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I ask the following with some trepidation .....................

Please can someone explain why my .308 cases lose length after firing?

You will see from my previous threads that I am a relative learner to precision reloading. However, my approach to the matter has been logical and thorough.

The below-mentioned was performed on donated once-fired (by A-Another person) FC cases:-

After de-capping and cleaning, I full length resized.

I then trimmed to 2.005. Brass was definitely trimmed evidenced by the swarf produced. I repeatedly checked the length>

This process was performed after the second firing. I am sure that the cases were 2.005 for the 3 firing.

Today, I prepared 22, 3 times fired cases. When I checked them, most of the were 2.002, some were 1.997!!!!

I HAVE NOT ALTERED MY TRIMMER! (Please believe me)

What is causing my cases to shrink? (I can get Viagra for another shrinking problem :oops: but can anyone give a reason for this problem?

Many thanks in advance.

Cam
 
I'm confused. Are they shorter AFTER you resize them? What is their length when removed from the chamber?
 
I'm confused. Are they shorter AFTER you resize them? What is their length when removed from the chamber?

Many thanks for your reply.

They are shorter after I have shot them, AND, after F/L sizing, they are still less in length than the 2.005 they were prior to firing.

Many thanks

Cam
 
Ok, we have that info. Need to know make and type of rifle, I'm guessing it's an AR. Make of dies and press? Do you get the same results with new brass? Aside from that, cutting .010 shorter than spec is not something I'd do.
 
Ok, we have that info. Need to know make and type of rifle, I'm guessing it's an AR. Make of dies and press? Do you get the same results with new brass? Aside from that, cutting .010 shorter than spec is not something I'd do.

The rifle is my first rifle: it is a Parker Hale 1200 TX (A bolt-action 7.62mm, 1980's sniper rifle) I use it to compete at my club in FT/R.

I Use a Redding S-Line F/L Bushing die. I use aforesaid die in and RCBS Rockchucker Supreme press.
 
silly question did you make sure your calipers are zeroed when you measured?
 
ok next question what is your load data, suspect dkhunt14 is correct if you're using a light load then the forming might not be taking place fully until a couple of firings granted the brass might also be work hardened as well. i wouldn't worry too much its a 308 win i shot that for a number of years very forgiving cartridge.

if they are donated cases i truly do suspect your cases are taking a couple of firings to form to your chamber. Thats why either start with virgin brass, or anneal the case then shoot it.
 
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Your 7.62 x 51 chamber is more generous than your .308 Winchester sizing die, so the case has expanded lengthwise to the shoulder which displaced brass has caused the case to shrink in overall length.

Read this: http://www.303british.com/id36.html

Lesson:

  • Don't trim brass for a military chamber until you've fired them at least once.
  • Only size cases for this chamber until they j-u-s-t chamber without effort
 
ok next question what is your load data, suspect dkhunt14 is correct if you're using a light load then the forming might not be taking place fully until a couple of firings granted the brass might also be work hardened as well. i wouldn't worry too much its a 308 win i shot that for a number of years very forgiving cartridge.

if they are donated cases i truly do suspect your cases are taking a couple of firings to form to your chamber. Thats why either start with virgin brass, or anneal the case then shoot it.

Many thanks for your time!

My load date for the FC cases I can't remember for sure. I mothballed these when I started to use some once fired Lapua brass AND I had to change powder from Alliant Reloder 15 to Vit. N140. The Lapua also have shrunk. The load data iss 46gr of Vit. N140, behind a 155gr Dyer Optimus HBC
 
Your 7.62 x 51 chamber is more generous than your .308 Winchester sizing die, so the case has expanded lengthwise to the shoulder which displaced brass has caused the case to shrink in overall length.

Read this: http://www.303british.com/id36.html

Lesson:

  • Don't trim brass for a military chamber until you've fired them at least once.
  • Only size cases for this chamber until they j-u-s-t chamber without effort

Hi John

Many thanks for this!

Do you actually mean width wise? If the cases were expanding lengthwise, then I would be OK with case OAL

Thanks again.
 
Your 7.62 x 51 chamber is more generous than your .308 Winchester sizing die, so the case has expanded lengthwise to the shoulder which displaced brass has caused the case to shrink in overall length.

Read this: http://www.303british.com/id36.html

Lesson:

  • Don't trim brass for a military chamber until you've fired them at least once.
  • Only size cases for this chamber until they j-u-s-t chamber without effort


This is correct, along with the point made that your brass, when FL sized, then fired in a bigger chamber will shorten up a bit. Not uncommon at all. You could adjust your FL die to not size as much.
 
This is correct, along with the point made that your brass, when FL sized, then fired in a bigger chamber will shorten up a bit. Not uncommon at all. You could adjust your FL die to not size as much.

Hi snert.

Many thanks for this.

I assume that this achieved by not seating the die fully? But how do I get the correct neck diameter? Do I buy a neck die?

Cam
 
CAM,

Send me a PM and later tonight I can get back to you and we can walk thru this together.

Snert
 
you dont hve to scrap the
Many thanks for your time!

My load date for the FC cases I can't remember for sure. I mothballed these when I started to use some once fired Lapua brass AND I had to change powder from Alliant Reloder 15 to Vit. N140. The Lapua also have shrunk. The load data iss 46gr of Vit. N140, behind a 155gr Dyer Optimus HBC


looks like a full power load, Mr.Snert will give you some solid advice when talk to him about your issues a bit more.

Also if you ever get the chance finding a mentor local to you is the best case.
 
I want to understand what is going on with respect to my shrinking cases.

johnkeilly kindly posted: -

"Your 7.62 x 51 chamber is more generous than your .308 Winchester sizing die, so the case has expanded lengthwise to the shoulder which displaced brass has caused the case to shrink in overall length."

Read this:
http://www.303british.com/id36.html

What I don't understand is that given the above-mentioned link, my chamber is .013 (ish) LONGER than a commercial .308 Win. Therefore, surely after firing in my rifle, my cases should be longer, not shorter?

What am I not comprehending?

Many thanks

Cam
 
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Try this. Hold your hands so that they are palm to palm right in front of your face. Note the distance from finger tips to the heels of your hands. Now pull your hands apart about three inches, keeping the tips of both hands' fingers touching. You will note that your finger tips were drawn down in the process and that the distance from them to the heels of your hands has decreased significantly. This is what happens when you fire a round that has minimal longitudinal clearance at it's shoulder in a chamber that has quite a bit of clearance in diameter in the body. The reason that cases increase in length is a story for another time.
 
Try this. Hold your hands so that they are palm to palm right in front of your face. Note the distance from finger tips to the heels of your hands. Now pull your hands apart about three inches, keeping the tips of both hands' fingers touching. You will note that your finger tips were drawn down in the process and that the distance from them to the heels of your hands has decreased significantly. This is what happens when you fire a round that has minimal longitudinal clearance at it's shoulder in a chamber that has quite a bit of clearance in diameter in the body. The reason that cases increase in length is a story for another time.

Hi boydallen

Thanks for this, but can't I can't grasp the analogy! :oops:

I fail to understand that when I have a case that measures 2.005 inserted into a chamber that is longer and then fired, the case then is shorter post firing.

You say "minimal longitudinal clearance at it's shoulder" but that's not the case (pardon the pun), the 7.62 chamber is .013 longer and therefore the clearance will be significant?
 
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