I picked up a used DPMS 20" barrel off EE. It's market DPMS .223 1-7 just ahead of the FSB on the bottom of the barrel. Can't tell how old it is. Has lugged FSB but looks like it had a perm. attached muzzle device at one point.
1) Are all DPMS .223's 1-7s really 5.56? 2) Are 1-7 barrels chrome lined? Hard to tell on this one. It needs to be cleaned up.