Modern Historical Intermediate Calibers 010: The 6mm SAW

    On the right are the two major iterations of the 6mm SAW, the 45mm steel cased version, and the 50mm aluminum cased version. In the middle is a modified .25 Winchester experimental round used for ballistic testing in the early part of the SAW program. On the far left is 5.56mm M855, which became the eventual chambering for the resulting M249 SAW.

    In this installment, we’ll be looking at a very unique round. The 6mm SAW was probably the first small arms round ever designed using computer-calculated parametric analysis, and it was also probably the first American rifle round designed from the outset for steel cartridge cases. The initial design parameters were for a round effective to 1,000 meters, and which accepted a tracer that would give a visible daylight burn out to 800 meters, and this resulted in a caliber of 6mm with a 105 grain slender steel-jacketed lead-cored bullet possessing a high length/drag ratio. Although fired at modest velocity, the sleek bullet retained its energy extremely well, giving the round good long-range penetrating power, especially compared to the 5.56mm rounds at the time. Ultimately, the 6mm SAW succeeded in its ballistic goals, but was rejected on logistical grounds, as the idea of fielding three different rounds (5.56mm, 6mm, and 7.62mm) was not considered feasible.

    On to the ballistics:

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    The 6mm SAW produced two major variations: A version with a 45mm long steel case, and another with a 50mm long aluminum case. Weights of these rounds were 15 grams for the former, and 11.6 grams for the latter.

    Note: All ballistic calculations are done with JBM’s Trajectory calculator, using the ballistic coefficient appropriate to the projectile being modeled, and assuming an AR-15 as a firing platform. Also, keep in mind that there is no single true velocity for a given round; velocity can vary due to a large number of factors, including ambient temperature and chamber dimensions. Instead, I try to use nominal velocity figures that are representative of the capability of the round in question.

    EDIT: Since I’ve decided to expand this series to calibers that – while they may still be ballistically relevant – are no longer actually being produced or tested, I have decided to re-name this post (and several subsequent ones) to “Historical Intermediate Calibers”. However, I will retain the same numerical sequence and the word “Modern” struck through. Enjoy!

    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]