Why is my 308 brass shrinking??

[Brianma65]

I have some Sako and RP brass that is 3 times fired.
I trimmed it all to 2.005,last time out. After FL resizing, most of it measures,1.990 to 2.000.
With a few measuring at 2.005.
About 90 pieces.
These were used for load development, with various powder charges.

Should I toss the short ones? Or just continue on?

 

[cosmic]

Sounds like you are trimming before sizing... trim after sizing and life will be good. You can use the shorter brass.

 

[Brianma65]

Sounds like you are trimming before sizing... trim after sizing and life will be good. You can use the shorter brass.

Not doing that.
I trimmed all the Sako brass, to 2.005, last week. FA case trimmer. Ran them through the SS cleaner for an hr, resized, then ran them through the FA SS tumblr for 3 hrs. Then I trimmed to 2.005.
Fired them all, then resized last night. Just measured and 90% are under 2.000.
That’s it. Haven’t trimmed them yet.

Are the SS pins beating them down?

I noticed before, when I used to trim ,chamfer and debur, that the chamfered edge ,would be removed ,after SS tumbling.

(I used to run them through the tumbler, to remove any brass shavings that may have been left behind)

Anyway, glad I can use the shorter brass. It’s all I’ve got left

 

[Cameron SS]

So possibly dumb question but just want to rule out the obvious.

Did you measure the cases immediately after trimming to confirm the intended dimension?

 

[Brianma65]

So possibly dumb question but just want to rule out the obvious.

Did you measure the cases immediately after trimming to confirm the intended dimension?

Yes, I measured all my brass , the last time I trimmed them. All brass was 2.005.

I haven’t trimmed this batch yet,as they just come out of the dryer.
So far they’ve been SS tumbled for one hr,resized,tumbled for 3 hrs.
That’s it.

Here’s a pic of my brass before sizing . And after.

Is it normal for my brass to be that short after firing? They were all trimmed to 2.005.

Are my caliber pooched?

 

[Brianma65]

So possibly dumb question but just want to rule out the obvious.

Did you measure the cases immediately after trimming to confirm the intended dimension?

Yes, I measured all my brass , the last time I trimmed them. All brass was 2.005.

I haven’t trimmed this batch yet,as they just come out of the dryer.
So far they’ve been SS tumbled for one hr,resized,tumbled for 3 hrs.
That’s it.

The first pic is an unsized piece, second piece is sized.
Is it normal for my brass to shrink after firing?
This brass was trimmed to 2.005. Then shot.
It’s now shorter?

 

[rick357]

Sounds like your chamfering process is too aggressive and when you tumble afterwards in the steel it takes that soft sharp edge off. Chamfering is meant to clean the edge of the mouth and to put an incredibly slight bevel on the 12 thou or so thick brass, not to sharpen it.

Forgot to add, three hours (3?!?) in the ball mill? Why, when they have already been in there for an hour?

 

[Brianma65]

Sounds like your chamfering process is too aggressive and when you tumble afterwards in the steel it takes that soft sharp edge off. Chamfering is meant to clean the edge of the mouth and to put an incredibly slight bevel on the 12 thou or so thick brass, not to sharpen it.

Forgot to add, three hours (3?!?) in the ball mill? Why, when they have already been in there for an hour?

I can see your point ,on why the bevel is being removed. I’ll cut back on the timer and not chamfer as much.

But that still doesn’t explain why these have shrunk.
And these were chamfered after all cleaning was done.
And measured at 2.005.

The pic is of the same case. Fired and unsized ,then resized.

 

[Kratos]

I can see your point ,on why the bevel is being removed. I’ll cut back on the timer and not chamfer as much.

But that still doesn’t explain why these have shrunk.
And these were chamfered after all cleaning was done.
And measured at 2.005.

The pic is of the same case. Fired and unsized ,then resized.

Maybe your calipers were out of zero when you had initially measured the 2.005”?

I used to work with digital calipers every day when I was in hydraulic mechanics, and I bought budget ones. The machinist showed me how my calipers can slip and be out by up to a quarter inch. He had expensive ones (can’t remember the brand) and demonstrated how they never slip. I now run mechanical (analog) calipers because they are way less likely to slip. I’m not saying this is your issue, but something to consider.

 

[Scarheart]

Not doing that.
I trimmed all the Sako brass, to 2.005, last week. FA case trimmer. Ran them through the SS cleaner for an hr, resized, then ran them through the FA SS tumblr for 3 hrs. Then I trimmed to 2.005.
Fired them all, then resized last night. Just measured and 90% are under 2.000.
That’s it. Haven’t trimmed them yet.

Are the SS pins beating them down?

