I've had real good luck with my Fulton Barrel. .5" groups at 100 yds with Federal GMM.
I started out with a DPMS AP4 I picked up for $600 - got real lucky there. Stripped it down and dumped everything but the upper, lower, charging handle, bolt & carrier. Added a stock, JP fire control, JP 15" handguard & adjustable gas block, Fulton barrel and SJC Titan comp. Sent the carrier off to Benny & he lightened it. After selling all the spare parts and the work on the carrier, I ended up with about $1000 in the gun before optics.
Here is a pic before I added the 15" handguard.