77 grain SMK chronograph data: Black Hills, CORBON, Federal, Buffalo Bore

[Molon]

As many of you may already know, the muzzle velocities that ammunition manufacturers advertise for their ammunition and the muzzle velocities that we actually obtain from our AR-15s are rarely the same. Most often the velocities from our AR-15s will be lower than that advertised by the manufacturers.

It’s usually not the case that the manufacturers are trying to deceive us. It’s just that they tend to use “test barrels” to obtain their velocity readings. These test barrels usually have minimum-spec SAAMI chambers and tend to be longer than the barrels typically found on the average AR-15. While the most commonly found AR-15 barrels tend to run between 16 and 20 inches in length, quite often the test barrels used by manufacturers have a length of 24 inches. These factors combine to give higher velocities than those from a typical AR-15. The barreled actions shown below are some of the test barrels used at Sierra’s test facility.




For this chronograph session I examined five different loads, from four different manufacturers, that are all topped with the Sierra 77 grain MatchKing. Chronographing was conducted using an Oehler 35-P chronograph with “proof screen” technology. All velocities listed are muzzle velocities as calculated from the instrumental velocities using Oehler’s Ballistic Explorer software program. All strings of fire consisted of 10 rounds each.








Atmospheric conditions were recorded on a Kestrel 4000 Pocket Weather Tracker.


Temperature: 78 degrees F
Humidity: 31%
Barometric pressure: 30.08 inHg
Elevation: 950 feet above sea level






The test vehicle for this chronograph session was a Colt AR-15 with a 20” chrome lined, NATO chambered barrel with a 1:7” twist.





Prior to firing the factory loads, I fired a 10-shot string of a control load consisting of one of my hand-loads that is topped with the 77 grain Nosler Cutom Competition bullet. This load was previously worked-up in a different 20” Colt barrel to have a nominal velocity of 2800 FPS. The muzzle velocity through this test vehicle barrel was 2803 FPS with a standard deviation of 12 FPS.






The first factory load evaluated was Black Hills’ MK262 seconds. This load had a muzzle velocity of 2796 FPS with a standard deviation of 13 FPS.






Next up was Black Hills’ 77 grain “red box” load. Black Hills states on their website that this load has a velocity of 2750 FPS, but they do not state an associated barrel length with that. From the 20” Colt barrel this load had a muzzle velocity of 2687 FPS with a standard deviation of 16 FPS.






Third on the list was the new COR-BON 77 grain load. COR-BON’s website advertises that this load has a velocity of 2800 FPS from a 20” barrel. I’m here to say “it just ain’t so.” From the 20” Colt barrel it did have a respectable muzzle velocity of 2674 FPS with a standard deviation of 19 FPS. As a big plus, this ammunition comes loaded in Lapua Match brass. You’ll be hard pressed to find a finer brass case to use in hand-loading for the AR-15.






Federal was one of the first manufacturers to offer a factory load using the 77 grain Sierra MatchKing. The information printed on their box of 77 grain Gold Medal ammunition lists this load as having a velocity of 2750 FPS, but unfortunately it doesn’t list the barrel length either. From the 20” Colt barrel this lot of the Federal load had a muzzle velocity of 2550 FPS. I’ve chronogpraphed an additional six lots of this load over the last several years and the muzzle velocities have ranged from a low of 2522 FPS to a high of 2632 FPS.












Last up, but most definitely not the least is the new 77 grain load from Buffalo Bore. This load is advertised as having a velocity of 2850 FPS from a 20” barrel. I’m here to tell you this load is smokin’! From my 20” Colt barrel it had a muzzle velocity of TWO THOUSAND EIGHT HUNDRED FIFTY-THREE FPS! This is the hottest 77 grain factory load that I’ve ever chronographed. The standard deviation was 20 FPS.







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