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Discussion Starter #1
I have a #1 in 45-70 which shows about a 0.001" constriction under the barrel band. I slugged the throat area (which is very short, almost non-existant), and the groove diameter measures 0.4593".

My question is - how large can I expect the bore to enlarge, on the chamber end, by the time I get the barrel band constriction out?

I don't want a 0.461 bore when I am finished, but I plan to shoot cast bullets exclusively and I don't think the constriction is going to help things out.

Thanks.

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The Hog Whisperer (Administrator)
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In my experience you will not see a large increase in groove diameter. Give it 20 lapping rounds or so and then slug again and see what progress you have made.

Lapping will push the throat forward a bit but that's probably a good thing in your case.
 

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Discussion Starter #3
Mike,

Thanks for the info - I will go forth without further concern. The fact the throat will be longer after lapping will be a benefit, since I can hardly chamber rounds now, even when crimpped at the shortest nose length.

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