I have been trimming cases and notice as I spin them in the calipers I tend to have a very slight deviation usually on one side. Since noticing I have been trimming, unlocking case and rotating, then trimming again. This has caused them to be more square but I will still occasionally have an ever so slight deviation (ie: 1.910 and 1.9105 on one side). I don't think this is an issue seeing as my results firing tend to be very good, however I am wondering if this is something anyone else notices and whether its worth trying a different trimmer or just leave it alone. I guess for world class competition guys this is probably taken into account and I'm far from there but I am loading to be sub 1/4 MOA and if I could improve that by simply rotating while trimming or using a different trimmer it could be worthwhile.
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Trimming cases and being square
- Thread starter Calien45
- Start date
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- case trimming trimming
I understand, that it is. That's also after rotating the case. It's obviously more if I don't, have seen as much as 1 or 2 thousands difference before. It just simply bugs me that they aren't squared up. Whether it makes a big enough difference to notice, I don't know.
Square to the half thou is pretty square.
Put a piece of tape over the half thou spot on the calipers so you don't see it, continue to rotate the brass in your trimmer, be happy you were smart enough to buy primers when the getting was good and go shoot.
Put a piece of tape over the half thou spot on the calipers so you don't see it, continue to rotate the brass in your trimmer, be happy you were smart enough to buy primers when the getting was good and go shoot.
If I were to make an ordered list of the things that mattered (in that they might make a measurable difference in accuracy or precision of a well-trained shooter under any reasonable conditions using good equipment), this would not be on the list. It would be on the other list with things like the color of my shell holder trays and the type of music playing in my loading room while the tumbler is running.
Your calipers are not that accurate. Just because they indicate with a resolution of 0.0005" does not mean they are that accurate. Even high-quality Mitutoyo digital calipers have a Scale Shift Maximum Permissible Error (MPE) of +/- 0.001". That means it could be a thousandth off in either direction. What's more, the MPE for "Partial Surface Contact" is +/- 0.002". What you have measuring the thin brass edge is partial surface contact.
If you're using a sub-$100 caliper, the accuracy is probably worse.
Have you checked the calibration of your calipers? A checker that will verify linearity of the scale inside and outside costs many thousands of dollars -- worth it for a metrology shop, but impractical for us reloaders. You can still check it with a Mitutoyo rectangular gauge block -- about $20 plus shipping.
If you're using a sub-$100 caliper, the accuracy is probably worse.
Have you checked the calibration of your calipers? A checker that will verify linearity of the scale inside and outside costs many thousands of dollars -- worth it for a metrology shop, but impractical for us reloaders. You can still check it with a Mitutoyo rectangular gauge block -- about $20 plus shipping.
My old Lyman hand trimmer did the same thing from the day it was new. Used it from 1989 until a year ago where it was replaced by the little Lyman electric cutter that spaces off of the shoulder.
Measuring to see if it's perfectly square?
Not even back when I shot Benchrest did I worry about something like that.
Measuring to see if it's perfectly square?
Not even back when I shot Benchrest did I worry about something like that.
I like to sort my brass by the width and depth of the extractor grove. 
Carry on O.P. i don't even trim my brass very often anymore. I get much more variance in length than that from one case to the next. No big deal.
Carry on O.P. i don't even trim my brass very often anymore. I get much more variance in length than that from one case to the next. No big deal.
WOW....we put men in space with looser tolerances than this!!
let me say it again.....RELOADING.....THE MOST OVER THOUGHT THING ON THE PLANET!!!
let me say it again.....RELOADING.....THE MOST OVER THOUGHT THING ON THE PLANET!!!
It really does get over complicated. I always laugh when someone says they need to have zero distractions when reloading. 100% attentions must be paid. I usually dick around on line while my Chargemaster is running, or watching TV while I prep cases.
Yesterday while messing around reloading in between running back to the computer intermittently for work I watched the dirty dozen, et & quigley down under.
