Digital Calipers - 2 vs 3 decimal places

OEM

OEM

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Hello:

I was just wondering how critical it would be to use a digital caliper with accuracy to 2 decimal points and not three (as I see most specs are). I ask cos I'm thinking of getting one that has a rated resolution of 0.01" / 0.1 mm, but I see that the recommended cartridge length of my 303s is 2.222.

Could some of you experts weigh in with your thoughts on this matter please!
 
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OK thanks. I'll pop over to Princess Auto tonight. BTW Mark, reloaded the first 10 of my fire-formed brass with 35 and 36 Gr Varget. I'm using this as my starting point and going from there. Quite pleased with how smoothly the reloading went. Took about 2 hours to reload those 10 though...cos I was going through every step maybe 10 times, just to be sure. Me and my buddy must've measured the powder hundreds of times before we committed!!
 
"...was going through every step maybe 10 times..." You'll get over that.
"...accuracy to 2 decimal points..." Close enough. A couple thou of case length isn't going to matter much for hunting ammo. Neither will 5 thou of OAL. Max OAL is 3.075" for a .303.
 
Calipers are generall accurate to +/- 0.0005". Even the digital ones (except expensive ones, but even then) can only really be trusted to 1 thousandth. If you want to be sure, you have to get a micrometer, and that will run you a pretty penny. Those are accurate (when calibrated) to +/- 0.00005.
 
Meph said:
Calipers are generall accurate to +/- 0.0005". Even the digital ones (except expensive ones, but even then) can only really be trusted to 1 thousandth. If you want to be sure, you have to get a micrometer, and that will run you a pretty penny. Those are accurate (when calibrated) to +/- 0.00005.
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I would trust good (Starrett/Mitutoyo) Calipers to +/- .0015". A good MIC to +/- .0005" and a good Vernier MIC to +/- .0001". And this is ONLY if you use it for more than just reloading on Sundays. If you have no other experience with precision measurement move the decimal another place to the right.
 
Learn to use a vernier. Once you get the hang of it they're no harder to read than a digital and the batteries never go dead.


**I just noticed I'm an official 'regular member' now, I'm so proud!**
 
Thanks for the thoughts guys. I only wanted digital cos I can't see the regular ones. I'm pretty sure I can learn how to read the regular vernier. Problem is, I could hardly see the numbers!
 
The ones you can get from Canadian tire aren't bad. I even use mine at work, just be prepared to buy lots of batteries. The batteries don't seem to last long but you can get the unit for $25 on sale.
 
Those from CT can be had for $15 on sale, and if you remove paper manual from the case, your batteries will last 100x+ longer due to power button not being pressed when you close the case...
 
cdnredneck_t3 said:
I would trust good (Starrett/Mitutoyo) Calipers to +/- .0015". A good MIC to +/- .0005" and a good Vernier MIC to +/- .0001". And this is ONLY if you use it for more than just reloading on Sundays. If you have no other experience with precision measurement move the decimal another place to the right.
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Most of the good calipers will do +/- one thou, even less if you know the sweet spot pressure to lock them. And really though, I've taken really dead on Mitutoyo vernier MIC measurements, they're accurate to the ten-thou, not to two ten-thous. Then again, I'm working steel all year and taking measurements by hand a lot.
 
OEM said:
Thanks for the thoughts guys. I only wanted digital cos I can't see the regular ones. I'm pretty sure I can learn how to read the regular vernier. Problem is, I could hardly see the numbers!
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What about a dial caliper? They're easier to read than a Vernier scale and don't need batteries like a digital caliper.
 
Meph said:
Most of the good calipers will do +/- one thou, even less if you know the sweet spot pressure to lock them. And really though, I've taken really dead on Mitutoyo vernier MIC measurements, they're accurate to the ten-thou, not to two ten-thous. Then again, I'm working steel all year and taking measurements by hand a lot.
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Me too. Make my living doing it in fact. I stand by my original post.
 
I would buy a good caliper and buy once rather than buying sh*te from PA. My PA torque wrench ate a set of TPS rings because they took a dump and I was asleep at the switch. I have a Starrett and I'm confident that it'll last plenty long that it will pay for itself.
 
I bought a $200 Mitotoyo about 15 years ago and it functions like the day it was new and it's only on it's second battery. Being a millwright I use it almost daily, so it was worth the investment. For reloading, the ones that Canadian Tire or Princess Auto sell are fine. I'm just trying to think if I've ever seen a digital one that only goes to 2 decimal places (1/100th of an inch)....I don't think I have.
 
cdnredneck_t3 said:
Me too. Make my living doing it in fact. I stand by my original post.
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What do you do? And you don't trust them that much? I've double checked in some cases with a granite surface plate, gauge blocks and a... Don't know the English term, I do all my stuff in french, I'll try to translate (comparateur a cadran a bascule) a toggle dial indicator or comparator and it was pretty much dead on at 21C.
 
Meph said:
What do you do? And you don't trust them that much? I've double checked in some cases with a granite surface plate, gauge blocks and a... Don't know the English term, I do all my stuff in french, I'll try to translate (comparateur a cadran a bascule) a toggle dial indicator or comparator and it was pretty much dead on at 21C.
Click to expand...

Meph said:
Calipers are generall accurate to +/- 0.0005". Even the digital ones (except expensive ones, but even then) can only really be trusted to 1 thousandth. If you want to be sure, you have to get a micrometer, and that will run you a pretty penny. Those are accurate (when calibrated) to +/- 0.00005.
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you don't use calipers to measure critical dimensions less then +- 0.005

Yes, that includes my $275 dollar mitutoyo digital "half thou" reading calipers. For you to say you can read tenths with a caliper is just f$#king stupid lol


IF you ever need to measure to half a thou (doubtful) you will want to use a micrometer (or surface reading indicator setup; grinding?) . I have a nice mitutoyo 0-1 digital mic that claims to measure to 0.00005 (1/000005 that I trust to measure to 0.0005 lol.)

Beyond that, ccm or a comparator. neither of which i have (or need)

To the OP, if you want to accurately to one thou on an OD, grab a decent quality mic, kar is quite reasonable.
 
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here is a quick visual reference crappy digital pic: what i trust; most to least

not shown for the first item is the surface plate and indicator holder (0.0001 dial indicator)

measure.jpg


the mitutoyo 0.001 calipers at the bottom i use to measure and mark stock for cutting in my bandsaw lol
 
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