its loctited in place. Are you using a spanner wrench? If so, and it won't budge...hit it with some heat. Its supposed to be blue loctite which you should be able to get past with torque but if its red, it needs 500F to crack it (be careful not to heat the alloy lower any more than you have to). Other option is a chemical treatment to break down the loctite (same stuff used to break fixed AR gas blocks)
Posts: 1538 | Location: Leesburg VA | Registered: December 21, 2014
I never got around to removing the threaded end cap, but several members have reported using a pair of wooden dowels placed in the circular recesses, slipping a simple fabricated block over the dowels to maintain perpendicular spacing and support, and then applying a lever to the block/ dowel fixture. a la homemade spanner wrench as PGT suggests, or perhaps similar to a pair of snap ring pliers. The cap is either glued or loctited in place.