Yesterday I set out to process some 7mm Rem mag brass. Step one was selecting the correct bushing for the Redding Competition Neck Sizing die. To do so, you measure the neck wall thickness. Double it. Add the bullet diameter, and deduct two or three thousandths. The result is the inside diameter bushing size. Most folks would just assume the bullet diameter was .284" (7mm). I, being a bit OC, measured one. The result was .278". I thought "A 270 bullet (.277") got in the wrong box, plus my digital caliper is off .001". So I measured a few other 7mm bullets from other boxes and continued to get .278". I zeroed the caliper, several times. I checked everything I could think of. Still .278". Well, you say. Easy peasy. Just replace the caliper. Not so simple. Now I am trying to determine when the device went south, and what measurements I made in the meantime that could have unfortunate consequences.

Lessons learned: One can never be too careful, and Murphy never sleeps.

Yep

I've been through probably a dozen sets of 6" calipers on the job

They wear out....the less expensive ones go fast imo

I still have my original 6" Brown and Sharps and Starretts I bought in 87 and 88 as a bucket full of lesser tools have fallen.....some literally have fallen to the floor

Setting zero or checking zero is fine but a check now and then in the outer range of all you measuring tools is essential

I have 2 sets of Chinese 6" calipers that I have custom ground to fit into tight spots and one pair I scribe lines with that Ive re-ground the tips so many time they are getting stubby

Does it read zero when the jaws are closed? If so, and it measures .278 when it should really be .284, then throw it as far as you can and buy a new one.

Sometime a year or so ago I was on the phone with Sinclair about something and somehow we got on electronic calipers. All my Starretts are older dials but test right on.

So I bought a pair of the so called good Chinese ones for reloading. I don't know what brand. During the first use I went and threw them in the trash. Yes I could have sent them back but it served me right for buying them to start with.

My neighbor was working a shop job and things wouldn't fit and we looked at it and I said I bet the calipers are off. I went and got a Starrett digital mic ( because while I can read the dial calipers good, I can make an error with the mics) and his Chinese calipers were way off. He asked about having them calibrated and I said I would just get a new set.

Just a week ago I looked at a set of Mitutoyo absolute 6 inch digital calipers to use really just for reloading. These look pretty nice But I went out and got the gauge blocks and tested several of my pairs as being dead on and decided to just stay with the ones I have.

Even the newer Starretts have plastic in them that wears out. I asked them about service and they said to just replace them.

So keep a gauge block(s) or set handy and check them from time to time.

Good advice, Tex. I had a Starret digital that failed (lost accuracy). Called Starret about repair or warranty. I guess they're still laughing.

Ah yes, the digital versus analog thing again. We have been so programmed to believe that "digital means more accurate " and "electronic is better" that we will probably never recover. I have a Craftsman dial caliper from 1972 that is still accurate. I have a Redding powder scale from 1995 that is likewise both accurate and sensitive. I have no digital measuring devices at all. Some of my Mikes are over 40 years old and wonder of wonders I have never had an electronic component fail or needed to replace a battery in any of them. I know people who don't even know what a Vernier scale is let alone how to read one. Welcome to the new age, I guess....

Oh, and another old time rule: when you need to measure to .002" or less accuracy, put the calipers away and use a micrometer....

While this isn't the biggest gremlin ever I opened a completely new box of Federal GMM 215 Magnum primers. I haven't seen a new one of those in a while either lol.

I get out a tray of 100 and look at the label and it says GMM Large rifle. Huh?

So I remove and examine the others in the box and there are 9 boxes of Mag 215 and the one stray Large rifle.

While nothing bad would have resulted from it use, it was still odd.

It pays to check your work in reloading.

For measuring bullet diameters you need a more accurate tool than the normal slide calibers we use to measure cases.

We use a screw type tool that goes to 5 places of decimal when we make our bullets.

As mentioned, when dealing with 3 decimal places use a micrometer.

However, you can also take your measurements with calipers of any flavor and check them by using a mike on the caliper internal jaws.

