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Richz99 02-21-2011 01:55 AM

Caliper Accuracy Issues
 
Need some helpÖ

Iíve decided to get into reloading, so I bought a few things yesterday including a dial caliper and a Sierra reloading manual. Iíve been wanting to start reloading for a few years now, and Iím finally taking the plunge.

So anyway, Iím reviewing some of the data in the manual at the same time Iím measuring some of my ammo here at home, but the numbers donít match?! My problem is that Iím concerned that my caliper isnít accurate, but I donít really have a way to verify without getting a second caliper.

Here are a few examples: When I measure the bottom (rim?) of the .45 ACP case, I come up with .476Ē, but the book says it should be .480Ē. The same holds true when I measure the rim of a .357 magnum case, I measure .434Ē, but the book says .440Ē

Now, if the readings were always consistent (say .005 off), I could conclude that my caliper has issues, but sometimes the reading is spot on. For example, when I measure the bullet for a 7.62x39 cartridge, I get a value of .311, which is exactly what I would expect.

So what do you folks think? Is this normal, or do I need to replace this caliper? If itís normal, do the values in the book represent the max allowable?

Thanks in advance for any help.

JonM 02-21-2011 02:13 AM

not all brass is the same. outside dimensions may vary slightly from brand to brand. measure the diameter of a known bullet. your caliper should be ok. just zero it out and get after it.

aandabooks 02-21-2011 03:54 AM

What brand caliper did you buy? Calipers generally are not the most accurate choice for measuring round items. If you want to get the most accuracy you need to buy a good 0-1" micrometer. Calipers rely too much on the operator being square to the part and using a consistant pressure time after time.

That being said, calipers are faster to use than micrometers and if you purchased a digital set, they are easier to read at a glance.

Richz99 02-21-2011 04:52 AM

It's a Lyman dial caliper; analog. I usually prefer analog over digital when it comes to precision measuring. Call me old school...

noylj 02-21-2011 07:22 PM

Consider manufacturing tolerances and then look at the case diagram. Do you see min/max tolerances? Do all you cases measure exactly the same?
Measure case length. You will find that all your pistol cases measure less than the case drawing shows.
Per SAAMI, the body diameter is x.xxx +0/-0.006.
Go to http://www.saami.org/PubResources/CC_Drawings/Pistol/45%20Automatic.pdf
and
http://www.saami.org/PubResources/CC_Drawings/Pistol/357%20Magnum.pdf
and study the drawings. There is no +/-, everything is +0/-x.xxx.
We do not live in a perfect world, so dimensions do vary.

c3shooter 02-21-2011 10:10 PM

Flashback- the day I came back from TDY, and found my bride had glued and clamped a broken widget using my Starret 0-1 mike. :eek:

If you doubt accuract of a caliper or mike, use a known object, such as a feeler guage. Brass WILL vary.

aandabooks 02-21-2011 10:55 PM

Have never heard of Lyman. Calipers are generally sold with a +/- of accuracy stated. Get a gauge block so that you can periodically check your calipers for accuracy.

Eric0424 02-22-2011 02:11 AM

As mentioned before brass case dimensions will vary from what's listed and from one brand to another. They may even vary from one lot to another of the same brand. If it's any help, I just measured the rim (yes it is the rim you measured) on four pieces of Remington 357 brass and four Federal in 45ACP, the 357 has the same number you measured, the 45 measured .475". I get the same numbers with three different calipers, Fowler, some China knock-offs and my Browne & Sharpe. They all read the same measurements.

Your caliper sounds like it's fine and you shouldn't have any trouble measuring round objects down to a .001" accuracy as most calipers are designed, including your Lyman.

Quote:

Originally Posted by aandabooks (Post 450613)
Have never heard of Lyman.

Never heard of Lyman?? They produce reloading and shooting accessories, and equipment.

Lyman Products Your Primary Source for Reloading Equipment

Richz99 02-22-2011 03:26 AM

Eric,

Thanks for the help; I really appreciate it!

Now it looks like I have a lot of reading ahead of me to ensure my first reloads don't blow anything up :)

rjd3282 02-22-2011 06:00 AM

Quote:

Originally Posted by c3shooter (Post 450591)
Flashback- the day I came back from TDY, and found my bride had glued and clamped a broken widget using my Starret 0-1 mike. :eek:

If you doubt accuract of a caliper or mike, use a known object, such as a feeler guage. Brass WILL vary.


I know that is sad but still a little funny. :D


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