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Thread: M855A1 Accuracy and Velocity

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    M855A1 Accuracy and Velocity

    M855A1 Accuracy and Velocity




    M855A1 ammunition is manufactured at the Lake City Army Ammunition Plant near Independence, Missouri. The lot of Lake City M855A1 ammunition that was evaluated for this article was manufactured in January of 2021. There were no malfunctions of any kind for this ammunition in any of the four barrels that were used in this evaluation.

    M855A1 is packaged in kraft boxes with 30 rounds in each box. The rounds are on stripper clips with 10 rounds per clip.





    The M855A1 cartridge has a nominal over-all length of 2.250”. This over-all length gives the A1 projectile a jump of 0.132” to the lands of a Colt 5.56mm NATO chamber.

    M855A1 is loaded in Lake City brass. The brass cases have the annealing iris still visible. The headstamp for this lot reads: ”LC - 21” along with the NATO cross. The case-head stamp exhibits the octal station identifiers used on Lake City SCAMP machinery. The primer pocket has four “stab” crimps and a minimal amount of sealant. The case mouth has a generous amount of asphalt sealant and is crimped into a cannelure on the bullet.












    Lake City M855A1 ammunition is charged with the St. Marks Powder SMP-842, which is a flattened ball powder. Sampled powder charges had an average weight of 26.4 grains.





    The M855A1 bullet is considered a 62 grain round, however, sampled bullets had an average weight of 62.6 grains. The M855A1 projectile is constructed from three different components; a solid copper core, an exposed steel penetrator and a reverse-drawn copper jacket that holds the other two components together. Since this bullet does not have a lead core, the only thing that fragments upon terminal impact is the copper jacket.

    It has been reported that with early lots of M855A1, it was possible to “spin” the steel penetrator inside the copper jacket with your fingers. This did not occur with any of the current rounds that I sampled.





    The M855A1 projectile has a lower specific gravity than conventional lead-core, copper jacketed bullets and is significantly longer than the legacy M855 projectile. The A1 projectiles that I sampled had a nominal length of 1.00”.

    According to Ballistic Performance of Rifle Bullets by Bryan Litz the average G1 ballistic coefficient of M855A1 is 0.291 and the average G7 ballistic coefficient is 0.149. The same reference states that M855A1 has a nominal gyroscopic stability factor of 1.41 when fired from a barrel with a 1:8" twist and 1.85 when fired from a barrel with a 1:7" twist.















    Velocity



    I chronographed the Lake City M855A1 ammunition from a semi-automatic AR-15 with a chrome-lined, NATO chambered, 20” Colt A4 barrel with a 1:7” twist.




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

    The velocities stated below are the muzzle velocities as calculated from the instrumental velocities using Oehler’s Ballistic Explorer software program. The strings 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: 76 degrees F
    Humidity: 47%
    Barometric pressure: 30.09 inches of Hg
    Elevation: 950 feet above sea level


    The muzzle velocity for the 10-shot string of the Lake City M855A1 ammunition fired from the 20” Colt barrel was 3131 FPS with a standard deviation of 18 FPS and a coefficient of variation of 0.59%.


    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, 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%.





    I also chronographed the Lake City M855A1 ammunition from three different 14.5” barrels in the same manner as described above for the 20” Colt barrel. Chronographing of the 14.5” barrels was conducted immediately after the chronographing for the 20” barrel.


    A 10-shot string of the Lake City M855A1 fired from a 14.5” Hodge Defense barrel had a muzzle velocity of 2939 FPS with a standard deviation of 23 FPS.





    A 10-shot string of the M855A1 fired from a 14.5” Colt M4A1 SOCOM barrel had a muzzle velocity of 2949 FPS with a standard deviation of 17 FPS.





    A 10-shot string of the M855A1 fired from the Bravo Company 14.5" ELW barrel had a muzzle velocity of 2966 FPS with a standard deviation of 19 FPS.




    continued . . . .
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    The muzzle velocities for the Lake City M855A1 are summarized in the table below.





    For comparison, the next two tables show the muzzle velocities for legacy military 5.56mm ammunition that also uses 62 grain projectiles: M855 and MK318 Mod 0.









    Accuracy


    I conducted an accuracy (technically, precision) evaluation of the Lake City M855A1 ammunition 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.

    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 handguard 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 used. 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 accuracy 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 Lake City M855A1, I fired a 10-shot control group using match-grade hand-loads topped with the Sierra 77 grain MatchKing (without a cannelure). That group had an extreme spread of 0.56”.











    the control group . .