I noticed before, when I used to trim ,chamfer and debur, that the chamfered edge ,would be removed ,after SS tumbling.

(I used to run them through the tumbler, to remove any brass shavings that may have been left behind)

Anyway, glad I can use the shorter brass. It’s all I’ve got left

You just said you trimmed then resized! Exactly what Cosmic asked you.

 

[Kratos]

You just said you trimmed then resized! Exactly what Cosmic asked you.

He bought brass.
Trimmed. Measured.
Cleaned.
Sized.
Cleaned.
Trimmed. Measured.
Fired.
Sized. Measured. This is where they are short.

After firing he hasn’t trimmed them. And before firing trimming doesn’t matter if he measured them at the 2.005” he stated.

 

[Brianma65]

You just said you trimmed then resized! Exactly what Cosmic asked you.

Yes sorry, that was a typing mistake.
I never trim first.
I’m 100% certain.

 

[Brianma65]

Ok let me start over .. lol
I shot the factory Sako ammo.
resized all the brass .
tumbled
Trimmed to 2.005
Chamfered/ debured
Loaded
Shot.

Now I just did the same process, and 90% of my brass are under 2.000

 

[Brianma65]

He bought brass.
Trimmed. Measured.
Cleaned.
Sized.
Cleaned.
Trimmed. Measured.
Fired.
Sized. Measured. This is where they are short.

After firing he hasn’t trimmed them. And before firing trimming doesn’t matter if he measured them at the 2.005” he stated.

Lol, got me there

 

[Brianma65]

Anyway, I’m gonna load them up.
They’re for hunting anyway.

Also, I just went and got my mitoyo calipers back ,from loan.
I’ll check with those as well.

 

[Brianma65]

You just said you trimmed then resized! Exactly what Cosmic asked you.

I should have used a paragraph.
I meant ,that’s what I started with. (2.005)

 

[bigedp51]

Below on the left is a case that was full length resized, trimmed and fired again. The case was then tumbled too long and the case mouth was peened. Before tumbling the case mouth was still flat with slightly beveled edges. The case on the right is a brand new unfired case right from the Winchester bag after a factory tumbling for comparison.

Admittedly I left the case on the left in my wet tumbler too long and the stainless steel media and the cases hitting each other peened the case mouth.

Take a magnifying glass and examine your case mouths after tumbling, if you can not see evidence of case mouth trimming you are tumbling too long.

Bottom line, wet tumbling can make the cases shorter and ruin a case trimming by pounding the heck out of the case mouth.

 

[Brianma65]

Ya, I’ve learned not to tumble ,after chamfering/ deburring.

I understand that my cases will shrink a little,after firing.
Because the sides are expanding, to form to my chamber.

But shouldn’t they grow longer from FL sizing?

Well,longer than .002, anyway.

 

[rick357]

Ya, I’ve learned not to tumble ,after chamfering/ deburring.

I understand that my cases will shrink a little,after firing.
Because the sides are expanding, to form to my chamber.

But shouldn’t they grow longer from FL sizing?

Well,longer than .002, anyway.

Not really. Just how much are the walls being squeezed during full length resizing, way less than a thou. As well, you are bumping the shoulder back when full length resizing and if your die is set up properly, it is only bumping that shoulder back a thou or two at most so that brass is moved back into the body portion as well. So, the only stretching that is occurring is in the neck and a couple of thou is quite a bit if you think about how long that neck isn't - and yes I meant to type it like that.

 

[bigedp51]

Ya, I’ve learned not to tumble ,after chamfering/ deburring.

I understand that my cases will shrink a little,after firing.
Because the sides are expanding, to form to my chamber.

But shouldn’t they grow longer from FL sizing?

Well,longer than .002, anyway.

I size my .223/5.56 cases with a small base die for three different AR15 rifles, and this reduces the case diameter more than a standard die. And the small base die will cause the case to "grow" more after sizing than a standard die.

But chambers and dies vary in size and a fat chamber and a skinny die will cause more case growth. And on the flip side if you have a skinny chamber and a fat die you will have little to no case growth.

You can check this by measuring a fired case at three points along the case body and then remeasure after full length resizing at the same points.

Example about full length dies, I have a standard .223 Lee full length die that will reduce the case diameter "more" than my RCBS small base die.

I started wet tumbling after I got my first AR15 and the cases were scratching my dies and brass. And wet tumbling would scrub all the embedded dirt and grit from the cases that hit the ground. And then trim the cases with a WFT trimmer and remove any damage to the case mouth.

Last year I replaced my old Midway vibratory tumbler with a Lyman Turbo 1200 Pro and started using untreated lizard litter and Nu Finish car polish. And my point being I can leave the cases tumble all night in a vibratory type tumbler and not peen or damage the cases.