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Rim thickness

Posted by Ken Smith on Wednesday, 21 March 2012, at 6:38 p.m.

Ernie, Steve,& Bill, At Ernie's prompting, I just returned from the loading bench where I had been measuring rim thicknesses of Winchester cases. This is what I found. I first measured an unfired case, then 10 fired cases of unknown ages. I approached these rims at two different angles with my calipers, and now I am confused as to which is the correct. I came straight in point first and got one measurment, then from the side of the point of the calipers where I could get more of the rim in them, and got a different measurment. So with a new case straight in, point first, it measures 0.0720, and from the side of the caliper point, the measurment is 0.0665. The ten fired cases were done the same way, and they varied from 0.0655 to 0.0675 point first. From the side of the calipers, 0.0635 to 0.0655. Either way, this shows a reduction of thicknesses between new brass and fired brass. Agreed? Now here is another ringer. I found variations in thickness of a rim all around the clock, taking these measurments at roughly 90 degrees from each other. I found this on both the new case and the fired stuff. Now here is something that will blow you hat in the creek, I have an original live tinned brass rifle cartridge loaded in 5/89. The rim on this guy measures 0.0565. I am beginning to lean toward the idea of worn primer pockets for the cause of the flattened primers. Are there any machinists amongst us to tell me which was the proper way to gauge the thickness of a rim? What do you boys think? Regards, Ken


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