The problem with filling, drilling and tapping is going to be the screw thread. It will be some kind of metric size, and a non-standard pitch at that. It is highly advisable to measure this thread first, before you discover that the required taps are unobtainable.
I have an idea, but before going off into unworkable solutions, may I ask you to 1) measure the thread on a cleaning rod as accurately as you can, and 2) provide good front and back views of the barrel band. I'm thinking along the lines of plugging the back half of the threaded hole, keeping the front half to use as a guide...
Or, as a minimum solution from the "creative laziness" department, you could simply try wrapping a couple of turns of fine Teflon tape around the thread on the rod. That might be sufficient to hold it in place.