Hello 2-piper,
Thanks for your reply.
Don't get me wrong, I appreciate your input. But I'm not sure if all the side-tracked back-and-forth debate between forum members on how to measure the bores, and how the gauges worked, and how to use them, really had anything to do with my post. I'm not a machinist and didn't have any of those gauges or access to them.
I simply turned a ball, kept decreasing its size and testing it in the barrels, until I felt a "slip-fit" into the bores - and then I measured it with a micrometer - hence the 0.490" measurement.
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anyway -
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Here's the results of today's shooting.
Although I never did precisely measure the chamber cast, I got some "new" 577-500 No.2 cases which seemed to match the chamber cast. I inserted the new brass in the chambers, and they easily fit - even when loaded. I loaded 3 different bullets, an fired them. (see below) After firing, I tried slippng some of the .511 dia bullets back into the fired brass, and it was a very close "slide-fit" - perfect!
I'll test some more loads with slightly more powder to increase velocity. Pressures with all 3 loads were light with easy extraction with the fingers.
I hate paper patching so I use that method only as a last resort. Based on my results below, I don't think I'll need to go there.
The gas-checked bullets were both .511" dia and the Woodleigh SP bullets were .510" dia. This rifle really likes the Woodleigh bullets. I think all went well.