Hey,
FYI, I am new to the ammo section and I read all the FAQs and Rules for this section.  I also did a search for related topics with no luck. Anyways, I was out shooting a new Mk 12 inspired build (I am too poor for a true clone).  I used MK 262 in service and love the round and can't bring myself to go back to M855.  So, I am trying to find an affordable alternative.  I was shooting at the house and I had a significant POI shift between black Hills MK 262 and IMI 77 gr razor core.  I shot both within a time period on the same day that atmospheric conditions should not have been a factor.  I shot a group of 5-7 rounds at 300 yards of black hills and verified my POI was center/center.  I switched to IMI razor core and shot a 5-7 shot group that hit .7 mils low and center.  I let the barrel cool and flipped the order and shot the IMI first on the second round and the black hills second.  Same results.  I have made known data cards for the real MK 262 at every thing from 200 - 600 yards and figured the slight velocity difference would allow me to use the same dope for both loads( double checked this with my ballistics software).  I got the muzzle velocities from the list here on ARFCOM as I do not own a chrono (2756 for the black hills vs 2770 for the IMI based on an 18" barrel and 20 fps loss per inch from the factory tested 20" barrel ).  I am not sure what I am missing? They both use SMK 77gr HPBT with the mod 2 cannelure, similar muzzle velocities. I know that no two different factory loads are going to have identical POIs, but 7.5" low at 300 yards seems extreme.  What could it be? OAL, different powder burn rates making the IMI loose more than 20 fps per inch? I tried several different boxes of the IMI stuff with the same results.  I know I can just make known data cards for the IMI 77 gr but I am curious what could be causing this and feel its a good learning opportunity.  I feel like I am missing something obvious.  Any input would be appreciated.

I suspect it is due to velocity differences.

When I tested the BH load I got ...
..........................................................................................................16" Middie.......................20" Rifle ..................
Black Hills 77gr 5.56 OTM .........LC 14 ( NATO Cross )............Av. 2592 , ES 21................Av. 2675 , ES 82..............Very accurate
Black Hills 77gr 5.56 TMK .........WCC 14 ( NATO Cross )...........Av. 2636 , ES 54................Av. 2753 , ES 63..............Outstanding Accuracy.

IMI 77gr OTM.............................IMI 13 variety of 2 digits.........Av. 2726 , ES 39..................Av. 2810 , ES 41........... Not the most accurate, but certainly a good value.

Frankly,  .... out of all the 77gr Loads I tested.. ( Here...well worth a look IMHO IMI was faster then most all of the rest of the 77gr's and the only commonly available 75gr that beat it was the Superformance 5.56 75gr

Thanks, for the link.  Great stuff!  I believe you may be right about the velocity.  But, even with the difference between the IMI and the Black Hills, I am happy with the way the IMI shot once adjusted for elevation. I am not trying to win a benchrest competition I am looking for combat accuracy for a DMR.  And, I can afford to shoot it weekly.

Getting a chrono or borrowing one would answer the question and get your dope cards that much better.............  
In other words, I think the difference you are seeing is the actual velocities vs book ones.............

The longest range I have available to me currently is 100yds, but that said I have seen no descernible POA/POI shift between IMI 262 and BH 262. Both are capable of sub-MOA(averaging .75) 3 shot groups out of my BCM Mod 0 upper. A slight hand in repeatable groups may go to Black Hills.

Might be time to get a chrono. Never had any experience with them any recommendations?

I haven't shot groups at 100 yards to see the POI shift between the two. I think it would be interesting to see at that range if the POI change stays at .7 mils.

Also, where in SC are you? I shoot out to 500 yards at my house and have a 1,500 yard range about 20 minutes away.

IMI “Razor Core” 77 Grain OTM, LR, Mod 1







This load is topped with a 77 grain OTM bullet with a cannelure.  The case mouth is sealed and the primers are crimped and sealed.  When chronographed from the 20” Colt barrel, the load had a muzzle velocity of 2866 FPS with a standard deviation of 21 FPS.

A 10-shot group group fired off the bench from my Lothar-Walther barreled AR-15 at a distance of 100 yards had an extreme spread of 0.95”.








….

