9mm OAL caliper measurement differences.

[gonoles_1980]

I suspect it's because I have a cheap digital caliper. But it could be my Lee Seating Die doesn't seat the same distance each time.

I initially set an OAL of 1.080", when I measure my bullets, the length varies from 1.0775 to 1.0830.

Is that really a big enough difference to affect performance.

 

[judgedelta]

It's not necessarily your caliper. Mine does the same with Lee dies. Should make no difference as long as you aren't seating on the lands. Plunk several of the long ones.

I even sent a bullet off and had a custom seater made. Made no difference.

 

[Jim Watson]

Only .0055" spread, that's not bad.
The bullet noses vary, brass thickness/resistance to seating/flex in press varies, OAL varies.
Unless you are shooting NRA or ISU bullseye with precision slow fire at 50 yards, it isn't going to matter. If you ARE shooting 50 yard slowfire and are not getting good accuracy, you need matched brass and premium bullets.

 

[X-Ring]

Your calipers and dies are most likely just fine. Bullets vary some, thus I have never found a seating die that will perfectly seat all bullets all the time. You will not even notice a 0.006 variation. If I were seating to 1.080 I would adjust depth to be between 1.080 and 1.090. The closer to 1.080 the better, but not under.

 

[mdi]

Bullet lengths will vary as much as .005" depending on the type and quality of the bullets. I have some "Match Quality" bullets that vary by .003" in length (which ain't nuttin' really!)...

 

[ku4hx]

I'd take .0055" (55 parts in 10,000) any day of the week. Generally, so long as I'm not bumping the rifling, my acceptable COAL variance is .005" ... 5 parts in 1,000.

Whether or not a particular COAL effects accuracy/performance can be a highly gun-specific proposition. For the CZ75Bs I'm familiar with, a COAL over 1.055" touches the rifling with some bullets and has a significant impact on the gun consistently going fully into battery. Apparently these guns have a very short leade. Your gun will tell you what it likes or doesn't like.

 

[Walkalong]

That 1.0775 on the digital caliper is rounded up, or down, who knows which, but, as posted a .005 or .006 spread is acceptable and not uncommon. Getting a spread below .005 happens with a great bullet to seater stem fit and only seating going on, but .005, or a bit more, is common.

 

[GJSchulze]

I wish my spread was only .005. Mine can vary from 1.12 to 1.14 (147 gr FMJ-TC). And guess what? I've stopped worrying about it. Most measure from 1.13 to 1.14. Unless you're at max charge there's no safety issue. Your velocity will vary, but this is 9mm handgun. The difference in accuracy because of OAL is far less than your own ability, most likely.

Your caliper will always read 0 or 5 in the 10,000th place and if you think you can measure that finely, think again.

I sort by headstamp and I often have to adjust my seating die when I change HS. If you don't sort then the difference in brass accounts for the spread as Jim W said. I'm surprised you don't get more spread than that.

Even with a wide spread only a few percent will be that bad. Most of mine are between 1.133 and 1.138. You're likely getting a Gaussian or similar distribution.

 

[gamestalker]

No biggie, just don't let it get over .010" and you'll be fine.

Bullet olgive inconsistencies alone can account for a lot of that variance, not at all unusual. I see it also, I've just learned to accept it as the norm, cause it is.

GS

 

[gonoles_1980]

Thanks guys. Another one of my ACDisms when reloading.

 

[CZ9shooter]

I notice OAL differences when dealing with mixed brass. The tighter cases would tend to be longer than the weaker ones. Just a few thousands like the OP describes, so no big deal really. Sorting brass and using a seater plug that matches bullet profile keeps variation to a minimum. But either way, me nor my guns can tell any difference.

 

[digid]

You did not say what press you are using. In my Dillon 550B which is a 4 station progressive I find it changes a bit if I do not have a cartridge in all 4 of the stations. Especially the sizing station which is directly across from the seating die. . I also changed my set up so that the bullet seating die only seats, and added a Lee factory crimp in station 4 and noticed much more consistency. But as others have stated the numbers you are getting are acceptable.

 

[rfwobbly]

Your tolerance of +/-.003 looks great.
Measure a box of factory rounds some time and you'll freak out.

 

[Bart B.]

I hope nobody thinks that a .0055" spread in 9mm cartridge length is the same dimensional spread their bullets will have to the rifling when fired. Their case head is not against the breech face when they're fired. The "head clearance" the case heads have to the breech face won't be the same spread as the cartridge overall lengths have. It's possible the round with the shortest OAL will have its bullet closest to the rifling when fired. If all rounds OAL's are the same, both head clearance and bullet to rifling will have a small spread of a few thousandths.

This is why OAL length measurements of rimless straight and bottleneck cases is usually good for only magazine length issues.

 

[Walkalong]

I hope nobody thinks that a .0055" spread in 9mm cartridge length is the same dimensional spread their bullets will have to the rifling when fired.

He's just wondering if that kind of spread is OK/normal, and if his equipment is doing alright. A natural question for folks when they first start measuring ammo they make. They read post after post mentioning OAL's, without mention of a variance, and then they question theirs when it isn't always the same. A pretty natural question that we get a lot.

9MM bullet jump to the rifling is a whole nother question. Maybe you should start a thread about it. Might be an interesting discussion.

 

[Bart B.]

OK, here it is:

http://www.thehighroad.org/showthread.php?p=10019055#post10019055

 

[jmorris]

Also remember your seater might not touch the tip of the bullet and be seating by some point on the ogive. Meaning you will need something like this to measure the difference. http://www.midwayusa.com/product/23...ad-bullet-comparator-basic-set-with-6-inserts

What bullet are you using? Do you have a photo of the top of the bullet in a loaded round? Do you have the correct seater installed in the die?

Or if you can suppress your OCD, just shoot them.

 

[Walkalong]

OK, here it is:

Outstanding!

 

[Bart B.]

You can also use a 39 cent nylon spacer with your calipers. Here's one with a 3/8ths inch inside diameter being used on a .30-06 case used in setting up a FL die to set the fired case shoulder back a few thousandths:

 

[Walkalong]

I made some out of SS. Folks have come up with all sorts of clever ways to do it.

For .35 Remington

For .308