I have the flush screws that go up front on the ARMS 18. PM me your address.
It is the same thread. The one for the flash suppressor is a "dog" point, to fit the recesses of the castle nut. A cup point is better for the ARMS 18 application, but either will work if tightened properly.I'm pretty sure if memory doesn't fail me the flash suppressor set screw works , the one that holds the castle nut.