Sorry, I don't know enough about the construction of the rounds to say whether the threads were there to begin with. I suspect the projectile was fastened to the big shell base with a handy stud from something else, but cannot say for certain. Anybody else help w/ this?
OK, I'm reassessing the original joining process based on your latest pics; now I think it was originally put together with lead solder, which will adhere to brass just fine and hold until you drop it again.
Removal of epoxy and excess solder to prepare the areas for soldering again is most safely accomplished by physical means. Scrape off the offending material, as both old epoxy and solder will yield to a steel blade or a coarse Dremel wire brush. Turn the speed way down on the Dremel, as the friction of higher speeds will tend to just mush the solder around rather than removing it. An Xacto loop blade or scraper blade would be the first thing I'd try. This will definitely remove the epoxy, and only enough old solder need be removed to be physically out of the way of the desired position of the parts, clean and shiny to eliminate the corrosion's being incorporated into the new joint, and finally aesthetically pleasing--without excess solder appearing where you do not want it. This is one of those times when more is not better.
Apply paste or rosin flux to the exposed shiny sides of the joint, avoiding areas where you do not want solder. Acid flux is usually used for steel, galvanized, or stainless.
Solder is available in a range of melting temps from 180 to 840 degrees F; get one from the lower end.
Arrange your pieces in final desired position and hold them in place with a jig or heat proof positioning putty. I'd stabilize the final assembly so that one joined piece does not decide to fall off while you're working on the next.
Then re-solder keeping the heat as even as you can on the 2 parts being joined. A small oxy-acetylene torch tip set to a slightly reducing (soft) cone allows relative concentration of the heat applied to the joint area, to minimize heat damage to the rest of the piece. Work quickly; again, this minimizes peripheral heat damage--you're in and out before enough heat conducts to fry the paint. Generally, preheat the surfaces and swoop in with a dab of solder, which should melt, adhere to both sides of the joint, and fill the small volume between them without a lot sticking out from the joint when completed. It may be that enough solder will be left after cleanup for it to fuse together again with no extra solder added.
If heated too much, the flux's protective and cleaning properties will give way to oxidation and corrosion of the joint and surfaces; in this case, you'll have to start over with the cleanup and prep, and try again.
Practice this procedure on some scrap pieces of brass first until you have enough of a feel for what is going on. Be patient and methodical.
Good luck! Let us know how it goes...
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