The neck portion of the just-fired case sheared away from the case body and formed a “collar” around the next cartridge when it was chambered.
Recently, while shooting a Norinco SKS, I experienced a failure to go into battery. Upon removing the cartridge, I found the round to be “shrouded” by another brass casing (top photo, with intact case for comparison). Thinking this was a manufacturing oddity, I thought nothing of it until picking up my brass and found a short casing. It seems clear that the brass case had completely separated, leaving the fore-end to catch the next round being chambered (bottom photo). In a lifetime of shooting, I have never before seen nor heard of such an event. Perhaps you could offer an explanation as to what happened? I was shooting 7.62x39 mm, 124-grain FMJ from a reputable American manufacturer. In the 40 rounds expended, this was the only incident, and there were no other problems with it.
Ron Barnes, Pert, TX
The phenomenon that you observed is relatively rare but not unheard of.
There are several causes that could result in what you experienced or something similar. Each of these causes could potentially result in the situation with the ammunition/rifle combination individually or collectively.
Since 39 out of the 40 rounds fired without incident, it would be reasonable to believe that the ammunition by itself was not at fault. That said, where the break occurred was quite close to the transition point of where the brass is annealed at the case mouth and shoulder and the case body itself. The annealed portion of the case is intentionally made softer in order for the case to seal the chamber, containing the pressure when the rifle is fired. If the case did not expand to seal the chamber, there would have been evidence of sooting as a result of gas leaking past the neck and shoulder of the case. As evidenced by the pictures you provided, there did not appear to be any gas leakage, which leads me to believe the chamber was sealed by the case neck and shoulder when the rifle was fired.
The SKS was designed as a battle rifle. That means it must perform under all kinds of conditions with little-to-no maintenance. In order to operate in dirt, dust, moisture and the buildup of firing residue from continuous firing without cleaning, the chamber necessarily has to be cut a little on the liberal side for the gun to function in these adverse conditions. The chamber typically will not have the smooth, consistent finish of a sporting rifle—by design—to reduce steps in manufacturing and therefore reduce cost without affecting the function of the gun for its intended purpose.
Additionally, the rifle’s headspace could be on the extreme edge of serviceability, which will cause a cartridge case to stretch, crack or separate. This condition usually results in a visible ring around the cartridge case or visible deformity near the head, but can happen anywhere along the length of the case with multiple contributing factors.
Excessive carbon buildup or the introduction of foreign particulate matter such as fine sand or dirt in the chamber can change the characteristics of how the cartridge case interfaces with and seals the chamber when the round is fired. Conceivably, a grain of sand or particle of carbon could retard the extraction of the cartridge case, which could in fact pull the cartridge case in two—separating at its weakest point of resistance.
With the evidence currently available, the cause of the case separation and subsequent interruption in the cycle of operation caused by the neck and shoulder of the separated case remaining in the chamber is purely speculative on our part.
If you still have the spent brass from cartridges fired on the day of the case separation, close inspection under magnification inside and out for stretching and deformation may contribute to solving this most unusual mystery.
It could have been the mechanical condition of the rifle, a fouled chamber, perhaps a less-than-perfect cartridge case or a combination of those factors that caused the phenomenon that you experienced.
You would do well to examine brass from cartridges fired in your SKS in the future, at least periodically, to see if any of the signs mentioned above come forth to help discover the culprit.