Do you have a Dremel tool handy? I have salvaged some broken scope mount screws on some pretty expensive rifles by using a Dremel and a tiny diamond-coated abrasive bit to core out the screw without damaging the threads, then using a tap to chase the threads. Some of the diamond dust bits are as small as 1/16", and with a set of magnifying goggles, it's possible to be very precise with the core-drilling of the broken screw, particularly when the pilot hole is a little off center. Check Ebay for the diamond Dremel bits. They're pretty inexpensive.

The drum is probably cast iron, so don't worry about annealing it.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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