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Naga · July 30, 2011, 01:48 AM

Hello everyone.

I just picked up an RCBS Trim Pro. It has been modified to run off of a power drill. I will be using it in place of my Lee trimmers, since it became a bear to prep a few hundred cases by hand after every range trip.

I noticed that RCBS claims that the Trim Pro produces very square case mouths. I decided to test this with my caliper, and I was astonished to discover a nearly +/-".004 variance around the mouth of each of the test cases! The difference was discernible to the naked eye when held against a measuring square.

Either way, I tracked this problem down to poor alignment between the cutter shaft and the axis of the casings when they have been placed in the holder. Through the judicious use of bits of spring steel as shims, I attempted to correct the issue. I have gotten it to the point that the variance is +/- ".0005 (the smallest increment my caliper displays.)

My question is this: How square does a case mouth need to be for good accuracy? Would the above stated tolerance be acceptable?

Thanks for any help

July 30, 2011, 01:48 AM	#1
Naga Junior Member Join Date: July 30, 2011 Posts: 1	Question About Case Mouth Squareness... Hello everyone. I just picked up an RCBS Trim Pro. It has been modified to run off of a power drill. I will be using it in place of my Lee trimmers, since it became a bear to prep a few hundred cases by hand after every range trip. I noticed that RCBS claims that the Trim Pro produces very square case mouths. I decided to test this with my caliper, and I was astonished to discover a nearly +/-".004 variance around the mouth of each of the test cases! The difference was discernible to the naked eye when held against a measuring square. Either way, I tracked this problem down to poor alignment between the cutter shaft and the axis of the casings when they have been placed in the holder. Through the judicious use of bits of spring steel as shims, I attempted to correct the issue. I have gotten it to the point that the variance is +/- ".0005 (the smallest increment my caliper displays.) My question is this: How square does a case mouth need to be for good accuracy? Would the above stated tolerance be acceptable? Thanks for any help