Right now, the groundwork has already been laid for a switch in cartridges. There have been repeated studies, trials, etc. that give policy makers the background to make a switch if the desire is there. There is also the development of newer polymer cases that appear promising and fit in with general goals of the military (greener, cheaper, lighter, unable to be reloaded, etc.) Fortunately, most of these fit within the current AR design which helps lessen transition issues and has proven remarkably flexible in being adapted to new cartridges with minimal changes in the design.
I think the big mistake was not adopting the 276 Pedersen. That was the right cartridge at the right time.
The 5.56 was a poor choice. The 223 round was not so much “designed” as it was a wildcat. The guys who came up with the round wanted a certain velocity at a certain range. I read the 1971 Guns & Ammo article
“The 223 is here to stay” by Robert Hutton. Robert Hutton was technical editor of Guns and Ammo magazine and must have been very wealthy as he owned a big piece of real estate in Topanga Canyon California. It was called Hutton’s Shooting Ranch. What the adoption of the 223 round as a service round shows is how well connected wealthy elites run the country. Hutton’s article documents how he developed the 223 round. If you have any sort of technical background, it is apparent he is an amateur and his cartridge represents what an amateur would do. He took an existing cartridge, necked it up and down, blew the shoulder out, changed shoulder angles, he had a chronograph, got the velocity he wanted at distance. The crowning achievement in the article was punching holes in the wobble pot helmet at 500 yards. That is about all the lethality testing Hutton did, punching holes in a helmet. He used the Powell Computer, a paper slide rule, to estimate pressures. He did not pressure test his cartridge. This cartridge was then adopted as the US service round.
I have no idea of his background, maybe he was the typical liberal arts major you find in the print industry, obviously he was a firearm enthusiast, and being the Technical Editor of a Gun magazine made him well connected. What an ego trip it must have been to have his cartridge adopted as the US service round. Imagine all the bragging you get to do at the dinner parties, “I developed the service round for the Army”. Unfortunately, amateurs don’t have the time, equipment, or understanding to really sweat out the tiny details. These guys did not have the analytical capability nor probably, had the comprehension to thoroughly study cartridge case design. William Davis, the Government Technical Expert at the Icord hearings, said on the History Channel that the technical data provided the Government on the 223 round
did not come with a pressure curve. These guys developed a cartridge and never thought of documenting what the pressure curve looked like. Pressure curve is absolutely critical to the timing of an automatic weapon. How long energy is available, the maximum pressure and how fast it drops off is fundamental to the design of a automatic gas mechanism.
This is from Chinn's Machine Gun series.
Hutton did not look at case hardness, taper, expansion or contraction. A professional would have looked at the expansion and contraction of the case in the chamber and adjusted case taper, thickness, and established case hardness in the sidewalls and case head. You would have to work with manufacturing to determine realistic hardness parameters throughout the case, but this is important as it affects the Young’s Modulus. As it turns out, the brass case 223 drags on extraction, there is not enough clearance between the case and chamber. Steel case is even worse. I have seen many failures to extract steel case ammunition on the firing line with AR15’s.
It turns out the 223 is fairly straight tapered. This was a fad, highly promoted by P.O Ackley, and widely copied. I am not a fan of very straight tapered cartridges. The one and only advantage of a very straight taper is maximizing the amount of powder you can get in the case. The wildcat era of the late 1940’s through the 1960’s was all about high velocity, and only high velocity. It was very one dimensional thinking, ignoring other aspects of cartridge design that are very important. One of the things you trade off for a straight case is that the cartridge does not “steer” well during feeding. Anyone can test this, which shape feeds better into the end of the tube, a taper, or a straight cylinder? Alignment to bore is important for feeding with all cartridges, but the really straight ones are going to jam up more often when alignment gets slightly out of whack. Straight cartridges will drag on extraction because the case walls are relaxing off the chamber walls in a straight line, not a diagonal. It turns out portions of the 223 case are still sticking to the chamber walls during extraction and a major reason for extractor lift.
Understanding Extractor Lift in the M16 Family of Weapons www.dtic.mil/ndia/2003/smallarms/din.ppt This is very undesirable as jams will get you killed in combat. Lots of good American Boys died in Vietnam with jammed M16’s in their hands. Ideally, the case will be fully relaxed off the chamber walls during unlock and there will not be any resistance between case and chamber during the residual blowback period. If you look at good case design, the Russian 7.62 X 39 and the recent Chinese service cartridge, both have more case taper than the 5.56 Nato and both were designed with steel as a case material. Both have nice thick rims, which is also important for machine gun rounds.
The Russians took into account the material characteristics of steel as a case material, examining the expansion and contraction, along with the production technology, aiding the excellent function design of SKS's and AK47's. As such, these steel rounds are outstanding in feed and extraction. The 5.56 was created without spending any time or effort on alternatives, alternate materials, anything. As such, given the fact the case shape is not optimum for brass, it most certainly is not optimal for steel.
If anything, the US should adopt the Chinese service round and probably, the Chinese service rifle. The cartridge has lots of taper, thick extractor rim, you can tell it was designed by real technical experts. The so called in house experts employed by the Army Ordnance Bureau are procurement and contract management experts. The titles of these people are Contract Specialists, sometimes Technical Contract Managers, and they are totally expert on the rules and laws of awarding contracts, managing contracts, putting money on a contract. But when it comes to actual system engineering, design and mechanics, the Bureau has to hire support contractors to tell them which end of the tube the round comes out of.
Adopting well designed Chinese weapons would reduce procurement costs and quickly put better weapons out in the hands of our troops. As an example of the well thought out nature of these Chinese rounds, the 5.8mm operates at a much lower pressure than the US service round. It only generates a 41,500 psi (284 MPa) chamber pressure which is marginally higher than that of the old single-base propellant used by the vintage 7.62x39mm and much lower than the 5.56mm M855/SS109’s 55,000 psi (380 MPa). The current pressures of the latest 5.56 rounds have been kept out of public view, but it seems to be in the range of 62,000 to 65,000 psia. Considering the proof round is 70 kpsia, the Army is operating its cartridges at pressures that are guaranteed to crack bolt lugs very quickly. You see, the AR15 was designed for a 50 kpsia round, not a 65 kpsia round. Lower pressures means fewer failures to extract when the weapon gets hot, or the Trooper is in a hot environment. It is always true that doing the job at lower pressures is better than doing the job at higher pressures.