I have been reloading for about a year now. I notice on this forum and many others that many posts discuss setting back the shoulder on a fired case by 0.001 or 0.002 inches. My caliper is rated at +/-0.0010. To make this measurement I wouldn't I need one that is accurate to at least +/-0.00050? Am I mixed up? I have been looking for a better one. I can't find any. Most will read to 0.0005 but that is not their accuracy. Even the ones that Sinclair sales are +/-0.0010. I have seen $30.00 dial and $250.00 digital. Where can I find a more accurate caliper for a reasonable price?

Here is an example of what I am talking about.


MEASURING INSTRUMENTS CALIPERS ELECTRONIC



500-196 CERTIFIED MITUTOYO 6"MY-CAL CERTIFIED
Maximum Measuring Range (Inch): 6
Maximum Measuring Range (mm): 150mm
Minimum Measuring Range (mm): mm
Minimum Measuring Range (Inch): 0
Resolution (Decimal Inch): .0005"
Accuracy: +or-0.025
Accuracy (Decimal Inch): +or-.0010"
Data Output: No
Battery Type: SR44
Manufacturer Part Number: 500-196 CERT

If it is realy + or - .025 or .0025?
.0005 is 1/2 of .001

I am reading the above spec as having a read out in 1/5,000ths of an inch, an accuracy of +/-0.025mm which is also an accuracy of +/- 1/1000th of an inch Am I wrong?

quote:

Originally posted by Game King:
I have been reloading for about a year now. I notice on this forum and many others that many posts discuss setting back the shoulder on a fired case by 0.001 or 0.002 inches. My caliper is rated at +/-0.0010. To make this measurement I wouldn't I need one that is accurate to at least +/-0.00050? Am I mixed up? I have been looking for a better one. I can't find any. Most will read to 0.0005 but that is not their accuracy. Even the ones that Sinclair sales are +/-0.0010. I have seen $30.00 dial and $250.00 digital. Where can I find a more accurate caliper for a reasonable price?

Don't sweat the small stuff man. Most any caliper made will work for the reloader. You just want it repeatable, doesn't matter if its measuring dead-nuts on.

OK! I just didn't want to make a mistake.
Thanks!

You are basicly right. Accuracy is that what it reads will ALWAYS be true within tolerance. (+/-0.025%). The resoution is "how small" a difference in size from "true" the tool can detect. (+/-0.0005") And the accuracy of the tool to its standard in decimals is 0.001"
The tool has to be able to detect smaller size variance then the desired size you want to measure to. This helps ensure the accurate repetablity of the tool to meet the claimed std. The tool is claimed accurate to 0.001" and the in reality is all we need to keep track of our loads. The fact it is accurate to 0.001" accually doesn`t mean a whole lot in our useage as long as it repetes. The depth we seat our bullet can be 2.220" in TRUE ACCURATE lenght or 2.210" that our tool reads as 2.220". As long as the tool keeps repeteing the measurement as the same we will be fine. Even in max case lenght there is room for a 0.001" or so error.

Get two sets of pin gauges, .0600" to .2500" and .2510" to .5000"
http://www.use-enco.com/CGI/INPDFF?PMPAGE=232&PARTPG=INLMK3&PMITEM=240-0142

Practice measuring the reference pin gauges with the DIAL calipers until your eye can interpolate to get .0002" accuracy on outside measurements.

Dial calipers are never very accurate on inside measurements. Use the pin gauges for that.

With the pin gauges you can measure:
1) the donut inside the case neck at the base of the neck.
2) the neck diameter of sizing dies
3) the neck diameter of chambers
4) the diameter of primer pockets
5) the bore diameter of barrels

Thanks for the good advice.

Buy starrett in measuring tools.

Good calipers are limited more by technique than by accuracy. Even if they were supposedly to ±.0005" few humans can take advantge of it because of the poor touch you have with calipers.

quote:

Originally posted by Game King:
I notice on this forum and many others that many posts discuss setting back the shoulder on a fired case by 0.001 or 0.002 inches. My caliper is rated at +/-0.0010. To make this measurement I wouldn't I need one that is accurate to at least +/-0.00050?

If you are measuring the amount you are setting the shoulder back when you resize the case it is much easier to use a case micrometer like the RCBS Precision Mike. This measures from the base to the same datum point on the shoulder every time and is calibrated in .001s of an inch. You just insert the case in the base part of the device, screw the upper part on over the neck until it touches the shoulder and read it just like a micrometer. Midway has them and some sizes are on sale until the end of the month.

It is easy to measure the overall case length with a caliper but, at least for me, very difficult to measure the shoulder set back because I can't find the same point on the shoulder every time.

quote:

Originally posted by Game King:
I notice on this forum and many others that many posts discuss setting back the shoulder on a fired case by 0.001 or 0.002 inches.

There are some very technical reloaders on AR.
If you are just loading standard hunting/shooting rounds, you needn't measure them at all. It's only on the USA forums that I've ever heard the term "bump the sholder back".
The practical world couldn't care two hoots how many thou. the shoulder is bumped, and a lot of people do a lot of neck sizing where the shoulder isn't bumped anywhere.

So if you want or need to FLS you should do it only as much as necessary, so that the case just fits in the chamber. This is done by feel of the bolt closing on an empty sized case.

Some like to just feel a slight tightness, or you can screw in the die just a tiny bit more.

Over here, we make out we are squeezing the case sides in as they get tight just above the head.
If you fellers arn't squeezing the sides in, why do you need resizing lube?