I just finished my first complete build, all the function tests checked out and I am able to cycle rounds in and out of the chamber by hand. However, when I fire the rifle it ejects the spent case but does not feed a new round in or cock the hammer. I guess it's obvious that the bolt carrier isn't going back far enough.

This project has a rifle-length gas system and a colapsable stock with a David Tubbs buffer spring.

Can someone suggest possible causes for this problem and how I might check for said causes?

Thanks!