Saubier.com  



Go Back   Saubier.com > Saubier.com Forums > Small Caliber Discussion Board

Reply
 
Thread Tools Display Modes
  #1  
Old 03-19-2021, 12:37 AM
Johnly Johnly is offline
Senior Member
 
Join Date: Sep 2006
Location: Eugene, OR
Posts: 953
Default Dry-firing headspace effects - Test Results

I decided to answer the question using some 223 Federal brass fired in my CZ527 and a RCBS 223 Precision Case Mic. I numbered 10 cases and measured them as fired and after, 1 strike, 2 strikes, 5 strikes, and 10 strikes.
The results were as follows:

1 Strike:
Minimum decrease: .0005"
Maximum decrease: -.0015"
Average decrease: -.0005"

2 Strikes:
Minimum decrease: .0000"
Maximum decrease: -.0025"
Average decrease: -.0011"

5 Strikes:
Minimum decrease: -.0015"
Maximum decrease: -.0065"
Average decrease: -.0039"

10 Strikes:
Minimum decrease: .0003"
Maximum decrease: -.0100"
Average decrease: -.0060"
Reply With Quote
  #2  
Old 03-19-2021, 12:46 AM
Daryl Daryl is offline
Senior Member
 
Join Date: Sep 2006
Location: Prince George, B.C. Canada
Posts: 4,273
Default

Now THAT is an interesting test. It also shows why headspace will increase in some rounds fired with cast bullets. There is not enough breech pressure to ensure the ctg. re-fits the chamber, thus resisting the collapsing of the shoulder.
I was quite surprised at the maximums of 6 to 10 thou.
__________________
Daryl
Reply With Quote
  #3  
Old 03-20-2021, 06:48 PM
Qaz Qaz is offline
Senior Member
 
Join Date: Sep 2006
Posts: 828
Default

Maybe I don't understand what you did, but if you were dry-firing, headspace would have to increase if anything. The firing pin is tapping the cartridge towards the chamber, not the bolt face. If I am wrong, please explain.
Reply With Quote
  #4  
Old 03-20-2021, 07:09 PM
Daryl Daryl is offline
Senior Member
 
Join Date: Sep 2006
Location: Prince George, B.C. Canada
Posts: 4,273
Default

Wrong terminology is all. He was talking about the decrease from the shoulder to the base, I assumed.
__________________
Daryl
Reply With Quote
  #5  
Old 03-20-2021, 08:18 PM
Johnly Johnly is offline
Senior Member
 
Join Date: Sep 2006
Location: Eugene, OR
Posts: 953
Default

Quote:
Originally Posted by Daryl View Post
Wrong terminology is all. He was talking about the decrease from the shoulder to the base, I assumed.
Correct. The RCBS Precision Mic measures the distance from the case head to the shoulder. The change in headspace between the case and chamber is inferred.
Reply With Quote
  #6  
Old 03-21-2021, 04:50 AM
Kevin Gullette Kevin Gullette is offline
Senior Member
 
Join Date: Sep 2006
Location: Wichita Falls, The Republic of Texas
Posts: 1,021
Lightbulb I would expect....

.....that the decreased headspace dimension is NOT from the firing pin hitting the rear of the already dented primer.

Rather that the headspace change is due to the firing pin ASSEMBLY slaming into the rear of the bolt, upon trigger sear release......slightly resizing the fired case. Bolt fit tolerances allow the bolt to move slightly fore and aft. Stripping the bolt, and re-inserting in the action.....on an empty chamber......will show the slight movement.

Hope this helps.

Kevin

Last edited by Kevin Gullette; 03-21-2021 at 04:53 AM. Reason: add
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 04:35 PM.


Powered by vBulletin® Version 3.8.1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.