The most likely cause of your troubles is excessive case to chamber friction. The 5.56 round is marginal with brass cases, positively problematic with steel cases.
The 223 round was not so much “designed” as it was a wildcat. The guy 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. 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, (222 Remington) 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 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 he did not have a pressure curve. This cartridge was then adopted as the US service round.
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 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.
Hutton did not examine 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.
The Russians took into account the material characteristics of steel as a case material, examined the expansion and contraction, along with the production technology, aiding the excellent function design of SKS's and AK47's. As such, the 7.62 X39 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.
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.
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.
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the easiest ersatz solution is as
@MEHavey has stated: lubricate your cases. Case lubrication will break the friction between case and chamber, and that is a good thing. Don't you want your cases to feed and extract? It is too late to chamber flute your rifle barrel, such as
Xtraxn technology from LaRue Tactical
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chamber flutes break the friction between case and chamber by floating the upper 2/3's (or so) of the case off the chamber walls.
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Case lubrication is messy, but I do it all the time. A quick measure at the range is to put a drop of oil on a handful of steel case 223, roll them around in your hand, and get oil all over the cases. Messy, but it works. It does not take much lubrication to do the trick. Never tried Baby Oil, it is not meant to be a lubricant, but it ought to work, the stuff is surely oily. Greases work well, even Vasoline. I have used vasoline and hair gels. These human rated lubricants don't contain the nasty stuff that industrial lubricants do. Fingers do have the habit of getting in eyes, mouth, and anything on the hands will get into the blood stream eventually.
Case lubrication will work as long as the chamber is not too small. If the chamber was reamed with a worn out reamer, and the chamber is small, carry a cleaning rod and extract your cases the old fashioned way, from the muzzle!