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Posted: 1/15/2026 3:51:54 AM EDT
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Pretty amazing. Using Shell Shock's new stainless steel cases, he has handloaded to 100kpsi, and is getting 75gr x 3500fps/2040 ft'lbs from a 18" barrel. Rifle has survived 5000rd, using factory Colt bolt. Only issue has been accelerated wear of gas rings, and had to replace his extractor and ejector. Barrel lasted 1moa to 3800rd before accuracy started to fall off; presumably a CHF CL barrel would last a good bit longer than a match stainless barrel.  Exposing U.S. Special Forces BRUTAL New Ammo - Ultra High Pressure 5.56 Less crazy but still impressive, Federal PEAK one piece steel case, used in the 7mm Backcounty, has been tested in 5.56. 64gr @ 3162fps from a 14.5" (so probably more like 70-80kpsi load)  Federal’s Peak Alloy is changing ammo w/ 7mm BC. This case tech increases velocity w/ similar recoil Lastly there is word that SIG has shown a "5.56 Super AP" load at AUSA, 97gr Tungsten @ 3200fps from a 16" barrel. This is almost certainly a 100-120kpsi load, and reportedly requires a new high pressure upper. Rumor is SOCOM is looking into these various High Pressure options. It would dramatically improve range of AR15, and in my opinion would be an amazing LMG round (range of 7.62 with the 200rd belt of a 5.56). I think Industry needs to talk with SIG/Federal/Shell Shock about how this technology can be safely brought to the civilian market. I believe the answer is the old .223 AI chamber for High Pressure ammo: -.223 AI will not chamber in regular 5.56, preventing High Pressure ammo in regular rifle - Legacy brass 5.56 can be fired from .223 AI chamber, so existing ammo can be fired -.223 AI has more powder capacity for even more performance Basically .223 AI to 5.56 would be akin to the .357 mag to .38sp relationship  I think this could be exciting times if handled right. |
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Quoted: The steep shoulder of the AI cases would likely cause reliability issues in any autoloading firearm. With the significant increase in pressure it would be best to alter the gas system length and port size. Would be easier to just change to a different cartridge. I'm sure this "brass" is already niche enough without changing to an oddball chamber which would rule out 99% of the existing uppers, but I do agree that .224 Valkyrie, or even .222 Remington Magnum, might be a better choice than .223 Ackley Improved. Some of the issues mentioned in OP, it seems obvious that a massive increase in pressure should be accompanied by a massive restriction in the gas system, either a metered gas tube or an adjustable gas block. |
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Quoted: The steep shoulder of the AI cases would likely cause reliability issues in any autoloading firearm. Would be easier to just change to a different cartridge. AR15's have already been chambered in .223 AI, and users report no ill effects in feeding: https://forum.accurateshooter.com/threads/223ai-ar15.4059045/ "I have yet to have a single failure to feed, my bore count on the current build is 5532. The internet insists that Ackley cases don't feed from magazines, but it hasn't happened to me." https://forum.accurateshooter.com/threads/223ai-in-an-ar-platform.3882975/ "After many thousands of rounds thru an AR, using the 223AI case in competition,I would say go for it. I don't recall having one feeding problem." 5.7x28 looks to have a comparably steep shoulder to my eye, feeds well.  I think the key to these rounds taking off is the ability to fire legacy brass cased ammo, hence the AI. Which I agree will probably need a adjustable gas system and other enhancements. If you cant use cheap, common ammo out of the weapon then a high pressure round will do no better than all the other weird niche cartridges that have been tried from the AR15. |
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Quoted: Some of the issues mentioned in OP, it seems obvious that a massive increase in pressure should be accompanied by a massive restriction in the gas system, either a metered gas tube or an adjustable gas block. I think will definitley require an adjustable gas system. The SIG Spear, aka new XM7 for Army, can fire 55-60kpsi brass in addition to the 80kpsi sig hybrid case from same rifle, so proven at least that level of pressure disparity is viable. |
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Quoted: For to live how the video graphic is using 308 rounds. Nice I think the graphic is from his previous testing of Shell Shock cases in .308, showing ~+200fps at normal pressures due to the increased case capacity of the thin wall steel.  U.S. Special Forces Testing Now - Shell Shock .308 |
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Quoted: How long will barrels last? Assume CHF and chrome-lined would be required? Per the video, his match grade (I assume stainless?) barrel stayed 1mo for 3800rd followed by a drop off in accuracy. Chrome or Nitride would increase life, as would CHF or use of better barrel steels. |
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