I attended a Combat Handgun class today. I just purchased the Glock 39 from the instructor who is a friend of mine. In fact it is still within the CA 10 day DROS period. But he brought it out so I could use it for the class. I was shooting brand new just purchased yesterday WWB ammo. 33 perfect rounds and I am loveing it. Now mind you there are 12 other shooters shooting at the same time. 34th round, a distinctly lighter sounding and recoiling round. I am still getting familar with the gun and think hmmmmm to myself. Pull trigger on number 35 nothing....I rack slide and spent case ejects. I think that is weird...first time I have seen that and I have been shooting Glocks for a while now. Again there is comotion all over from the other class particpants shooting away. I shrug it off and pull the trigger on number 35 again. KaBOOOM!!! MUCH LOUDER noise and a snap back and to the right recoil that is way different than I have ever experienced before. I knew something major just happened. I look down and the slide is locked back. Not out of the ordinary because it happened to be the last round in the mag. But I inspect the gun closer. The slide will not budge at all. It is seized up big time. So I call over the instructor. He checks it out. We step away from the firingline. I explain what happened. Luckily I had my CCW G26 on my hip so at least I could continue the class. He took my Glock 39 back to his table and worked on it. Managed to unsieze it and get it field stripped. Craziest thing I have ever seen. The barrel was bulged out like a snake that had just ate a big ole rat!!! Just in front of the breech. What happened...well I guess one in a million...the 34th round from what we can figure had only primer in it. A factory loaded brand new GAP cartridge with NO gunpowder in it!!!!! The bullet from round 34 traved less than 1/2 an inch down the barrel. That is why the empty case was still in the breech. When I racked it out, it loaded a brand new cartridge and I shot the bullet from shot 35 into the back of the 34th bullet stuck in the barrel!!!! No I do not have pictures today. As I said the gun was still within the 10 day wait period. My instructor has it. I hope to get some picture shortly though. He said in his 30 years of teaching classes almost on a daily basis. With millions of rounds down range he has never seen this with factory loaded ammunition. He is so amazed he wants to keep the barrel of the gun. So we are working something out. What do you all think? I have the receipt from the ammo I purchased yesterday. Who should I call first? Who in this cases is responsible or will step up? This IMO is 100% ammo related and is not Glocks fault at all. If it wasn't for the fact I was in the middle of a combat class I might have caught on to what was actually happening before I shot number 35. But I just handled it like any other malfunction. Hard to do deductive thinking in a combat class.