M82 Percussion Primer

Does anybody recognize this unknown cartridge shown below? The total cartridge weight is 472gr, and when shaken I can hear a slight metal clinking from inside that sounds like a small metal disc or ball. It’s close to a 45-70 in size, but not quite as long. Also, shown next to a .357mag:

The headstamp reads: M82LS259-288-77 (I don’t know why the rim is partially flattened on two sides):

Matt, you have an M82 percussion primer used with the ignition mechanism of several artillery pieces, including 155 mm M109A1, 75-mm M107 and 8-inch M110, M110E2 & M55. Your specimen was made by the Lone Star Army Ammunition Plant, Texarkana, Texas. There are variations made all around the world.

Thanks Fede!