I recently bought a DPMS LR308 with 20" barrel, cleaned oiled it up and took it to the range. It short cycled almost every shot. I took the upper off, pulled the bolt carrier out and looked at the gas tube and key. The gas tube looked to be about .25" shorter than the one in my AR15. When I got home I looked through my parts and found a old Armalite gas tube and installed it in the rifle. It looked to come back far enough into the gas key. A couple days later I went back to the range and it cycled perfectly. So even on a factory built DPMS I had to use a Armalite gas tube.
