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.


from Shooting Times April 2009


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 the box of their 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 that 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.

Great info as usual!

Wouldnt it be more fair to check the SAAMI loads using SAAMI spec .223 chambers and not a 5.56 NATO chamber since every load except the mk262 is advertised as SAAMI spec? Strangely enough the buffalo bore is advertised as .223 pressured as well. Now the question is did they sacrifice accuracy to gain speed. Can't wait for your accuracy reports.

i have read a lot and have seen articles w/ nato barrels shooting 1/2 - 3/4 moa w/ 10rnds groups and the wyld chamber doing about the same.  just out of curiosity, why are there 2 standards in this day and age w/ the strength available to any gunmaker?  why doesn't everyone just adopt the 5.56 chamber as it seems to be an extremely accurate setup?  or, are there guns capable of 1/4 moa and at that level you need the a slightly tighter chamber?  one would think we are getting at theoretical limits here and that atmospheric conditions would come into play more than the chamber, but again, i can't shoot moa and don't reload, so i am just asking.



as always molon, your info/report is a pleasure to read.



lastly, would the difference between a saami spec chamber and nato chamber make up for the difference in the ammo that is listed @ XXXX from a 20" brl?

Possibly, but I doubt it.  The difference between COR-BON's claim of 2800 FPS from a 20" barrel and the actual velocity that I obtained of 2674 FPS is 126 FPS.  I don't think that you are going to see a boost of 126 FPS simply by changing to a SAAMI chamber (and staying within the SAMMI pressure limits.)   If someone wants to prove me wrong, all they'll have to do is get two identical 20" barrel blanks and have one chambered for a 223 Remington SAAMI chamber and the other chambered for a 5.56mm NATO chamber and then chronograph the COR-BON load from each barrel.  I think the overwhelming majority of the difference in velocities we are seeing is due to the extra four inches of barrel on the 24” test barrels.  

As an example, Hornady lists the velocity of their 75 grain TAP FPD as 2790 FPS (only 10 FPS different than COR-BONS's claim of 2800 FPS.)  When fired from one of my 20” Colt barrels with a NATO chamber that load had a muzzle velocity of 2688 FPS, for a difference of 102 FPS less than the claimed velocity.  When that same lot of 75 grain TAP FPD was fired from my AR-15 with a 24” Krieger barrel (with a 5.56mm Match chamber) it had a muzzle velocity of 2785 FPS, for a difference of only 5 FPS less than the claimed velocity.

OTM?  Will do.

I predict a run on Buffalo Bore ammo.

Nice writeup, thanks.

Dang, waiting on an order of Federal 77 grain SMK. Hmm.

excellent real world write up molon

i'll take the cor bon anyday

At prices tickling  $1.50/round I doubt there will be much of a "run".
At least not from me!

Did you see any signs of primers backing out on the Buffalo Bore load, given that it's so hot and the primers aren't crimped?  Were there any other pressure signs with that load?

Ammo companies have "non-canister grade" powders available to them that do some absolutely incredible things.

The fired primers were as flat as my date to the 7th grade dance, but none were blown, leaking or pierced nor where there any ejector or extractor marks on the case heads.  It's an Internet myth that crimped primers somehow magically contain higher mil-spec pressures that non-crimped primers supposedly can't.

I've used once-fired Lake City brass with non-crimped primers to load mil-spec rounds for an additional three firings in a row.  Using a Mitutoyo blade micrometer that measures to 0.00005", I measured the case head expansion of the same 10 cases after each of the three firings.  The average case head expansion after each of the three firings was only 0.0003" and there were no blown, leaking or pierced primers.

Thanks for the nice write-up..as usual.
I was surprised the most by the Cor-Bon results. You results were substantially different from their advertized claim.

So ....any accuracy surprises?

To be determined later this summer.

Molon, does the Buffalo Bore projectile have a cannelure?  Any idea how the terminal performance of the BB will compare to MK262, particularly if it lacks a cannelure?

Awesome.

Thanks for posting this. VERY informative thread.

+1! Your work and info is always very much appreciated Molon.

Wow, the BB 77gr is nasty stuff.  I hope it's as accurate as it is hot...

Molon,

FYI,
I just got back from my Memorial Day weekend at Camp Pendleton with my favorite Marines and headed directly to the stash checking out my 5 boxes of Cor-Bon for that Lapua brass.  No luck, it comes with Winchester Brass, not Lapua?  The box is marked the same as your picture.  Don’t see a lot # on the box.  

