Long Range 30 caliber AMU cartridges from 1960.

[RCS]

During the late 1950's, the US Army Marksmanship Training Unit at Ft Benning, tested some high capacity, long range cartridges. These included the wildcat Ackley Imp 300 magnum,
and a close variation was selected. Early cases made by Remington had the H&H MAG deleted on the headstamp while Winchester used the WCC 60 headstamp. I believe Winchester
Model 70 rifles were used. Some loads used 197 gr bullets while other used 200 gr bullets. These cartridges were tested for a period but dropped for the 30-338 case

[Phil McGrath]

I'm not really a big ammo collector, but those are cool.