Inconsistant seating depth when loading 9mm?

Head stamp does make a difference.
It shouldn't, but it does.
CBC brass loads .010" longer than Blazer for one example. Same bullet, same comp die, both of my presses, happens every time.
Both brands weigh and measure the same, all I can figure is it must be something to do with the hardness of the CBC brass.
Check the head stamps on the long ones, see if there are any trends.

PO2Hammer said:

Head stamp does make a difference.
It shouldn't, but it does.
CBC brass loads .010" longer than Blazer for one example. Same bullet, same comp die, both of my presses, happens every time.
Both brands weigh and measure the same, all I can figure is it must be something to do with the hardness of the CBC brass.

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I've noticed this too. I also pulled some MXT brass (Shorter) off the range, and it has all kinds of problems, including this. Crooked seating about 5% of the time. I chucked them.

Maybe harder brass resists the bullet seating and is compressed slightly, then springs back a little from brass's elastic qualities.
Softer brass might resist less to seating pressure and not spring back.
That's my theory and I'm going down with it.

I would randomly take 25 bullets and measure the bullet OAL and see what you average and what deviations you have. That may explain the whole issue as some have already mentioned. You can also take a comparator kit and check the seating depth based on the ogive. If your ogive is seating at the same depth, then read the overall length and see what differences you get. As mentioned unless you use premium bullets then you will get variations, especially on plated bullets. My two cents.

LeftyTSGC

buba68 said:

Looking at the second picture where the OAL is longer it looks like the brass is slightly bulged where the crimp is and it might be just the angle of the picture or the light on the brass. Are you using a roll crimp or a taper crimp? If you are doing a roll crimp not a true roll crimp and you have inconsistent brass length it looks like the die is trying to crimp before the bullet is seated to the depth that you want. If that is the way you are crimping try backing the die up a little so it is not crimping so hard early in the seating process. Or you could try seating maybe 10 or so bullets without any crimp to see if your COL is consistent that way. You do not need much of a crimp just enough to take the flair off of the case mouth. A taper crimp die works well for 9mm. +/- a couple thousands is nothing to worry about on COL

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You nailed it!!!!
It's more than slightly bulged & you can clearly see the bullet's body & base.

This is extremely common with the generic/run of the mill reloading dies. Typical sizing dies size the heck out of the brass, it's nothing to size brass down 7/1000th's+. They want to makes sure they layer proof everything and the end result is gooder neck tension (+/- 5/1000ths) to hold them bullets in.

The issue is when you get a piece of thicker brass that is work hardened/sized too small and use the factory expanders that are just as bad at being not only undersized, they are typically too short and don't expand the brass deep enough. The end result is it takes excessive force to seat the bullet and this causes deflection, bullet deformation, case buckle, etc.

A factory 9mm expander next to a custom expander


Buy 1 of these lyman m-die expanders and it will take case of 90%+ of your oal issues.


Something to think about:
Neo bullet molds make custom expanders that use the lee universal expander die & typically their expander buttons are 4/1000th's under bullet diameter.

Myself the 1st thing I due when getting a new set of 9mm reloading dies is home/polish/open the sizing die 2/1000th's. The 2nd thing I do is toss the factory expander button and make a custom expander that has 2/1000th's neck tension on the thinnest brass I use (remington). Anymore I only use federal/blazer/ww brass, they are pretty consistent (+/ 1/1000th's) and the end result is +/- 3/1000th's neck tension.

There are 2 sides to neck tension & most reloaders want that gooder neck tension to hold the bullet in place. Well that comes at a price, namely it does nothing for accuracy and makes your reloading at the press inconsistent.

These are .358" bullets I load in the 9mm's


No wasp waist, no bulging of the case, no bullet base showing & just for the heck of it a +/- 3/1000th's crimp.

Showed this before, it's not hand/cherry picked by any means. It's nothing more then the test target used that day (green bullet pictured above) to test that load. I still use that load to this day for my short range 25yd or less blammo ammo/dirt clod killers.


Was plating around with that red bullet pictured above for a little while @ the 50yd line. That bullet is a design that came out in 1900 for the 38s&w. It is a hb version of that bullet. I made/tested several different hb pin designs And setted on this hb pin.


The black bull is 1 1/2"'s. The fliers are from 2 things:
Too light of a recoil spring in that 1911 (8#), wouldn't go back into battery consistent/lock up consistently. And some of the bases of the extremely long bullet were getting deformed (8/9bhn) by the web in the bottom of the case.

I've loaded 9mm's for a little while now, back in the 90's we'd fit 6" 9mm bbl's in our 1911 38super race guns and shoot countless 1000's of the lyman 358111 158gr lead rn bullets in them.

At the end of the day you're over sizing your brass too small. Then the expander isn't opening them large enough nor deep enough. The end result is oal's that are all over the place.

