I got a new AK74 a friend of mine built me a few weeks ago. Took it to the range, and it wasn't ejecting right. Kept throwing brass into the internals and locking the bolt up. I talked to him and he walked me through taking apart the bolt. The bolt and the part that ejects the spent shell had a bunch of carbon buildup in it, and we figured that must have been the problem. Took it back to the range today, and again same problem. It even threw one on top of the bolt and popped the dust cover off and into my face. Scared the fuck out of me. Any ideas as to what I could try next to fix it? I plan on asking my friend for a new bolt and see if that will do it, but I don't see anything wrong visibally with this one.