So, there I was. I was planning on just blasting off some ammo. A single mag of 9mm through my Bushmaster Carbon 15. Some Winchester 115 FMJ and some Atlanta Arms 147 JHP. After I finished shooting I started picking up the brass. That's when I started noticing that there was a lot of split cases. 13 out of 30 split wide open. The other cases were badly bulging at the base. As I was looking at the cases I noticed something on the gun, something bad. The lower receiver had cracked from one side to the other, just behind where the grip attaches to the receiver. Tomorrow I will be calling Bushmaster. I'm thinking warranty, but somehow I bet they blame it all on me.