Have you ever attempted to troubleshoot it? Unless something is terribly wrong (with the lower), I am pretty sure that you have a defective hammer spring, the trigger pin is jacked or you have something incorrectly installed.
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The 'List' has become a marketing tool for some lower tier mfrs, and some mfrs are using it to actually upgrade their products or at least offer something close to 'List' specs. And that's great. I am glad they are putting some effort into making a better product. At Delton you can now by a carbine with MPI inspected bolt, M4 ramps, etc. etc. and even get one with an FN 1-7 barrel for close to a grand. But a Colt 6920 with Magpul furniture can be had for $1059. No brainer.
A little rough on the DMPS....
My son uses a DPMS 11.5" as his go to gun. CQB, long distance, everything in between. According to him, it rocks. The damn thing takes a beating and keeps going (although in full disclosure the sling is from an old Colt 6920 kit).
http://i1284.photobucket.com/albums/...ps5bd626ac.jpg