I see that with under pressure loads. The brass doesn't fully expand enough to obdurate. First firing you are in effect fire forming the cases so it may go away if you can minimally size the necks next loadings. Not an expert but some of the older rifles had odd sized bores so might be worth while to slug it or do a Cerrosafe chamber cas and include part of the neck. But if accuracy is OK probably not necessary.
I bought some new 32-40 Brass not that long ago so it can be available.
Really nice rifle and a cool cartridge, hope you hunt it.
"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
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