Range Report:  Black Hills MK262 Mod 1





The 77 grain MK262 ammunition produced by Black Hills Ammunition has been referred to as the most accurate mass-produced 5.56mm ammunition that has ever been type-classified and issued by the US military.  Since its inception, genuine MK262 has been manufactured solely by Black Hills Ammunition.  For years, MK262 was only available to the civilian population as “seconds,” but more recently Black Hills has made first-run production lots available on the commercial market.  It is the first-run version of MK262 Mod 1 that I tested for this report.

MK262 Mod 1 is loaded in WCC 5.56mm brass and uses a cannelured version of the 77 grain Sierra MatchKing.  The round is charged with a proprietary ball powder.  The primer pockets are crimped and sealed.  Contrary to erroneous information that has been posted on the Internet, MK262 Mod 1 does not have case-mouth sealant.















The 77 grain MK262 Mod 1 projectile compared to the M193 projectile.







MK262 powder.  (The squares of the red grid measure 1/10 of an inch.)





The specification for the accuracy/precision portion of the lot-acceptance-testing of MK262 calls for multiple 10-shot groups to be fired; which is exactly what I like to do for a range report.  An accuracy (technically, precision) evaluation of the first-run MK262 Mod 1 ammunition was performed following my usual protocol.  This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any Group Reduction Techniques (e.g. fliers, target movement, Butterfly Shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Also, a  control group was fired from the test-rifle used in the evaluation using match-grade, hand-loaded ammunition; in order to demonstrate the capability of the barrel. Pictures of shot-groups are posted for documentation.

All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrel used in the evaluation was free-floated. The free-float handguards of the rifle rested in a Sinclair Windage Benchrest, while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was attached to the objective-bell of the scope. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.









The Wind Probe.





The test vehicle for this evaluation was one of my semi-automatic precision AR-15s with a 20” stainless-steel Lothar Walther barrel.  The barrel has a 223 Wylde chamber with a 1:8” twist.








Prior to firing the MK262 ammunition, I fired a 10-shot control group using match-grade hand-loads topped with the Sierra 77 grain MatchKing.  That group had an extreme spread of 0.69”.






Three 10-shot groups of the MK262 Mod 1 were fired in a row with the resulting extreme spreads (from smallest to largest):

0.96”
1.12”
1.21”

for a 10-shot group average extreme spread of 1.10”.  The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group.  The mean radius for the 30-shot composite group was 0.33”.  




The smallest 10-shot group.






The 30-shot composite group.







I chronographed the Black Hills 5.56mm MK262 Mod 1 ammunition from a semi-automatic AR-15 with a chrome-lined, NATO chambered 20” Colt M16A2 barrel.









Chronographing was conducted using an Oehler 35-P chronograph with “proof screen” technology. The Oehler 35P chronograph is actually two chronographs in one package that takes two separate chronograph readings for each shot and then has its onboard computer analyze the data to determine if there is any statistically significant difference between the two readings.  If there is, the chronograph “flags” the shot to let you know that the data is invalid.  There was no invalid data flagged during this testing.

The velocity stated below is the muzzle velocity as calculated from the instrumental velocity using Oehler’s Ballistic Explorer software program. The string of fire consisted of 10 rounds over the chronograph.














Each round was single-loaded and cycled into the chamber from a magazine fitted with a single-load follower. The bolt locked-back after each shot allowing the chamber to cool in between each shot. This technique was used to mitigate the possible influence of “chamber-soak” on velocity data. Each new shot was fired in a consistent manner after hitting the bolt release.  Atmospheric conditions were monitored and recorded using a Kestrel 4000 Pocket Weather Tracker.









Atmospheric conditions

Temperature:  79 degrees F
Humidity:  37%
Barometric pressure:  30.12 inches of Hg
Elevation:  950 feet above sea level


The muzzle velocity for the 10-shot string of the Black Hills 5.56mm MK262 Mod 1  ammunition fired from the 20” Colt barrel was 2848 FPS with a standard deviation of 10 FPS and a coefficient of variation of 0.35%!

For those of you who might not be familiar with the coefficient of variation (CV), it is the standard deviation, divided by the mean (average) muzzle velocity and then multiplied by 100 and expressed as a percentage. It allows for the comparison of the uniformity of velocity between loads in different velocity spectrums; e.g. 77 grain loads running around 2,650 fps compared to 55 grain loads running around 3,250 fps.  

