Should I trust my digital caliper?

T

Tikka223

CGN Ultra frequent flyer
Rating - 100%
74   0   0
Location
New Brunswick
I've got a crappy tire digital caliper. Should I trust it?

People keep saying that for load development you need to load +/- 1 "thousandth" so am I right in thinking that if the OAL at the lands is 2.435 then I should be going 2.436 or 2.434. I hope I have this right.

Either way, a .001 difference is quite small for something build in China and sold under all kinds of brands (Mastercraft, Cabelas, etc.)

What are you folks using for precise measurements?
 
I'm a machinist, and I wouldn't trust a +/- .001 tolerance to a caliper EVER, let alone a $15 cambodian tire one. Hell, i've checked a part with 3 different digital calipers from guys at work (one mitutoyo, one starrett, and one kurt) and ended up with a different measurement with each one. Checked with a height stand, and the best was off by .0005 (the minimum measurement that any of them would show). I remember when i was in school, our instructor told us, don't EVER trust a caliper to be accurate within closer than .002.

That said, I'm not so sure that .001 seating length is going to make a whole lot of difference. The caliper is probably going to get you "close enough". 0.1 grains of powder is probably going to make more difference than seating depth. Save your pennies, and buy a set of 0-3 micrometers off of ebay for $100. Or, save the 100 bucks, and put it towards a good scale.

Tikka223 said:
I've got a crappy tire digital caliper. Should I trust it?

People keep saying that for load development you need to load +/- 1 "thousandth" so am I right in thinking that if the OAL at the lands is 2.435 then I should be going 2.436 or 2.434. I hope I have this right.

Either way, a .001 difference is quite small for something build in China and sold under all kinds of brands (Mastercraft, Cabelas, etc.)

What are you folks using for precise measurements?
Click to expand...
 
Only as far as you can throw it. That being said, accurate measurement is much more dependant on the 'feel' of the person measuring, until you get into fully automatic cmm.(coordinate measuring machines). If you take your caliper and zero it before you use it every time, and measure with the same pressure (feel) every time, it should remain accurate. The thing to watch for with calipers is burrs on the tips of the ID measurement jaws. Make sure they are smooth, and that they come to a point.
 
There are more precise tools, but for most peoples reloading these will work fine. Change the battery 2-3 times a year and it will save you trying to figure out the wandering zero and random lengths. Sometimes they come new with dead batteries and you think they just aren't calibrated at all.
 
For reloading they will suffice just fine.

Unless you are using a comparator though, you are just pissing in the wind measuring to the tip of any bullet trying to get a proper and consistent OAL.

You would have to use 1 single bullet from any given lot to do your die setup, then if you switch to a different lot of bullets you have to do it all over again.
 
I've got a digital caliper, I prefer to double check the Lee Valley one I got as a gift a few years ago against the Mitutoyo I have. Also check it against a known dimension- in my world it's lock pins, every one of them is .115" diameter.
 
I have checked my Mitutoyo verniers against gage blocks on the OD jaws and they are right on (of course they only read in half thous) They cost around 280.00 but I think you can get a 6" pair more reasonable. I have seen the cheapies close up and still read .300 or so!!!
Micrometers are a more accurate tool but are harder to get a feel for if you are new to them so a "good " set of verniers may serve you better.
As pointed out above,If you do drop them (dont drop them) watch for slight deformation on the jaw tips that will hold them open when you zero them.
 
i use a mitutoyo as well that wasnt all that cheap when i bought it, but it works great and i trust it. as mentioned above, be sure that whatever youre checking is free of burs and other such things that will throw the reading off. same with the caliper itself, wipe the jaws down with your hand itll pick up the most amount of stuff and check it to make sure its zerod each time you take it out to use it. learning how much pressure to apply is something that takes some time, you can be out a few thou easily if you apply too much or not enough pressure. but i wouldnt trust the crappy tire special. theres a reason some cost well over 100 bucks and these are 15.
 
“The man with one watch knows what time it is. The man with two is never sure”

Better question is would 5/1000" make a diff as long as all are consistent.
 
I have checked my $15 Crappy Tire specials against some more expensive models and it was right on.

I have 2 sets of the CT calipers, one is very consistent......the other set, not as good.

The 2nd set is the one that turns on by itself when the caliper is opened/closed. The one I use the most is my best one and it needs to be manually turned on/off. I don't know if this has anything to do with it being more consistent than the other set or not.
 
I like the idea of testing it against a known length over time to see if it's consistent. I'm not sure what lock pins are ... any other idea for a good standard size to measure. What about loonies or something like that?

I'll give the comparator a go too and see what it says. The reason I wasn't using it before is because I was figuring out my OAL by putting a bullet against the lands and using the cleaning rod method to determine the OAL for specific bullets.
 
I use your method without a comparator. I start with a "reference" bullet, that has a length that is average for the box. I mark it, and record the length for future trials. When working a new batch, I measure the first bullet I'm going to use, and ensure it meets the reference length.
Of course, if you switch from one bullet lot to another, you've got to repeat the process. I'm disinclined to go to this level of effort, so I generally give myself some margin to the lands.
 
I use two Mitutoyo 6" calipers, one is mechanical the other is digital. The digital is more precise measuring to 4 decimal places, and I find it a bit easier to use, but both cost a bit more than $15.
 
You are probably seeking a chamber fit tolerance that is finer than the actual variation in bullet shape will always allow chambering. I'd opt for a bit more space to the lands and concentrate on cartridge over all length.
 
really, that canadian tire caliper is perfectly fine. Not like you need to worry about .001 play. I use one for reloading. #1.
 
Tikka223 said:
I've got a crappy tire digital caliper. Should I trust it?

People keep saying that for load development you need to load +/- 1 "thousandth" so am I right in thinking that if the OAL at the lands is 2.435 then I should be going 2.436 or 2.434. I hope I have this right.

Either way, a .001 difference is quite small for something build in China and sold under all kinds of brands (Mastercraft, Cabelas, etc.)

What are you folks using for precise measurements?
Click to expand...

Dial type is better unless you are doing tool and die. .001 is not significant if you are measuring OAL. But if you are measuring a precision fit part, then it matters.
 
Kryogen said:
really, that canadian tire caliper is perfectly fine. Not like you need to worry about .001 play. I use one for reloading. #1.
Click to expand...

Really? You're working up a load watching for .001" of case head expansion but miss it because the cheap caliper doesn't see it. Well you won't miss the expansion from the subsequent powder increment! Best just to use that thing as a case length gauge.
 
I've checked my cheap (CTC stainless) against my 1" micro & found it quite suficient to measure to the thousands.
BUT as pointed out somewhere above, the point of a bullet out of a mass produced box is not anywhere near consistant enough to use as a precise COAL measurement. In fact COAL measurement is only a good starting point to ensure cycling a round in the action as far as I'm concerned.
However unless your into super accurate benchrest rifles, your COAL with cheap dial calipers is fine for the average varmint/range shooter...IMHO :)
 
personaly, i don't use one at all- i have a LEE trimmer and just run that through as part of my case prep- the lee is already set for the right length, and the 4 and out rule takes care of the "stretching"
you can also get a case guage that works on the same principle- that takes the "guesswerke " out of using a caliper
 
You must log in or register to reply here.
Back
Top Bottom