Hey, Gary,
I just finished a Berks Co. circa 1800 rifle earlier this year. As you said, Berks guns often have double studs on the patchbox catch, and I put one on mine. (Also double pins through all the ramrod pipes, another Berks County quirk.) Anyway, here are some pics of the build in progress:[
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...and a couple of the final product:
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I realize the mechanism of the catch is a little out of focus, but basically I just cut out the catch from a piece of steel, drilled two 1/16" holes in the base, put two pieces of 1/16" rod into each, soldered them and cut them off. Then I drilled corresponding 1/16" holes in the patchbox lid, put the two rods through the holes, clamped, sweat soldered, peened, and filed everything flush. Pretty straightforward, although I guess I could have gotten into trouble if I'd drilled the lid holes off kilter.
Here's a picture of an original Bonewitz for comparison:
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Good luck and enjoy!
Gregg