These replies are all very interesting. Thanks for sharing your knowledge.

Is there a reasonable and inexpensive way to check a caliper or micrometer to see if it's accurate? Something that's reasonable for the average reloader to do occasionally?

I saw gage block sets for sale, but they're fairly expensive. Is there a cheaper way? Maybe a smaller set, or individual blocks?

Calipers, not really. You can zero them, and thats about it. Or check them on a 1-2-3 block to see the accuracy across its scale. Make sure when you gently (!) Close your calipers on themselves, hold them up to the light. Ideally you shouldn't see any come through between the jaws. If you do, make sure it is uniform from the top of the jaw to fhe point. If not, the jaws are deformed, and/or out of parallel if you wanted to get crazy, there is cant screws on the top of the body of the caliper, on on either end. Can screw/unscrew to change the cant of the jaws as needed. Honestly I wouldn't rerecommend this if you dont want to fuck them up more, not easy.
Micrometers are way more precise and require a more precise means of "zeroing", which is not the same as "calibrating". To truly calibrate a mic, you wont be doing it. However if yiu just use them at home and want to make sure they are tits, you can use the same calibration method the pros do but wont be certified of course, which you wouldn't care about anyway.
To check zero on a 0-1" mic, run it down on itself, carefully! Check zero, much like a caliper. If mic was bought with a box, shouod have a 1" master. Run it up to 1" and check to master. Mics can get backlash in them.
For larger sizes, they obviously cant close on themselves. So co check zero, you need the correct master, such as a 1" for a 1-2" mic and so on. Also, if came with a box, should have a couple spanner type wrenches. If a mic doesn't zero out, you can use the wrenches to hold the body stable, while the other can turn the anvil portion to zero it out.
Again, zeroing, is different than calibrating. And even if a mic is off you can still zero it using the calibration method with the same results.

**edit**
here is a 0-3 Mitutoyo digital mics. These are shop supplied, mine are nicer, but not allowed to have personal tools here. You can see the two green masters. Those are a 1" and 2" master for checking the 2" amd 3" mics.

Good stuff, Kyle. Impressive.

You can buy individual gauge pins from like MSC, ENCO, or EF Bailey. They are 3-5 bucks each I think. Maybe less.

You could get ones that are the same diameter as your bullets. .308, .224, whatever they happen to be. Keep in mind that gauge pins are typically .0002 or so under the stated size as to fit in the hole they're measuring and not be a press fit.

That would be about the cheapest I would go, and .0002 isn't going to kill you for your application.

No need for a digital mic, IMO but thats up to you and if you're comfortable reading a standard micrometer.

Here's an example.
http://www.mscdirect.com/product/detail ... 1&fromRR=Y

And here's a mitutoyo micrometer.
http://www.mscdirect.com/product/details/06231658

About 115 bucks, not too bad. The SPI was 80. Not sure what a Starret will cost you. I don't fuck around on measuring equipment(its my profession), but even if this were only for my guns I think I'd at least buy the SPI.

Great tips, Chris. Thank you. I think I'll need to do some online shopping over the weekend....

My job consists of measuring parts compared to the drawings and we have always used the cheap Cen-Tech models from Harbor Freight. They get "calibrated" every 6 months to calibration blocks that range from from .050" up to 6". The farthest any of them have been off has been .0005", just like the Madpick found in his experiment. And if that's good enough for an ISO 17025 accreditation, it's good enough for me!

Sorry Jim, but there is a reason no self respecting shop uses calipers like that. Not sure what your job is, lr what parts you're checking to a blueprint, but that doesn't fly in the machining world. Ive seen guys have them, but they dont use them, or for very as they sre either told to by nicer calipers or they realize the difference and do so on their own.
With calipers it isnt all just it being "calibrated" to ISO standards. Most can be. How long will they hold that zero, how smooth do they operate, if you open and close them on the same part 100 times will they read the same every time? Some do, some dont. Not uncommon for calipers, especially cheap ones to "lose" their way on the scale and have to be re zeroed, or just not repeat the same number on said measurement. The fact they only vary .0005 is sort of irrelevant as they can onoy be certified within .002".
Steve, chris is right. If you buy gauge pins, pay attention whether they are + pins or -. They run .0002 variance from size accordingly. Of course, buying the mic masters arent very expensive either. Same as Chris, this is my livelihood and therefore I spend the bucks the buy the best, not necessarily neededed for all applications though. Just try and buy Japanese if possible, or Starrett.
Depending on what you're doing I have anything and everything you could need just sitting around currently. I have to use shop supplied and outside calibrated shit. I would be willing to let you borrow as needed if it came to it.

As smooth as my Cabela's calipers feel to me, and as nice as I used to think they were, it's true that they need to be re-zeroed quite often. They're not off by much, just a half a thousandth or whatever, but it does tell me that they're not spot-on.

Of course this thread get's started just after I bought my first caliper, LOL.

I didn't do a whole lot of research before buying but based off the video review on amazon I went with this igaging absolute zero. It's the middle of the road but inexpensive enough in case I need something better down the road.
http://www.amazon.com/gp/product/B00INL ... UTF8&psc=1

It finally arrived yesterday after a Prime shipping debacle. Pretty hefty device and always returned to zero.

I have a set of import mics that I got in high school. They were accurate enough but fell apart in about a year and a half of shop use. They're still in my box, but I never use them.

Also. ISO isn't a universal quality standard that lays out your quality policy for you. ISO just means you have a detailed quality policy in place and that you follow it.

At least to my understanding. A mic being off .0005 where I work would get thrown out. That's half of most of our tolerance.

That was a pretty interesting review. Here it is:

"plus a bunch" on this ^^^^^^

A micrometer is the only way to measure things when you want resolution below .001".

Also, when comparing precision measuring tools the only way to be sure your measurements are accurate is to have both the tool and the "standard" in the same position with each. When I worked in a precision shop many years ago most of our tool comparisons were done by holding them in a bracket sitting on a "surface table" with the "standard" held in another bracket so they had the same relationship to each other. A long way of saying "the object being measured has to be square with the tool.

Rather than using a bullet I'd go buy myself a dowel pin that has been ground with parallel surfaces (bullets vary along their length) and use it for comparison purposes.

A good reloading bench has three measuring tools. A "good" (but not necessarily expensive) caliper, a Standard Micrometer (0-1") and a "Tubing Micrometer" (for measuring case neck thickness).

Often the standard mic will come with a calibration piece, usually a precision ground piece about 1" long, that can be used withe the other tools to check accuracy.

Oh, just a follow-up to this old thread . . . I recently bought this micrometer:



https://www.youtube.com/watch?v=GRfTRsspOnw

Lo and behold . . . my .308 bullets are actually 0.308" in diameter!



I haven't given it any serious use yet, and it's my first micrometer, but so far I'm pretty happy with it.

Ohhhhhhh, calipers. K I thought Steve went out shooting again and this was a "tale of 3 chronographs. "