These pics, idea and parts were made by cutter. The cocking switch was made from 1/2 steel rod, and you could probably make the rings out of anything you wanted.
Instead of doing all the lathe work to the two pieces of tube and soldering them together. Just chuck up your stock in a rotary table and get the right path. Cut the deep slot, a little deeper than normal for chip clearance for the next procedure. Once you get the slot, come back with a modified end mill and cut the path for your screw heads. (I will post a picture of the modified end mill if needed.)