The head stamp is Winchester 223 REM.   Box is 223 REM 77gr HPBT.  Same as you photo......

i'll check my lot numbers it is marked lapua match

Apparently CorBon is using whatever brass they can lay their hands on, so the headstamp will vary from lot to lot. All mine are Lapua, but others have chimed in with different brass.

the lot# stamped on the inside of the 3 boxes i have is 20080301
definitely lapua match brass

I just checked my 20+ boxes of Cor-Bon 77-gr and 69-gr SMK I bought late last year from AmmoToGo. All boxes have the lapua brass.

Molon-
Thanks again for a great post and thorough, as usual. Let us know when you do the accuracy test on these. Wonder when you will get to try the Prvi 69-gr OTM and Cor-Bon 69-gr SMK?

Your guys lucked out, or I unlucked out.    

The stamp on the inside of the  box is 20080501.  

20 boxes........................damn i hate you
you dont reload do you..........................be glad to take that crappy lapua brass off your hands after your done shooting.

The advertised velocity of Prvi Partizan’s 69 grain OTM load is 2855 FPS.  The muzzle velocity of this load from the 20” Colt barrel was 2755 fps with a standard deviation of 14 FPS.

The 69 grain Prvi bullet is slightly longer than a 69 grain Sierra MatchKing;  0.930” versus 0.890”.










COR-BON’s website claims that the velocity of their 69 grain Sierra MatchKing load is 3000 fps from a 20" barrel.  From the 20” Colt barrel this load had a muzzle velocity of 2854 fps with a standard deviation of 25 fps.

Looks like that Privi bullet is sprouting a little hair.

Molon-
You are 'da MAN!!! Thanks for your chrono data. Keep us posted on the accuracy values of these when you have the chance to do your thing. Thanks again, great stuff!

The 77 grain SMK used in the Buffalo Bore load does not have a cannelure.  However, the cannelure on the 77 grain SMK used in MK262 is very shallow compared to a typical military cannelure.  I have not seen any terminal ballistic tests of the Buffalo Bore load.

http://www.rathcoombe.net/sci-tech/ballistics/tactical/tactical-test.html

maybe it is because i am on a lot of pain/migraine meds today, but the left side axis info doesn't make sense to me.  ~5-13" diameter cavity that is ~7-9 1/2" deep?  are there any pics of the gel?





 

I agree the y-axis scale is hard to discern, it looks like the widest cavity is a bit over 50mm ~2"

Also if you look at the testing data, the barrels used were 11.5" hence the reduced velocity and penetration. Apparently this was done to replicate impact velocities from a shot taken from 100m with a 14.5" or 200m with a 20" barrel

There was no ballistic gelatin involved in those tests.  They used "wetpacks" for the test media, which does not lend much scientific credibility to the results.

The cannelure or lack there of is not a significant factor for SMK bullet's terminal performance.  Nor is it a factor for the 75 grain Hornady OTM bullets.  If you are familiar with other 75 and 77 grain OTM tests you will be familiar with what any other loading will do at similar velocities.  MK262 and the BB will be indistiguishable.

there is an ad on ee for some corbon w/lapua brass kind of pricey.
last i paid for the same ammo was .75 per round shipped.
just bought some on ee with winhester brass for .66 shipped per round not bad
i cant reload it using new comps for that except maybe the winchester.

I chronographed the COR-BON 77 grain load from my 24" Krieger barreled AR-15.  (AR-15s can loose 20 FPS of velocity due to the gas system.)  The muzzle velocity was 2757 FPS.

I am a bit puzzled.  I've got some Black Hills "red box" here that I ordered a month or two ago (75gr not 77 MatchKing) and it's got the cannelure, sealed primer, and case mouth crimp (not positive on the primer crimp).  Have they changed things up since you ran your test?  

Two different loads.  This thread concerns the 77 grain SMK load, not the 75 grain Hornady BTHP load.  There's plenty of information on the 75 grain load in my TAP thread.

I understand they're different loads.  I was simply puzzled by the fact that the Red Box line I have appears to have the features of the 5.56 line you mention in your chart as missing in the Red Box line.  

I wonder if Buffalo Bore is using a powder available to us, and if so which one?

Excellent work!  This is why I load my own and chrono.  My pet load runs a 69 @ avg 2810 on 20" and is deadly accurate.

range reports?

thanks

humm, i have my 77 grain MK  running 2625 fps with a 14.5 incher.  I guess that yould be around 2800 fps using a 20 incher.

At $29/20, maybe not.

It comes out to almost $1,500/1000.

so, is your other name ATT and are you rolling out iPhone MMS?

No, but "The List" just keeps getting longer and longer.

On The List.