FWIW:
I set my 9mm dies up to use .358" cast bullets. If I want to use .355" factory jacketed bullets I use the same setup for sizing the brass, priming, expanding the brass and seating the bullet. I do not taper crimp on the last stage like I normally would with the cast bullets. Instead I use a lee factory crimp die. This sizes the brass down to factory specs and puts the correct amount of neck tension on that .355" bullet.

Berry's plated bullets use a very soft lead core. These are so soft if you drop them they will dent. So it's not uncommon to see rings on the bullet from the seating stem. The only way to minimize that is to use a custom seating stem that matches the contour of the bullet. Like the others have said brass of different hardness and wall thickness will have varying amount of force required to seat the bullet. Over crimping can and will buckle the brass even using a TC seating die. Crimping in a separate station will minimize this but you can still buckle the brass with too much crimp.

Jim K III said:

I'm using an older RCBS single-stage Rock Chucker press. I appreciate all the responses, tips, suggestions, and possibilities. I'll keep chugging away and I'm sure my reloading 'style' will smooth out and improve as I load more than a couple hundred rounds.

Click to expand...

As with most things---"Practice makes perfect".
Just go at a pace that's comfortable for you,
Soak up all the info that you can,
And, MOST IMPORTANTLY, be safe and HAVE FUN...!!!
When it becomes a chore, it's not worth doing anymore...

frogfurr said:

Mixed brass shouldn't make a difference.

Click to expand...

It does. If seating and crimping in the same step it will effect the amount pressure on the bullet nose, and this can effect the COL of the cartridge. Have you ever noticed a difference in sizing and seating resistance with various brass?

Jim K III said:

After seating 5 bullets I check each one with a caliper. Most seat depths are ~1.155 + or - a thousand or two. However, every once and a while one will seat @ ~1.165. See pics. I check for grit in the shell holder

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Any debris in the shell holder, under the case, isn’t going to make the seating depth less.

Jim K III said:

I would think the only factor involved is the seating plug itself.

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There are lots of things than can effect OAL. As you can read from the pages above, you will also note more than a few of them couldn’t be the issue with your single stage press.

Instead of list every possibility, it might be better to keep things simple and start at the beginning and that’s the bullet.

Grab a handful and measure them. It’s not unheard of for them to be different. Like these SMK’s.



So if I seated those two bullets to the exact same depth, I would have a .005” difference in OAL.

However if I do not use the tip and measure off a datum on the ogive, I get the exact same measurement with both, regardless of the fact the tip differs by .005”



If you don’t have anything you can use to measure like that, remove the seating insert from your die and use it to measure your 1.155 & 1.165 OAL rounds again, like this.



Knowing the results from this test will tell us more than all the guessing in the world could.

All that said, .010 difference in seating depth, if you actually have that problem, isn’t going to show up on target at common pistol ranges with most pistols and users. If you are looking for accuracy above that level, you shouldn’t be using plated bullets anyway.

[QUOTE="jmorris, post: 11946185, member:

View attachment 1001164

If you don’t have anything you can use to measure like that, remove the seating insert from your die and use it to measure your 1.155 & 1.165 OAL rounds again, like this.

View attachment 1001165

Knowing the results from this test will tell us more than all the guessing in the world could.
.[/QUOTE]

This is a great idea.

jmorris said:

Any debris in the shell holder, under the case, isn’t going to make the seating depth less.



There are lots of things than can effect OAL. As you can read from the pages above, you will also note more than a few of them couldn’t be the issue with your single stage press.

Instead of list every possibility, it might be better to keep things simple and start at the beginning and that’s the bullet.

Grab a handful and measure them. It’s not unheard of for them to be different. Like these SMK’s.

View attachment 1001162 View attachment 1001163

So if I seated those two bullets to the exact same depth, I would have a .005” difference in OAL.

However if I do not use the tip and measure off a datum on the ogive, I get the exact same measurement with both, regardless of the fact the tip differs by .005”

View attachment 1001164

If you don’t have anything you can use to measure like that, remove the seating insert from your die and use it to measure your 1.155 & 1.165 OAL rounds again, like this.

View attachment 1001165

Knowing the results from this test will tell us more than all the guessing in the world could.

All that said, .010 difference in seating depth, if you actually have that problem, isn’t going to show up on target at common pistol ranges with most pistols and users. If you are looking for accuracy above that level, you shouldn’t be using plated bullets anyway.

Click to expand...

Quality post/advice!

I only reload 1 round that I go to this degree of accuracy of measurement, and I only reload pistol rounds, anyway.
When I started reloading .22TCM I had trouble with OAL in that tiny caliber— enter a custom case trimmer and headspace gauge which allowed me to set up my dies properly. The gauge allows me to measure the shoulder from a datum point on the shoulder of the cartridge. Once my cartridges were “uniform” the OAL variance went away.
In the op’s situation, @jmorris has suggested the correct solution for accurate measurements of COAL in 9mm and should yield “some” improvement.
With bullet uniformity being what it is for those projectiles, improvement will be minimal. I don’t think you’ll see enough improvement to warrant your time spent chasing down the additional few thousandths of consistency for plinking ammo.
Your current process seems sound.