Between 1957 and 1966, National Match accuracy varied between 2.0 and 3.8 inches for the smallest circle that included 50% of the holes at 600 yards.
CAUTION! The 50-grain M72 load of IMR 4895 is not a Garand load and is an error taken from bad information in the Army's TM-43-0001-27. The same technical manual lists the same 50-grain charge of IMR 4895 for the 152-grain M2 Ball bullet as it does for M72. TMs have general technical information for soldiers and are not nearly as carefully produced as actual maintenance or production procedure manuals (a process I've been through with a product I designed, and which required paying $20K to a specialized consulting firm to complete; that was the price in the late 1990s). Bottom line: the TMs can be sloppy on technical details, like failing to report whether the "psi" stated for a cartridge pressure is taken off a copper crusher or a piezoelectric transducer reading. This has caused much confusion over time, so Reader Beware.
Akinswi,
The short answer to your question, to the best of my ability to determine it, is a charge of 47.3 grains of average canister grade IMR 4895 under the 175-grain MatchKing, using Lake City brass and a #34 primer copies the old M72 load.
The actual National Match loads produced from 1957 to 1966 varied with lots of IMR 4895 from a minimum charge weight of 46.0 grains to a maximum of 48.5 grains. The average of all load values used in that date range is 47.3 grains. The 78-foot 2460 fps number comes from the 1957 post-war resumption of production of military match ammunition. It was produced by Frankford Arsenal and used 48.0 grains of IMR 4895 that achieved 2640 fps at 78 feet from the muzzle of a tight chamber spec pressure and velocity barrel with the cartridge handled to keep the powder laying back against the case flash hole at firing. Using the BRL's drag function determination for the M1 Type bullet used in National Match ammunition, the QuickTARGET Unlimited ballistics calculator shows this would have been going 2681 fps at 15 feet from the muzzle. Hold that thought.
In 1961, Frankford Arsenal apparently got a different lot of IMR 4895, as the charge in that year’s NM ammo was increased to 48.5 grains, but the 78-foot velocity is reported to be the same 2640 fps.
When Lake City took over the manufacture of M72 in 1962, the test method changed. They used a lot of 4895 closer to what Frankford Arsenal had used in the 1957-1960 NM ammo and apparently, they had a commercial-style chronograph setup for 15-foot velocity measurement, and they measured 2685 fps from a 48.1-grain charge. This is what you’d expect from shortening the mean measuring distance from 78 feet to 15 feet and adding 0.1 grains to the original FA charge of 48 grains. Based on Hodgdon’s data for IMR 4895 with a 175-grain bullet, velocity increase is 40.7 fps/grain of powder. If 48 grains produced 2681 fps at 15 feet (2640 fps at 78 feet), then 48.1 grains would produce 2685.7 fps, which is close enough to the reported 2685 fps to be well withing normal measurement error expectations. I doubt that’s a coincidence. I expect my access to a computer and the BRL drag function allow me to anticipate the velocity measuring change more accurately than they could do by hand, and that’s what accounts for the 0.7 fps discrepancy.
The old RF oscillator screen chronograph equipment used by the military and by Frankford Arsenal had a one-yard measurement starting trigger coil and a 51-yard stop coil in the standard setup (hence the 26-yard or 78-foot-from-the-muzzle mean center distance), so a more modern SAAMI-type optical unit like the Oehler commercial units with a 15-foot mean screen center would have brought about that measured velocity change.
In 1963, the powder lot changed to a faster burn rate and caused the charge to be reduced to 46.7 grains, while still producing 2695 fps at 15 feet (2653 at 78 feet). The boxes still kept the 2640 fps label. The 1964 batch produced 2669 fps (2628 fps at 78 feet) from 46.0 grains of 4895, which is a change of 37 fps from the previous year, and which is just about right for a 0.7-grain drop-in charge weight for the same lot of 4895 as was used the previous year. Why the change? I don't know but expect accuracy testing was involved.
In 1965 Lake City used 46.5 grains of 4895 to get 2705 fps (2668 at 78 feet). Clearly a hotter lot of 4895, as the same lot would be expected to produce 2689 fps for that charge change.
In 1966, 47.2 grains of 4895 produced 2711 fps (2669 fps at 78 feet). This was a slower lot of 4895, as the previous year’s lot would be expected to produce 2731 fps at this load level.
So that’s what I have of the history of this stuff. Start with the 47.3 grain load and vary it between 45.9 and 48.7 grains to cover the powder burn rate tolerance and see what works best inside that range.