    Three 10-shot groups of the Lake City M855A1 ammunition were fired in a row with the resulting extreme spreads:

    1.78”
    2.65”
    1.78”

    for a 10-shot group average extreme spread of 2.07”. 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 0.63”.




    The smallest 10-shot group . . .





    The 30-shot composite group . . .




    M855A1 compared to other mil-spec loads . . .





    In the category of useless trivia, the M855A1 bullet cuts the cleanest holes in paper targets of any 5.56mm/223 Remington ammunition that I’ve ever tested. It’s like wad-cutters for the AR-15.









    I also fired a 10-shot group at 100 yards off of sand-bags from each of the 14.5” barrels that were used in chronographing the M855A1 ammunition.

    A 10-shot group fired from the Colt M4A1 SOCOM barrel had an extreme spread of 1.85”.






    A 10-shot group fired from the Bravo Company 14.5" ELW barrel had an extreme spread of 2.15”.





    A 10-shot group fired from the 14.5" Hodge Defense barrel had an extreme spread of 2.51".




    fired cases

    left: from a 5.56 Colt M4A1

    right: from a 223 Wylde





    Lastly, for any Internet Commandos in our viewing audience today, here’s a pic of a sub ¾ MOA group of the Lake City M855A1 ammunition fired at 100 yards. The group has an extreme spread of 0.59”.








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    Part 2

    Hand-Loaded M855A1 Accuracy



    When M855A1 was introduced, we were told by people with “inside information” that this new load produced “match-like” accuracy, yet none of these people where ever able to show statistically significant data to support this claim. The test results that I obtained with M855A1 certainly didn’t show “match-like” accuracy.

    The Crane Naval Surface Warfare Center has done extensive testing with M855A1 fired from AR-15s mounted in a heavy, sliding machine-rest test fixture. The Crane Naval Surface Warfare Center is involved in developing special munitions and weapons for our warfighters. They’re not interested in sales hype and propaganda; they’re only interested in facts. They’re not driven by profit margin; their goal is providing our Special Operating Forces with the best tools for accomplishing their missions. When it comes to evaluating the accuracy of ammunition Crane uses 10-shot groups.





    With newly barreled upper receiver groups mounted in the heavy sliding machine-rest test fixture, M855A1 was only able to produce a 10-shot group average extreme spread of 2.74” at 100 yards with an average mean radius of 0.85”. With a round count of 3,600 rounds through the barrels, M855A1 was only able to produce 10-shot groups with an average extreme spread of 3.84” at 100 yards with an average mean radius of 1.10”.

    The Lothar Walther barrel that I used to test the M855A1 for this evaluation had approximately 3,350 rounds through it at the beginning of my M855A1 testing and as we saw it produced an average 10-shot group extreme spread of 2.07” at 100 yards. A 30-shot composite group of the M855A1 from the Lothar Walther barreled AR-15 had a mean radius of 0.63”.

    People are often quick to point out that the lack-luster accuracy of legacy M855 manufactured at Lake City is due among other things to the fact that M855 is composed of three different components; the lead core, the steel penetrator and the copper jacket, yet people seem to gloss over the fact that M855A1 is also composed of three different components; the copper core, the exposed steel penetrator and the copper jacket.





    We know that the M855A1 that the US Army based their accuracy claims on was not manufactured on the SCAMP machinery at Lake City, but rather the slower BAM machinery. The speed of the SCAMP machinery is significantly faster than the older BAM machinery.

    The M855A1 that I evaluated was produced on the SCAMP machinery. These M855A1projectiles themselves showed quite a bit of variation. As an example, the base to ogive measurements were all over the map.

    The picture below shows two M855A1 bullets that I pulled from the lot of ammunition that I tested. The bullet on the left shows a properly shaped base. Notice the beveled heel and the flat base. The bullet on the right has a “ridge” running around the bottom of the bullet and the base is recessed. Apparently, the speed of the SCAMP machinery comes at a cost.





    The US mil-spec for the accuracy/precision of the M4 carbine firing legacy M855 from a machine rest allows for an extreme spread of 5.0” for a 10-shot group at 100 yards.




    The US mil-spec for the accuracy/precision of the M4 carbine firing M855A1 from a machine rest allows for an extreme spread of 5.6” for a 10-shot group at 100 yards.



    It seems rather odd that the M4 carbine needs to have a larger extreme spread to meet the mil-spec when firing the load that supposedly has “match-like” accuracy. Most of my accuracy evaluation data for Colt M4 carbines was lost in a tragic boating accident, but I was able to obtain a 1.24 MOA 10-shot group from a Colt M4 barrel using true match-grade hand-loads (albeit, this group was only fired from 50 yards).



