I recently purchased a Umarex 40 XP 20 round bb gun full blow back and locking slide after all the bb's are expended. After about a few weeks of shooting the slide stopped locking back after firing all the bb's. This was one of the features I liked for buying the gun. I called Pyramid and they said to send it back which I did and they sent me a replacement with no hassle. The new one after a few days of shooting did the same thing the slide wont lock back when the magazine is empty. The guns blowback works and the gun fires ok but I'm Disappointed about the slide not locking on empty. I think it has something to do with the magazines. I'm not sending this back but I'm wondering if anybody else has this gun and has it done the same thing. I dont know if theres anything I can do to correct it or if its just a common defect. I would appreciate any information on this subject. Other gun sites I've been on have com e up zero.