Hmmmm.. If only there were already a rifle round that traveled at about 1000 ft per second.. And was about 600 grains in weight.. And about .458 caliber.. And named SOCOM.. Ohhh... Wait, maybe SOCOM should look into the .458 SOCOM round.. Just an idea...
Heck, just give them a Black Powder charged Weapon, and you have what they are looking for... .50 Cal 450 Grain easily accurate out to 200 Yds, and subsonic.... the smoke from the barrel would be a Dead give-away, on Muzzle Flash, though.... Getting hit with that projectile, is like being run over by a slow Freight Train.... Massive Projectile Energy, at a slow speed. Folks have been known to jump out of the way, at 200 Yds.....
perhaps they would do well to reinvent the Ferguson rifle "Unlike the Colonists' rifles which were muzzle loaders of light .40 to .60 caliber which could be fired only about two or three times a minute, the breech-loading Ferguson could be fired as many as six to perhaps seven times in the same amount of time. It was also easier to handle because of its shorter barrel, had greater power because of its heavier .60 to .69 caliber and could be fitted with a bayonet. "