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. 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. According to MD Roberts the mk318 offers effective ballistic out to 100m from a 10.5" barrel (about 2350fps). 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"+.


(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).

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 feel 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.

Exactly.  What do you think would penetrate barriers better?  This or a bonded round like the fusion?

The hole it made in the books opened up without any sign of yawing. Peeling the pages apart, the hole simply grew larger and larger. With the M855, it was plainly oblong before it fragmented.

All that is left is the shank, which has already been pictured. However, I will again picture it for you:


(Not bad for my cell-phone :) )
The rest of the front of the projectile was a lead and copper snowstorm, the largest piece of which MIGHT have weighed 3-5gr. This was a result from hitting the water in the ice-chest. The phone-books caused fragmentation on a level that I never saw but a few shiny slivers of copper.

The fragmentation of the round when fired into water was fully contained in the first ice-chest (about 10") while the rear shank continued on through the next 2.

A bonded round would be superior for wood/multiple thin layers of sheet-metal/glass.
M855 is better on steel and concrete(per MD Roberts' testing). Copper sucks for penetrating hard barriers that are thick/homogeneous, like plate steel, etc.

i need to know what distance these will still fragment.

If the bullet wont fragment anymore, after that distance its no better than any of the other FMJ OTM bullets.

ETA I dont see how this bullet fragments without yaw.

It fragments without yaw the same way a Speer TNT varmint bullet fragments without yaw. The impact either radially stresses the front 1/3 of the jacket, or it "hyperexpands" and fragments. I don't know which is the actual mechanism. All I know is the results are IDENTICAL to the 55gr BST I shot into the same mediums a few years ago.

According to MD Roberts, "it seems to work adequately out of 10.5" barrels at ranges from 3m to 100m" (about 2350fps). That can be interpreted however you like.

Further...
Look at the shank.
All 360* of it show roll-over on the edges by the front band. Also, looking at it in person, it has expanded radially for the full 360* diameter, ever so slightly.

Had it tumbled to initiate fragmentation, 180* (or so) would be expanded, the other 180* would be bent inward, NOT outward, etc. etc.

Hard to express in words, but the picture should suffice.

The front 1/2 disintegrated with no tumbling evident in any way either from looking at the shank, or the target.

I can say with 100% certainty that this round did NOT tumble before it fragmented, and with relative certainty that it did not tumble afterward while moving at any significant velocity, due to the fact that the sheared area ahead of the front band is rolled backward toward the rear of the bullet for the full 360* circumference.

12GA

Can you tell me the weight of the copper base

Someone weighed one in at a bit over 30gr, and theirs sheared at the same place the 2 rounds I recovered did. I THINK I recall them claiming @32gr. I would dare wager that mine are within 2gr of the same, judging by the fact that they shear off predictably at the first band.

I plan on testing then in some wood 2x6's. I tested M855 in the same and it did not fragment until yawed 3-4 boards in as I recall. Definitely dependant on Yaw. When I shot a 2x4 with a 55gr BST, it only went through 1 and into the 2nd, ending up a snow-storm. I am thinking that this bullet will snow-storm the front 1/2 in the first and maybe second board, and then the shank will continue a little ways. Very curious. Just my prediction.

Any way you slice it, the round went through 30" of water and a bit of foam. I believe the correlation is water penetration divided by 2.5 = approximate penetration in flesh, and six 1" thick Styrofoam walls are worth a few inches in water I'm betting, so at worst, we have a round that fragments like a .22 hornet and yet still sends a good chunk of itself the requisite 12" or further.

http://bulletin.accurateshooter.com/2010/02/usmc-adopts-new-open-tip-sost-5-56-ammo/

Thanks

tag for results.

Mine looked similar after cinder block shots.

cinder blocks  How many?

are those like the concrete blocks used to build house etc? ?


I shot some concrete blocks with the 7.63 x39
Man I was amazed what that caliber can do to a few Blocks

Makes me want a 6.8

DR roberts said over on m4carbine.net that they had ordered mMK318 but he hasent tested it yet, im sure if he said that he was quoting the militarys info.

someone has to fire these at distance or out of a shorter barrel.

MD Roberts already has. They do fine at 100m from a 10.5" barrel. He posted what you are saying he posted, almost a year ago, back in 2010.

Page 23 of THIS document indicates that the round is not yaw dependent.

I cannot find my calipers and a frustrated to no end about that. However, Molon pulled one and compared it to M855 in a picture and it looked to be within .1-.15" of the same length, as best I could tell. Let me go hunt for my calipers again *sigh*