Case shrinkage vs Headspace

[Hans Gruber]

Hey guys,

Yes, me again.

So I was going through the brass that I shot over the weekend and I noticed that my cases are shrinking precipitously. I looked over my sizing die and determined that I probably wasn't actually FL sizing due to my following the Redding instructions and backing out the die quite a bit. I was most likely just neck sizing essentially because the shoulder never hit the top of the die.

My headspace on these cases was teetering on no-go too short. Through my research for .308 Win I found the range 1.627-1.633 as an appropriate range to test for in my headspace gauge. Most of my cases were right at the 1.627 mark. My lengths have gone from their trimmed length of 2.005 down to 2.001 on average with a couple under 2.000.

So, I screw down my sizing die. Run some of my Remington .308 testers through it (20 cases that I use to test tools and dies on) to my satisfaction.

I run the 4 shortest of my shooting brass through it after adjustments. I'm going to cull these cases regardless most likely so let's see what happens!

The case lengths happily grew from 1.996-98 up to 2.001-2.003. I can live with that, but my headspace # tanked to 1.620-1.623, firmly in NOGO.

So... how to I straighten out the case without bumping the shoulder back into boomland? Do I just need to back out the die a smidge or can I not straighten the case without hitting the shoulder? Is this lot of brass toast?

Still trying to learn, thanks for any advice offered.

[ar15barrels]

You should be bumping the shoulder about 0.002" for reliable function.
This will cause some case length growth as you are squeezing down the body of the case and the extra is extruding out the front of the case.
You will also see shrinkage after firing as that brass pulls back down into the expanded case.

Measure your cases after sizing to determine if they need trimming.
Measuring before sizing is just going to confuse you until you fully understand what happens to the brass through each cycle of it's life.

[Hans Gruber]

I guess my question is, if I bump the shoulder .002, what exactly does that do to my headspace? My understanding is that the .002 bump would reduce my headspace by that amount, thereby running my brass below the 1.627 minimum. Should I not be concerned? Is it possible that this is just how brass forms in my rifle due to short headspace in this particular rifle?

[ar15barrels]

Don't be concerned about absolute measurements.
Headspace is a RELATIVE measurement that takes the cartridge case and the barrel/bolt relationships all into account.

Forget all about 1.6xx numbers.
Only deal in knowing what a fired case measures and adjusting the die so that your new loaded ammo is 0.002" shorter in shoulder length so that it fits back into the chamber with minimal headspace.
Your fired case measurment is a very good indicator of the barrel/bolt's chamber length.

Those absolute 1.6xx numbers are derived from headspace gauges.
Headspace gauges are used to inspect a gun to see if it's within "industry standards".
Industry standards don't matter in custom ammo because the ammo is intended for a specific gun.
It's completely acceptable to make ammo that's 0.015" longer or shorter than "spec" if that's what the gun needs.
The "spec" only applies to factory ammo and guns.
Handloading allows you to throw ALL those specs out the door and forget about them forever if you understand what you are doing and more importantly WHY you are doing it.

[swerv512]

does that mean that so long as i full length size, that i dont have to worry about headspace???

[ar15barrels]

does that mean that so long as i full length size, that i dont have to worry about headspace???

oh no.
It's quite possible to have excessive headspace caused by full length sizing.
You need to learn how to adjust the sizing die to size ONLY enough.
If the die is all the way down hard against the shellholder, it's quite possible you are creating excessive headspace.

[swerv512]

i always come up one full turn after hitting the die when i FL size. that's what i read in the RCBS die manual. how do i even measure headspace?

[ar15barrels]

i always come up one full turn after hitting the die when i FL size. that's what i read in the RCBS die manual. how do i even measure headspace?

http://www.realguns.com/archives/035.htm

You are not full length sizing if you have un-screwed the die 0.071" (one full turn) after it touches the shellholder.

[Seesm]

I am Sooooo LOST on re-loading.... I hope I do not hurt myself...

