Bullet Diameters -- Micrometer measurements

[IDescribe]

This post is definitely a "for your curiosity" sort of post. It started with my recent Precision Delta purchase with 9mm .355 124 JHP and the 38 Super .356 124 RN with the purpose of evaluating a .356 jacketed against a .355 jacketed, AND with the purpose of evaluating the supposedly slightly over-sized PD .355 124 JHP vs the supposedly undersized Montana Gold .355 124 JHP.

I have yet to load a single live round with those Precision Deltas, but in my initial measurements of the bullets using calipers, the PD ".356" generally came in at .356 , and the PD .355 generally came in at .355.

After commenting that I might by a mic to get more accurate readings, a buddy with a bunch of mics offered to sell me a couple. I bought two Brown & Sharpe micrometers. The relevant one here is a 0-1 that measures to 1/10,000, has a slip thimble, and with which my measurements are very much repeatable.

I added more bullets to the mix than just the Precision Delta and Montana Gold. Below are measurements to the ten thousandth for ten bullets each of seven different make/models, :

PD .356 124gr RN -- 1 @ .3560 | 1 @ .3561 | 3 @ .3562 | 5 @ .3563

PD .355 124gr JHP -- 2 @ .3550 | 6 @ .3551 | 2 @ .3552

MG .355 124gr JHP -- 1 @ .3551 | 1 @ .3552 | 7 @ .3553 | 1 @ .3554

SNS .356 135gr RN -- 1 @ .3559 | 3 @.3560 | 5 @ .3561 | 1 @ .3562

ACME.356 147gr FP -- 7 @ .3561 | 3 @ .3562

Bayou .356 124 TCG - 1 @ .3565 | 2 @ .3568 | 5@ .3569 | 1 @ .3571 | 1 @ .3572

Blue .355 125gr RN -- 4 @ .3555 | 6 @ .3556

I know ten samples per bullet is not definitive. The mic was calibrated before taking these measurements, so I suspect the accuracy is good if not spot on, the precision is excellent, and even if accuracy is a hair off, the numbers relative to one another are good.

What did I learn?

It would appear that:

• ACME and Blue Bullets are producing bullets that are at least as consistent and probably more consistent in terms of diameter than PD's and MG's 9mm jacketed.
• The lot of Precision Delta .355 124gr JHP that my recent order came from does not appear to be "over-sized" in any way and in fact seems to be 1-2/10,000 smaller than the equivalent Montana Gold.

That about it. I don't want to make too much of this little test. I would caution anyone from making any assumptions regarding consistency in diameter as I measured it being tied directly to accuracy/precision of the bullets in actual use. The Bayou 124gr TCG above has a range of .0008, twice as big as the next biggest range, yet that particular Bayou bullet has been extremely accurate with a couple of different powders in all of my 9mm pistols. Every pistol seems to like it. The Blue Bullets 125RN, on the other hand, has a diameter range of .0002, and while accuracy has been excellent in my VP9 and Glock 17, the Blue 125 (and Blue 147, for that matter) have been subpar in my CZs, bested by every other make of coated bullet I've tried. Super consistent diameter does not automatically equal tiny groups on paper.

So, again, this is a "for your curiosity" sort of a thread. Take it for that. And talk amongst yourselves.

One of these days, I'm going to load those Precision Deltas and see if they shoot.

[Sarge]

Hair splitting 101.

[GrumpyOne]

Hair splitting 101.

Maybe.....but he can measure that split hair with that micrometer...

All in all, it's not bad info to gather, if you are looking for the most consistent bullets...

[IDescribe]

Hair splitting 101.

Absolutely agreed. That's why I cautioned anyone against assuming the results would translate to anything meaningful.

For me, I had read in another thread here that Precision Delta 9mm were a bit oversized, and that MG were typically smaller than PD. I wanted to know, my calipers can't measure to a resolution that would tell me, and I'd had enough occasions previously where I wished I had a mic that I decided to buy one. For the record, it's used. I got a great deal in it.

Again, no one should make much of this. It was for curiosity's sake.

[Tino2212]

Hair splitting 101.

Maybe.....but he can measure that split hair with that micrometer...

...

If he knows how to use it yes he can , micrometers are extreamely temperature sensitive .

If you don't hold it the right way you can flush your measurements down the drain .

