BIG Freakin’ Cartridge Test 001: IMI 77gr Razor Core 5.56x45mm, 14.5″ Barrel, and Accuracy

    The first round up for the Big Freakin’ Cartridge Test is IMI’s take on the Black Hill’s classic heavy precision load, Mk. 262. Branded as “77gr Razor Core”, IMI’s version sports annealed 5.56mm NATO cases, neck and primer sealant, and of course 77gr Open Tip Match projectiles. Based on reputation alone, I expected the best accuracy and relatively high muzzle velocities from this ammunition. The test procedure was as follows:

    1. Condition ammunition to 70 °F +/- 5 degrees for at least 1 hr (in practice ammunition was always conditioned overnight).
    2. Mount chronograph to barrel or rail.
    3. Record the temperature in the conditioned container before each string.
    4. Withdraw one round of ammunition from cooler.
    5. Load and immediately fire the round.
    6. Cool chamber back to ambient conditions for 30 seconds
    7. Repeat steps 3 through 6 nine more times.

    This procedure was followed for 14.5″, 16.1″, and 20″ barrel length velocity tests. To measure velocity, a Magnetospeed V3 chronograph was used attached to the barrels of the 16.1″ and 20″ uppers, and the rail of the 14.5″ upper. In addition, three 10 shot groups were shot for each round through my Criterion 14.5″ chrome-lined 1:8 twist hybrid contour midlength barrel in .223 Wylde, to determine accuracy. These targets were then analyzed using OnTarget analysis software.

    The chronograph results for the 14.5″ barrel are as follows (Shot #, followed by muzzle velocity in ft/s):

    1. 2,696

    2. 2,655

    3. 2,694

    4. 2,675

    5. 2,664

    6. 2,679

    7. 2,691

    8. 2,748

    9. 2,665

    10. 2,732

     

    Which gave us the following figures:

    Min: 2,655 ft/s

    Max: 2,748

    Avg: 2,689

    Standard Deviation: 29.9

    Extreme Spread (highest minus lowest): 93

    As expected, the Razor Core ammunition produced very high muzzle velocities for the bullet weight, nearly 2,700 ft/s average from a 14.5″ long tube. However the readings for extreme spread and standard deviation were not so impressive, with an ES of nearly 100 ft/s and an SD of almost 30. It is possible these figures may be the result of procedural shortcomings, such as mounting the chronograph to the rail instead of the barrel itself. It is my intent to re-test Razor Core ammunition after SHOT Show with slightly different procedures to see if it makes a difference, but for now, the figures stand as they are.

    For accuracy, the Razor Core did pretty well, though not as good as I’d hoped:

    If it seems like this ammo should have grouped a bit better to you, then you’re not alone. Part of this disappointment comes from the rigor of the test – nothing looks as good in 3 10 shot groups as it does in a handpicked 3-shot group, of course. However, I think other factors may have been at play, and those will be discussed in our wrap-up installments at the end of the series.

    Nathaniel F

    Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. He can be reached via email at [email protected]


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