Pushing 30 years now as an injection mold maker

Reading post that state calipers are not accurate brings up two points

The tool quality

The person behind the tool

I can always stack up jo-blocks and get my tenth indicator out then grind and drag

Those tall stacks of jo-blocks on my clean pink granite Starrett look sharp when the boss is showing off the shop with customers......god forbid any one uses dial calipers

Funny

I checked the digital caliper with a gauge block, and it indeed is off. No way to correct it, I'm sure. I may still use it for go/no go type stuff because it's error is constant.

I have another caliper, a cheapo dial mechanical that used to live in my range box. Although plastic, it's accurate to.001", good enough for nearly all reloading tasks. (I do have a one inch micrometer.)

For reloading accuracy, about half an RCH seems to be adequate.

Incidentally, what's with the term "pair of calipers"? Is that akin to "pair of binoculars"?

Anyway, I like to hear what smiths and machinists have to say. It tends to reduce my ignorance. Thanks.
Brice

quote:

Originally posted by Brice:
I checked the digital caliper with a gauge block, and it indeed is off. No way to correct it, I'm sure. I may still use it for go/no go type stuff because it's error is constant.

I have another caliper, a cheapo dial mechanical that used to live in my range box. Although plastic, it's accurate to.001", good enough for nearly all reloading tasks. (I do have a one inch micrometer.)

For reloading accuracy, about half an RCH seems to be adequate.

Incidentally, what's with the term "pair of calipers"? Is that akin to "pair of binoculars"?

Anyway, I like to hear what smiths and machinists have to say. It tends to reduce my ignorance. Thanks.
Brice

And a pair of underwear / slacks / pantyhose and "lovely pair" (of ta-ta's)

This former die-maker says plastic calipers scare me. Because of how just minor variances in how much force is applied WILL change a measurement, I've never bothered even looking at a pair.

By the time I've put away my tape measure, I'm looking for real numbers ... not guess-work.

While I was moving, my precision stuff got stolen (0-6" mics, 18x24 Starret pink 2-ledge surface plate, comparator stand, Mit calipers). I still have my 81 piece set of shop grade jo-blocks but sticky-fingered "helpers" helped themselves to my better tools.

So, being new to reloading, it looks like it is also time to re-tool. You'll find me in the aisle marked "Starret, Mitutoyo, Sherr-Tumico and SPI". I don't have access to a surface grinder, so I'll have to buy precision since I can't make it.

While we're on the subject of gage blocks ... they are the wrong tool to calibrate a set of calipers ... use a gage pin, instead.

Gage blocks are extremely flat ... and won't alert you to splayed jaws. For that, take something round and hard (shank of a new drill bit works well) and measure at the tip of the jaws and at the inside just before the gap made to allow for burrs.

Use very light pressure. The reading, no matter what it actually says, should be the same (but probably isn't). If the difference is enough to be significant to what you are doing, take note to only use the jaws at the tip from now on.

quote:

Originally posted by ted thorn:
Pushing 30 years now as an injection mold maker

Reading post that state calipers are not accurate brings up two points

The tool quality

The person behind the tool

I can always stack up jo-blocks and get my tenth indicator out then grind and drag

Those tall stacks of jo-blocks on my clean pink granite Starrett look sharp when the boss is showing off the shop with customers......god forbid any one uses dial calipers

Funny

When is the last time you had the Starret re-calibrated? (grin)

I once had to work out to 30 millionths in titanium (munitions for the US gov't.). After proving to the boss that the computer couldn't make the part (made 100 pieces his way, none of them good), he let me do it my way. 10,000 pieces later, I had a total of ONE reject.

This can be a VERY picky trade. ;-)

The defeats are total. The victories last a lifetime. Good place to learn honesty.

I was measuring some bullets recently with my digital calipers, used to have a top brand pair but kids dropped them and broke the screen so just replaced them with a cheap probably Chinese pair, anyway the bullets were all measuring .004 to .005 thou under size.

I take the button battery out of my calipers when not in use and the battery lasts a long long time whereas before it always seemed to be flat within a month or so even when switched off.

