Interesting mold

I picked up a 4 cavity Saeco mold from Gary's recent estate sale that is somewhat unusual. Saeco lists it as a 140 grain 9mm mold. Bullets measure 356/357" depending on the alloy mix. It's the fourth cavity that's intriguing.

The standard cavity bullets weigh 140 grains and the larger comes out at 160 grains. Could be designed for subsonic maybe? I think it would have a hard time feeding in any 9mm auto. Powder coat and load in a 357 Magnum/Maximum?