  These bullets are too long for loading to magazine length in AR rifles.

The 77 grain Sierra MK and the 75 grain Hornady HPBT are intended for loading to magazine length in AR rifles.  If the throat in your rifle's chamber is sufficiently short, I suppose you could also load them out to the rifling lands, but there may not be enough bullet left in the case neck for good neck tension; I haven't tried that, so I don't know off hand.

If you have loaded a 77 grain MK so deep that the bullet ogive is inside the case neck, you're doing something wrong, the bullet isn't that short; 2.26 inches cartridge overall length is normal for this bullet.  Check the zero on your caliper to start.

Maximum magazine length is 2.27 inches in USGI magazines and most others.  But you should load to 2.26 inches maximum for good function, and some shooters load to 2.25 inches to insure their ammunition runs through the magazine.  I have one commercial magazine that will not accept a 2.26 inch long cartridge; I don't recall the make off hand, a board member gave it to me for winning a contest a couple of years back.  It's not USA brand, however.

You have a great barrel and it likely has a good chamber and crown if done at Krieger.

Shoot good bullets at magazine length and I expect you'll be happy with the results.  If you decide you want to stretch out to 600 yards and beyond, try some of the heavy long range bullets loaded out for single loading.  This is precisely how Highpower shooters shoot a match, and they would expect a barrel chambered just like yours.  Krieger supplies tons of barrels to this crowd.

Lots of bullets fly just fine without being seated into the lands.  Some fly better if they are backed out 0.030 or so.  I don't think you're going to be disappointed.  Use good cleaning practices, including keeping the carbon ring out of the chamber throat, and you're good to go.  Look at this way, you're getting the best of both worlds and have the latitude to shoot those heavy single loaded bullets if you want.

If you're expecting a 1/4 minute rifle, you have the wrong gun.


When you start shooting 77 grain MK's, approach maximum charge weights carefully as the pressures get spooky with this bullet and they come on quickly.  Be sure to use a thick primer such as Remington 7 1/2's or Federal 205M's.