Firing pin was stopped by primer, but...

[Ol_FlatTop]

I read on a previous thread that when a cartridge is fired the firing pin is eventually stopped by the primer, not by the shoulder of the firing pin against the inside of the bolt. Then I proved it to myself. I measured the cocking piece depth into the bolt shroud at the rear of my Rem 700 CDL 25-06 bolt, and found that the firing pin moves 0.020" into a primer, but 0.047" into an empty breech.

I based my measurements off of the depth of the cocking piece into the bolt shroud when the firing pin is carefully set atop an unfired primer in a dummy round. I did this by slowly closing the bolt handle, while holding the trigger in, on a primed but otherwise empty case. The test primers were seated flush to the case heads.

What I don't understand is why my measurements were identical for both an unsized, multiply fire-formed case and a Full Length sized case where the headspace was,supposedly) set back to saami standards. I thought the FL sized case would be pushed forward by the firing pin until it's shoulder hits the chamber's shoulder.

Is it the extractor that prevents the FL sized case from moving forward into the chamber when the firing pin strikes the primer? I always pictured the brass of a FL sized case flowing backwards towards the bolt face during fire-forming. Am I wrong? Does it really flow forwards towards the leade?

Or maybe the sizing button stretched the shoulder of the case when it was drawn back through the neck.

Thanks for reading! Hope someone might help me with the details.

Dan K.

 

[butchlambert]

Try it with a new primer only and see what happens.
Butch

 

[Ol_FlatTop]

Not sure what you mean. I was slowly lowering the firing pin on new primers,in chambered, empty cases), measuring, recocking & firing, then measuring again.

Thanks for your time,
Dan

 

[butchlambert]

I didn't read your post fully. Have you measured both a fire formed and the fireformed sized case to see if you are pushing the shoulder back in your sizing? Just because you are full length sizing doesn't mean you are bumping the shoulders back. You may be sizing the neck and body only.
Do you have a way to measure if you are bumping the shoulder or not?

Butch

 

[Ol_FlatTop]

That's kind of what I was wondering. Right now I'm not able to measure the headspace for this caliber,25-06). I have a headspace gauge coming in the mail soon.

So it sounds like you're saying the brass in a new or FL sized case does indeed flow back towards the bolt when it is fire formed inside the chamber.

Thanks,
Dan

 

[butchlambert]

The brass fills the chamber when it is properly fireformed. A headspace gage will only tell you whether the headspace is correct on your rifle. You need a gage that will help you measure both the length on your fire formed and sized brass. This is measured from a datum point on the shoulder to the base of your brass.
Butch