5.56x45 Short Range M862

This 5.56 has a small bright blue round nose bullet. Headstamp on a brass case is FC at 12, S at 3 and 88 at 6.
I assume it was made by Federal Cartridge Co., but what does the “S” mean and exactly what type of load is it?

According to Dave Hughes’ book, this is a short range load and the “S” stands for “Short Range”. Does this cartridge have a rebated rim?


Ditto on the “Short Range Training Ammunition” (current designation is M862); these rounds are meant for use in both the M16 series and the M249 LMG, but require a conversion unit (a straight blowback bolt) to work properly in either.

AKMS–Yes, the rim is rebated. Head just above the extracter groove is 0.370; Rim is 0.357. I had not noticed the rebate. Is this significant?

The bolt heads on the blowback training bolts they use for this ammo have reduced diameters, so if you were to try to fire STANDARD ammunition with them (a VERY bad idea), the firing-pin wouldn’t reach the primer. A substitution the OTHER way (SRTA ammo with a standard bolt) produces a bad jam, but not a hazardous situation.

As I recall, the bolt/carrier unit are aluminum. The light weight being needed to function with the low power short range cartridges. I think it is called the “M-2”.