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Joined: Nov 2015
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Hal Offline OP
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Sidelock

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I read about the historic patent battle over rimfires.
Could someone describe how these hollow rims are formed? Just trying to get a mental image of the process. Also interested in how the priming composition was inserted.

Hal

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USAF RET 1971-95 [Linked Image from jpgbox.com]
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Thanks for sharing, skeettx!! That was great!!

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Hal Offline OP
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Sidelock

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I want to know how the hollow rim is formed. I can't envision it. How do they create the hollow with a punch?

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Sidelock
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You start with a thin brass disc about the size of a dime.

First you use a punch to drive it through a die, ending up with a long cup the size of a .22 case but a bit longer and with no rim.

The next is to drive that through a hole to meet a flat surface. There is clearance above the flat surface in which the excess brass folds sideways to form the hollow rim.

I think the trade term may be “forming a bunt” but I stand open to correction.

The rimmed case is then driven out downwards to be fed to the next stage of the process.

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Hal Offline OP
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thanks I am slowly getting it. Guess this means the thinnest metal in a rimfire case is at the edge of the rim...exactly what is needed.
Then to somehow spin primver comp into that area of the case.


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