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Old 09-09-2021, 01:18 PM
jem102 jem102 is offline
Join Date: Jun 2021
Location: East TN
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Originally Posted by BLUEDOT37 View Post
Fired cases are shorter because the case has expanded & the case walls are bowed out.

Once you size them, & straighten the case walls out, the change in the measured length is proportionally longer to the difference which varies with the load's pressure & the chamber it was fired in.

Size the cases first, then trim them.

If needed, reduce the diameter of your trimmer's pilot to fit the sized case.


The above is what I believe you will find correct depending on what you are trying to accomplish.
It would be an easy step this next time out to "group" the various case lengths, within reason, reset the crimp for each batch and test them on paper by overlaying a fresh target for each case length group dead on top of the previous target. Radical crimp variation can cause accuracy issues but as already stated by others not a deal breaker in the vast majority of cases. when you peal down to the first target I think you will pleasantly surprised to find the overall mass group to be quite consistent with no outliers that would cause a poor hit unless you "pulled" that particular shot so make notes as you go round by round. This should reassure you of the "no trim needed". Having said all this "I" enjoy my handloading and do not find it a chore to trim my cases when I start to see the case mouths are rolling into the groove too high on the wheel gun as I have determined the max COL with a 10 case average when the brass was once fired with a given bullet. When "plunk" testing for the auto if the rim is past flush with the hood I will knock a few thous off that lot.
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