I’m waiting on a Yugo Underfolder scheduled to arrive next week, and in the meantime I thought I’d take the old SAR-1 out. I put 100 rounds through the SAR-1, but on the 77th round had a malfunction. This surprised me, as I’ve not previously had a malfunction with this gun. At first I thought it was a failure to feed because a live round appeared to have hit just below the chamber on the feed ramp. I popped this live round out and tried to feed another, and this one also hit below the feedramp and failed to chamber. This prompted me to take a better look, and I noticed that there was a fired casing still in the chamber. Evidently this round had failed to extract. On closer inspection, I noticed that this round had no “lip” (unsure of the proper word) around the head of the casing for the extractor to grab. At first I thought that maybe the casing was broken, but after I got my flashlight out, I could see that the casing was intact. I used the cleaning rod to knock the case out and to my surprise the head stamp read 539 and 05 (instead of Wolf 7.62x39). The casing is also slightly longer than 7.62x39, and it appears that pressure has caused the casing to expand abnormally. Here are a couple of pictures. The ammo was newly purchased as of last weekend. I purchased a 1000 round case of Wolf 122gr hp. I just opened the case, and it is the only 7.62x39 that I have, so I couldn’t have mixed it up. I loaded the magazines from the freshly opened ammo at the range. Also, I have no idea as to what caliber this round is from. I’ve never heard of 539 / 05. Anyone have any ideas? Could my gun have been damaged? What caliber was this round? I assume it must have been similar to 223, but really don’t know. Afterward, I checked the barrel which appeared fine, and fired the last 20 rounds from a Hungarian tanker magazine without any problems.