[9x45]

Hair splitting 101.

Maybe.....but he can measure that split hair with that micrometer...

...

If he knows how to use it yes he can , micrometers are extreamely temperature sensitive .

If you don't hold it the right way you can flush your measurements down the drain .

Problem being is that human hair varies between 0.00067" to 0.00709", ( 7 tenths to 7 thousands) ie, measured to 1/100,000" but typically expressed in microns as measured by a scanning electron microscope. A typical barrel micrometer is indicated by .0001", ie, tenths. There is no requirement to correct for temperature because the linear co-efficient of expansion for lead is 15 x (10^-6 inch/inch degrees Rankine). tR=t(Fahrenheit) + 460. However the ability to correctly read the the tenths barrel on the micrometer is necessary for accurate measurements along with a calibration to a 1" gage block and a good 0-1 barrel micrometer. Also with coated bullets you want to measure at 3 locations to include the variation in coating. Brown and Sharpe are good quality micrometers. Most shooters don't own micrometers so when they decide to measure bullet diameter they tend to attach a significance to the variations of a few tenths. What would be a more interesting measurement would be to correlate bullet diameter variation to accuracy variation at a meaningful distance.

Bayous as measured on a Starrett 0-1

Edited May 11, 2016 by 9x45

[Sarge]

Egads!!

[Sarge]

Hair splitting 101.

Absolutely agreed. That's why I cautioned anyone against assuming the results would translate to anything meaningful.

For me, I had read in another thread here that Precision Delta 9mm were a bit oversized, and that MG were typically smaller than PD. I wanted to know, my calipers can't measure to a resolution that would tell me, and I'd had enough occasions previously where I wished I had a mic that I decided to buy one. For the record, it's used. I got a great deal in it.

Again, no one should make much of this. It was for curiosity's sake.

I know. I also know some bullets are accurate in my guns and some are not. Funny thing is the fattest ones are by far the least accurate.

[ChemistShooter]

Good solid info. This work needed doing. It would've been a shock to find a lot of variation.

A random comment: As a wild guess, I would think uniformity would affect accuracy more than bullet diameter. How closely the bullet conforms to the ideal bullet shape.

[9x45]

Egads!!

13 years as a tool and die machinist followed by 33 years as a mechanical engineer, that's just how things come out.

Chem, this would be a great project for you! A study in not only bullet tolerance variation, but a correlation of average diameter to accuracy in you gun, and a study of concentricity effects on accuracy, hours and hours of data logging....

[Youngeyes]

The new math. Simple. Time to put away the micrometer.

+ + =

[9x45]

The new math. Simple.

Yup, the only thing that matters is what happens after the beep!

Edited May 11, 2016 by 9x45

[shred]

We've had to measure a lot of bullets with micrometers (calibrated .00005" Mitutoyos mostly) as part of the case-gauge business.

All pistol bullets vary when measured at multiple points. Some more than others. Plated, coated and lead bullets generally have the most variation.

They occasionally exceed the supposed diameter by a thou to three in he worst case if they've been dinged up depending where you measure. A friend in the casting business says lead alloys change size slowly after casting as well so there's some extra small variation from how long it was between casting to coating & sizing.

Concentricty of brass and bullet is generally much worse than any bullet size variation.

But, the slide closes with something like 15Gs of force and then 30K PSI cramming the bullet down the barrel does a pretty good job swaging out any remaining differences.

[ChemistShooter]

And waddya know, a Caldwell Premium Chrono and a thousand 115 gr Bayou Bullets both landed on my doorstep today.

Don't tempt me.

[9x45]

But, the slide closes with something like 15Gs of force and then 30K PSI cramming the bullet down the barrel does a pretty good job swaging out any remaining differences.

Yup the ultimate high speed swager at about 45,000 G's for a 9mm. I'd like to have a $500 digital mike, but for now I'll continue using my 46 year old Starrett.

[9x45]

Don't tempt me.

Go for it! You need that $500 digital mike for the experiment.....Now you can record out to 5 decimal places, awesome, well except your last digit will only record a zero or a 5. Don't breathe on it while you measure....

Edited May 11, 2016 by 9x45

[shred]

The hotness at the last trade show I was at is the non-contact laser systems. Super cool, they can give you a complete profile or even 3D mesh down to some multiple of the wavelength of the light they use. Also super expensive.