#1
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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" |
#2
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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.
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Daryl |
#3
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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.
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#4
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Wrong terminology is all. He was talking about the decrease from the shoulder to the base, I assumed.
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Daryl |
#5
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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.
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#6
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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 |
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