    Unlike caliber .30 and caliber 7.62mm ammunition, there has never been a National Match accuracy standard for caliber 5.56mm/.223 Remington ammunition. In 1965, the caliber 7.62mm Match ammunition was standardized as M118. The 1965 lot of 7.62mm M118 National Match ammunition had an acceptance testing mean radius of 1.9” for 10-shot groups fired at 600 yards. At that time, this was the smallest acceptance mean radius ever achieved for National Match ammunition since records were kept, starting in the year 1919. Naturally, the ammunition was tested from machine-rested, bolt-actioned, heavy test barrels.



    The composite target pictured below shows the twenty-seven, 10-shot acceptance groups (that’s 270 rounds!) of the 1965, M118 National Match ammunition fired from the test barrels at 600 yards. The small circle has a diameter of 6” and the large circle has a diameter of 12”.




    From American Rifleman, September 1965






    From American Rifleman, August 1962.



    Everything else being equal, a mean radius of 1.9” at 600 yards would have a mathematical equivalent of 0.32” at 100 yards. Now, 100 yards is not 600 yards, but then, a semi-automatic AR-15 is not a machine-rested, bolt-actioned, heavy test barrel either, so I like to use the mean radius of 0.32” for three 10-shot groups fired in a row (30-shot composite group) at 100 yards as the threshold for match-grade ammunition in 5.56mm/223 Remington when fired from a semi-automatic AR-15. A mean radius of 0.32” at 100 yards is equivalent to an average extreme spread of 1.025” for 10-shot groups.

    The first step that I took in developing a hand-load using M855A1 bullets was to cull the projectiles with the “ridged” bases.




    Next, the bullets were sorted by weight. A group of the bullets within the mean weight were further sorted by their base to ogive measurements and the bullets within this mean measurement were used for the hand-loads.

    The cases used for these hand-loads were virgin Lake City cases that were weight sorted. The necks of these cases were then chamfered, deburred and neck sized using a bushing neck die. The primer pockets and flash holes were uniformed. Priming was conducted using a Sinclair hand priming tool.

    The cases were charged with powder using an RCBS Match Master powder dispenser and the bullets were seated on a single stage Forster press. 10 rounds of each increment of powder charge weights were used to develop a load at 223 Remington velocities. Most 5.56 loads can be hand-loaded to shoot more accurately/precisely when down-loaded to 223 Remington velocities.




    The hand-loads were fired from my bench-rest set-up using the same Lothar Walther barreled precision AR-15 used to test the factory loaded M855A1 and all my usual procedures were followed. The smallest 10-shot group produced in this test had an extreme spread of 1.14” and a mean radius of 0.427” (and a score of 100-10X). Not quite match-grade, but close enough to call it “match-like” I guess.




    …..
    Last edited by Molon; 03-29-24 at 20:42.
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    I've still never seen this ammo in person. The hand loading notion is interesting. I'd be reluctant to fire the factory stuff in my guns very much because of the reported pressure levels.
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    855A1 is GTG to BC steel at 600 with a well used M4 and the Sig 6T DVO. Flatter than regular 855, difference of about a mil IIRC. That's nothing to scoff at.
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    Quote Originally Posted by ST911 View Post
    Flatter than regular 855, difference of about a mil IIRC. That's nothing to scoff at.
    Isn't regular 855 a pretty low bar?

    And isn't this stuff s'posed to be crazy expensive? For those of us in the civilian world, why would I want 855A1 when I could buy match ammo loaded with 69gr or 77gr SMKs?

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    Quote Originally Posted by Bimmer View Post
    Isn't regular 855 a pretty low bar? And isn't this stuff s'posed to be crazy expensive? For those of us in the civilian world, why would I want 855A1 when I could buy match ammo loaded with 69gr or 77gr SMKs?
    855A1 isn't available through normal commercial channels, and is expensive for its rarity where lawfully available. 855/855A1 wouldn't be weighed against an OTM/SMK - different purposes. If chosen, it would be for barrier/contingency use. There are better and more sustainable rounds for regular defensive use.

    -A1 discussion is interesting academically and tech-wise, and good info for the warfighter that has or will get it.
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    Quote Originally Posted by ST911 View Post
    855A1 is GTG to BC steel at 600 with a well used M4 and the Sig 6T DVO. Flatter than regular 855, difference of about a mil IIRC. That's nothing to scoff at.
    Wow. Shaving about a mil at 600 is noteworthy.
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  10. #10
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    Ouch. My general rule is that nothing that can be fired from 5.56 is worth $1.00 per round. 88 gr ELDMs might be worth a buck per round for shooting the mile, but that's it.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

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