I have misc DPMS parts, first is their 7.5" Kittty-Kat upper, had to send back for service because it would not cycle, warranty,,,second,I bought a 16" SS BULL from Brownell's because they (DPMS)told me it would take a couple months to get (out of stock).. Got barrel, had cut to 12", went to assemble and "BAM", the nut would snug, then pop loose, thought I broke front of receiver with out tightening yet. Go to remove nut, turn, get snug, and "BAM", unscrews normally. Did this 4 times. Did some investigation,,, was able to casually remove the index pin from the barrel extension, and seen that hole was not bored into barrel so that the pin would lock extension and barrel together. Called DPMS,,had to send back second part that didn't work within 1--1 1/2 month. Luckily they assembled the barrel/upper for free. Just the inconvienience of sending new stuff back,,,but the 12" SS BUL has shot 1.25" at 100 with 52 Hornady HP's and 748, this with cheap scope and cold in the rain.