[swerv512]

http://www.realguns.com/archives/035.htmYou are not full length sizing if you have un-screwed the die 0.071" (one full turn) after it touches the shellholder.

oops! my mistake- i was thinking of the seating die.
must be getting late...

back to headspace- if i indeed follow the usual "touch the die to the shell holder base and then screw the die DOWN an additional 1/8 to 1/4 turn," do i need to worry about headspace?

thanks for all the info AR.

[Hans Gruber]

Don't be concerned about absolute measurements.
Headspace is a RELATIVE measurement that takes the cartridge case and the barrel/bolt relationships all into account.

Forget all about 1.6xx numbers.
Only deal in knowing what a fired case measures and adjusting the die so that your new loaded ammo is 0.002" shorter in shoulder length so that it fits back into the chamber with minimal headspace.
Your fired case measurment is a very good indicator of the barrel/bolt's chamber length.

Those absolute 1.6xx numbers are derived from headspace gauges.
Headspace gauges are used to inspect a gun to see if it's within "industry standards".
Industry standards don't matter in custom ammo because the ammo is intended for a specific gun.
It's completely acceptable to make ammo that's 0.015" longer or shorter than "spec" if that's what the gun needs.
The "spec" only applies to factory ammo and guns.
Handloading allows you to throw ALL those specs out the door and forget about them forever if you understand what you are doing and more importantly WHY you are doing it.

Sweet, you just made it click for me I think. My conclusions based on my new understanding:

• My chamber appears to be about 1.627" since that's the headspace # that it seems that all of my brass comes out at (several brands).
  
• I should back out the sizing die and run a piece of brass through, moving the die down in tiny increments, until the brass comes out at 1.625" headspace. This tells me that I've bumped the shoulder .002".
  
• Loading brass at "under min headspace" is ok IN THIS RIFLE due to its smaller chamber.
  
• My smaller chamber may explain why I saw pressure signs on some factory ammo.
  
• Listen to my brass and what it's trying to tell me about my rifle.

I guess that this is where we start getting into the "art" of reloading eh?

Thanks!

[ar15barrels]

My conclusions based on my new understanding:

• My chamber appears to be about 1.627" since that's the headspace # that it seems that all of my brass comes out at (several brands).
  
• I should back out the sizing die and run a piece of brass through, moving the die down in tiny increments, until the brass comes out at 1.625" headspace. This tells me that I've bumped the shoulder .002".
  
• Loading brass at "under min headspace" is ok IN THIS RIFLE due to its smaller chamber.
  
• My smaller chamber may explain why I saw pressure signs on some factory ammo.
  
• Listen to my brass and what it's trying to tell me about my rifle.

I guess that this is where we start getting into the "art" of reloading eh?

YES!

[ar15barrels]

if i indeed follow the usual "touch the die to the shell holder base and then screw the die DOWN an additional 1/8 to 1/4 turn," do i need to worry about headspace?

Blindly following that advice will sometimes create excessive headspace.
Without proper case gauging equipment, you will never know when that's happening.

[rksimple]

Sweet, you just made it click for me I think. My conclusions based on my new understanding:

• My chamber appears to be about 1.627" since that's the headspace # that it seems that all of my brass comes out at (several brands).
  
• I should back out the sizing die and run a piece of brass through, moving the die down in tiny increments, until the brass comes out at 1.625" headspace. This tells me that I've bumped the shoulder .002".
  
• Loading brass at "under min headspace" is ok IN THIS RIFLE due to its smaller chamber.
  
• My smaller chamber may explain why I saw pressure signs on some factory ammo.
  
• Listen to my brass and what it's trying to tell me about my rifle.

I guess that this is where we start getting into the "art" of reloading eh?

Thanks!

Feels good to finally get it huh? Now you are leaps and bounds ahead of 90% of reloaders out there who don't have a clue about this concept.

[Hans Gruber]

Feels good to finally get it huh? Now you are leaps and bounds ahead of 90% of reloaders out there who don't have a clue about this concept.

If feels really good considering the amount of measuring, sorting, die tweaks and head scratching I did yesterday. I was afraid that I was going to have to dump all of my brass and start over, probably missing the CPRS shoot next weekend.