The photos below show a box which I picked up at the range session of the NDIA forum last week. The ammunition, which I was told was made by Winchester, is clearly for the current US Army Modular Handgun System competition, also known as the XM17. This requires pistol manufacturers to supply both pistols and ammunition for testing (no calibre specified, but must include both ball and expanding). One of the MHS candidates was on the range, the M17 by FN.
Sadly, all the ammo had been fired off by the time I realised that there was anything unusual present; I probably fired some of it myself, but did not notice since the magazines were filled for us. I was told afterwards that the bullet looked odd, in that it had a shoulder immediately above the case mouth, then continued to a conventional FMJ shape of a slightly smaller diameter.
No-one seemed to know what the S in SFMJ stands for, or why the bullet is such a strange shape.
Can anyone add anything to this?