I turned the caliper off and then back on again and then left it turned on for 4 or 5 minutes without moving the jaws, re-zeroed and re-measured the bullets, they all came up to the correct dimension.
I know many instruments (some we use at work) have to be turned on for a while before calibration and use to bring the electronics up to temperature and stabilise them before using i.e. turn on and don't attempt to use the instrument in that time.

Worth a try for anyone having issues with their digital calipers.

Bullets need to be measured with a Micrometer, not calipers for goodness sake. I like a digital mic or std. mic, they both work for me..and its smart to do a series of tests on a bullet and take an average I've been told, but seldom find it necessary with my mics.

It doesn't sound like the Redding collar system is all that great..I mic the expander ball in my RCBS dies or whatever, and usually grind off a thou or two on most calibers to give a lightly snug fit that won't allow the bullet to turn in the case or be pushed back with some force..then use a powder that fills the case to light compaction, and that voids a crimp on most calibers and only takes a very light crimp on double rifles and the really big bores, but I just crimp them to be safe as I have never set a bullet back or forward without a crimp when so set up, and I tested quite a few rounds without the crimp on my big bores over the years, so I'll call the crimp optional, even on the big 500. but to each his own on that.

eagle27 - you are on a roll mate! Spot on! That is 2 complements from me today!

Mitutoyo any one. I have the 8" digimatic. Couldn't ask for any better. I use the Mitutoya tubing mic for case necks. Not digital but very very precise. No doubting one's self.

Yes, I have a Mit; good for 90% of what needs measuring and for the last ten percent, I have a few of old school micrometers.

glad I came in today. H47 helped me realize that my degenerative slide into geezerhood has halted at 'curmudgeon'. been like this for a while.
my experience with digital scales is that they should be on for 30? minutes before calibrating. and sometimes need to be calibrated twice in short succession. Digital calibration is an approximation process towards correct measurement so calibrating twice is better.
I use no digital devices in my reloading.

rcflash,
Your correct, but my old hand mics are just about as bad when its time to really cut hairs, One gets a little different reading everytime, so take 5 or 10 and get an average with either might be best. It's also best to hold them in a vise of some kind IMO.

Hold a mic in a vise? Not in my line of work

Your mic gets different readings each time?

It needs the thread collet adjusted or pitch it in the trash

quote:

I use no digital devices in my reloading

Unless one is trying to set new bench rest standards reloading doesn't have to be this precise.

Even then it is mostly a waste of time.

Ted,
Your telling me you can't put the solid C par in the corner of your vise lightly to hold it with the vise corner??? I tried it both ways and get about the same read everytime?? sure you didn't misread me? holding a part in one hand and working a std. mic with the other gives me worse readings!

I started tech college in 1987

One of the first things you master is using micrometers

A one or two inch mic.....heck for that matter mics up to 6 or 8" are a one handed instruments

Almost 29 years later we have them up to 24" and use them all day and every day of the week......no digital mics.....no way

We do however have a 24" set of Mitutoyo digital calipers.....they are nice but cost as much as a used late model car

Clamp one in a vice if you want but if you are getting different readings on a 1" mic....a 24" would drive you insane

Using a micrometer accurately and fast is all about professional feel

Friction thimbles and ratchets are for put there for the others

If it's your tool use it however you want. ......I hear they are nice clamps also

Maybe vise is the wrong word. He more than likely meant stand. You've never used one? I have one, and only two hands.

Seen them? Yes....in catalogs

Use one? No....Never witnessed any toolmaker use one...ever!

I have absolutely no need for a micrometer stand but by all means you go right ahead

Like I stated before.....a micrometer is a one handed tool....not two

To the 'smiths and machinists who contribute here: I greatly appreciate your comments, learn a lot thereby, and have no reason cast aspersions on your parentage, experience, good will or character. That said, most of us here are amateurs, making ammo, not seals for rocket engines.

That said, we need to be cognizant of the level of accuracy needed for safety and good product. For us, that rarely goes beyond a couple of thousandths. If better is needed we can either up-grade our skills or go to a real expert.

Merry Christmas to All.