For comparison (and to give you an idea of how good the CV is for this factory loaded MK262 Mod 1 ammunition) the mil-spec for M193 allows for a coefficient of variation of approximately 1.2%, while one of my best 77 grain OTM hand-loads, with a muzzle velocity of 2639 PFS and a standard deviation of 4 FPS, has a coefficient of variation of 0.15%.









….

For starters, your "20 fps loss per inch" claim is most likely inaccurate.  I've chronographed two different 5.56mm loads back to back (using 30-shot strings of fire over an Oehler 35-P chronograph) from an 18" Noveske SPR barrel and a 20" Noveske DCM barrel, both with Noveske Match Mod 0 chambers and 1:7" twist rates.  The difference in velocities of both loads was over 100 FPS.










Secondly, even if the IMI and Black Hills loads had the same muzzle velocities, they could have been loaded in different cases, using different powder and different primers (and one load has case-mouth sealant and the other doesn't).  This can result in different recoil vectors and barrel harmonics which in turn lead to differences in the points-of-impact.


...

Thanks for the info Molon!  Did you get a cv for the IMI 77 Gr OTM?

Nevermind you gave the mean and SD.

I'm in Greer/Blue Ridge. Are you referring to SCOTG?

Yep

Play around with this App.... it is actually quite good.

http://apps.vortexoptics.com/lrbc/

Which mils?

thousandths of an inch (distance),  .0007" is nothing

artillery mils (1/6400 of a circle, angle), 7 inches at 300 yards, not good

milliradians (angle), 1.2" at 300 yards, normal change in impact when swithcing ammunition.

I don't know what you mean by which mils. You know which mils I am talking about when talking about ballistics and long range shooting.  A mil (mrad, miliradian, a measurement of angle [ All versions of the angular mil are approximately the same size as a trigonometric milliradian]) is all the same of which there are approximately 6,300 in a circle.  As far as .7 mils being 1.2" at 300 yards I do not understand your math.  Example A: Convert 1 mil to inches at any distance (3.6)(300 yards)/100= 10.8 inches and 7/10 of 10.8 = 7.56" at 300 yards Example B: Convert mils to MOA and MOA to inches (.7 mils)(3.375)= 2.36 MOA now convert MOA to inches   (2.36 MOA)(300 yards/100)(1.047) = 7.41" at 300 yards. I am not sure where your 1.2" at 300 yards came from. Please explain.

Thanks bfoosh, I will check it out.

I think he divided 3.6 by 3 instead of multiplying it by 3.

That's not gonna be good when the targets are returning fire.

This, IMO is the answer. Any time you switch ammunition you can see drastic changes in POI, even with the same projectile.

 

I use the "Alpha" Chrony..............  Works well and reasonably cheap..........
Just my humble opinion:

-Get a chrono and start with real numbers shot with your rifle.

-I shoot groups/ ammunition tests at 200yds.  Just my 2% but shooting at 50yds or even 100yds doesn't give a clear showing.
What I mean is, you are shooting out to what, 600yds?  The further out, not closer in, will show those differences much clearer.
And at say 25yds, you could probably shoot ANY ammo and it would/might hit man sized target.  But as you've noticed at say 400yds, those differences are a miss.  
   

Thanks for all of the valuable input guys.  I think a chrono is in order. This being my first foray into shooting precision in the civilian world there are a lot more choices and more choices mean more data needs to be collected.

OP-Sent you a PM. Also, might be of interest, I'm testing tomorrow some Winchester 77gr BTHP that's rated at the same velocity as Mk262. I'm curious to see the POI shift compared to IMI and BH.

Quite probable.  But, I think I just screwed up taking the sine of .07 milliradians....

Should be 6.8"

Oh, and an artillery "mil" is 1/6400 of a circle, unless you are Russian (1/6000 of a circle), or an old Swede (1/6300)

I am going off the definition of mil I was taught in the Army and am using the math I was taught in the Army. All of my math is based on 6,400 mils per circle.  There are 60 MOA per degree and 360 degrees per circle, therefore (60)(360) = 21,600 MOA per circle.  Which means there are approximately 3.375 MOA per mil.  So, if my shot was .7 mil low then (.7)(3.375) = 2.36 MOA low at 300 yards.  Then, 2.36 MOA at 300 yards is (2.36)(300/100)(1.047)= 7.41 inches at 300 yards.   I am still not understanding your math.  

I have never heard artillery mil.  But, I was never FA.