6 inch dial caliper form PA.

[Polish-Jack]

I just bought a 6" Dial Caliper from Princess Auto for use in reloading. The specs on the box state that is has a resolution of 0.001" This is what I need.

Lyman 48th Ed. states that a 9mm Luger case should be 0.754" in length and that the case length is very important because 9mm headspaces from the mouth. I took apart five factory 9mm Luger 115gr. Winclean rounds and measured the cases. All five cases measured 0.748". A 0.006" difference. Did I get a bum caliper or is this measurement correct. I made sure the caliper was calibrated and I measured twice.

 

[45atv]

caliper

i'm a machinist and calipers are not very accurate. .004/.005 gets you close. a micrometer will tell you exactlly. find someone with o-1 inch mic and measure one case and compare. or measure something that you know is a certian size, like a 1 inch shaft and see what your caliper reads.

 

[ElmerFudd]

0.754" is the maximum case length and the trim-to length is 0.744" So while your calipers might be off by a bit the cases appear to be right in the middle. I think you will find that you don't ever have to trim 9mm brass as it is unlikely to get past the maximum length with repeated reloadings.


Fudd

 

[deanml]

Verniers are accurate enough if you get good ones. Don't waste your money on crap. A bit of practise could be the issue. I've seen a lot of people in industry who cannot use mics or verniers, they look at the value they are getting while they measure and settle on something that looks good because they can't get repeatability with it. Check it against a know radius, like a drill. Don't look at the dial when measuring it. Measure by feel then look at the dial, you should be well within one thou with a bit of practise. Once you have a good feel for the tool you should be fine. P.S. measuring something twice is never enough for an accurate reading, and clean your measuring surfaces every time you use it. Cheers, DML

 

[Slash5]

If you are trying to test your calipers, use bullet diameter. A jacketed .308 bullet will be within a half thou or so, usually - no more than a thou out.

 

[ElmerFudd]

Hey. Yes, it is out of my Speer #13 Manual. But I just checked the Lyman 48th and it lists a trim-to length of 0.751". But I think you will find that for most cases the trim-to is about 0.010" less than the max length.

I just measured a few range pick up 9mm brass and they ranged from 0.744" to 0.746". Don't know how they got in my pick up bag because I don't even shoot 9mm!

Hope that helps,


Fudd