My ammo finally arrived. The testing consisted of wet phone books and water in foam icechests. Whether book or water, the front half of the sost disintegrated at 50 yards from a 16" ar. It performed just like a nosler ballistic tip while the rear was like a solid copper wadcutter from the first "band" back.
http://i54.tinypic.com/2rfrmtk.jpg It was not at all yaw dependent and fragmented nearly immediately. I do not know if the front crushed and shattered, or violently over expanded. It left a lead and copper snowstorm in whatever it hit while the copper rear punched onward. It went through about 10" of soaked book and 20" of water. The fragmentation was in the first 1-6" of books. M855 I tested left a bigger hole in the soggy books, but was 100% yaw dependent. Consider the front 1/2 to be equal to a slightly sturdier speer TNT projectile and the back half a solid copper slug with a flat meplat. A real "do it all" round that frags violently and still easily penetrates 14"+.
http://i54.tinypic.com/287jbqp.jpg
(ignore the bit of jaggedness near the front band, it is where I gripped the round with pliers to cross-section it.
Compared to a .277cal 90gr Speer TNT round (sourced from the internet).
http://i56.tinypic.com/2zrgoqt.jpg
The SOST does not appear to be fluted like the TNT, but I have no way of measuring the "hardness" of its core, the ductility of the jacket, etc. All I know is that it performs IDENTICAL to a Winchester BST when fired into foam ice-chests full of water. The first ice-chest (about 10" deep) has a flurry of sand-sized lead and copper, but unlike the BST, the SOST round's "shank" continues through the first, second, and third ice-chests, and fell to the ground after bouncing off the exterior of the fourth. It also penetrated 2 ice-chests and about 10" of waterlogged (only soaked for 20 minutes) phonebooks. That little rear-half has some serious penetration, and the front half just seems to disintegrate.