Well, I'm glad I'm not the only who has had this happen. I was worried for a while. I seem to get a flame flash out the back of the gun under the slide as it travels rearward whenever I shoot the Remington UMC brand 9mm 115 gr. FMJ stuff that comes in those yellow boxed 250 round packs. This particular brand is very light recoiling and that fact coupled with the occasional flame out the back makes me think they are using a slow burning powder that still had some specks unburned when the barrel unlocks from the slide during recoil and the unburned specks ignite after unlocking. When this happens I check my brass and I do notice carbon fouling on one side of the casing like some of you described. I have not seen this flash of flame happen with hot loads. I fired a few mags each of the famous Federal 9BPLE 115 gr. +P+ JHP and some Buffalo Bore +P+ stuff just to make sure they functioned in the gun and they all functioned normally. I have only had the flash of flame out the rear with the Remington UMC stuff. Never had it happen with Winchester white box or Federal range, target, practice ammo or Aquila.