oubeta,
Don't take this personal or anything but I bought a DPMS pre-ban the week the ban went into effect.
I had only been out of the Marine Corps a couple of months, when I got the DPMS it just didn't FEEL like the same weapon that I had carried in the Marine Corps. Even my father who had also been in the Corps said it didn't feel like a M-16.
Went out and shot it on many occations, with different types of ammo, different mags, everything. Even had a gunsmith change all the springs, check the gas system ect. The gun would not fire, had lost faith in the AR-15 family of weapons because of this POS. Anyway I sold it and have sience bought Bushmasters, Colts, and Armalites.
I have talked to a couple of other guys that owned Pre-Ban DPMS AR-15s and everyone has had the same expierence as me. Just my .02, hope you get things worked out.