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texasmac
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Primer bullet push & primer setback
May 29th, 2020 at 2:47pm
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I was reading an old internet link this morning on testing the power of various primers.  I use Federal GM150M match large pistol primers in .40-65 & .45-70 BPCR cartridges.  So, being somewhat bored, I decided to determine how far a primer along would shove a 540gr Paul Jones Creedmoor bullet (16:1 alloy) down the bore of my Browning.  As the photo below displays, the bullet was shoved almost completely into the lands.  The land impressions stop just short of passing the driving band.  No doubt using a softer alloy or a rifle primer would have resulted in the bullet being pushed much further into the bore.

BTW, on a related subject, in an article I wrote some time ago titled, Firing a Black Powder Cartridge - Progression of Events ( (You need to Login or Register to view media files and links)), I made the following comment:

“As the primer ignites, the force from the primer alone is more than sufficient to drive it backward out of the primer pocket until it contacts the breechblock resulting in primer setback unless the case stretches back, contacts the breechblock and reseats the primer flush with the rear of the case head.”

The above is the main reason the softer breechblock face of some older 19th and early 20th century rifles can experience peening around the firing pin hole when firing cartridges with pistol primers which are not as tall as rifle primers & can gain more momentum prior to striking the breechblock face.

Later on in the article I commented on what happens to the primer when firing a full power load. “Although the case locks against the chamber wall the pressure is sufficient to stretch it back enough to reseat the primer flush with the rear of the case.  By the way, if you doubt the case is stretching back to reseat the primer, fire an unloaded case with only a primer.  If the primer remains slightly backed out of the primer pocket but is flush after being fired in a full powder load, it’s a clear indication the case is stretching back slightly, but it’s minimal and is not a reason for concern assuming the headspace and/or head clearance is not excessive.”

In today’s little experiment the primer was certainly setback the amount of the head clearance.

Wayne
  
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Duck_Rider
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Re: Primer bullet push & primer setback
Reply #1 - May 29th, 2020 at 3:20pm
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I can expand a little bit on the difference in primers. I tested large rifle/pistol in a dedicated 30/06 pressure bbl. 18 different primers velocity 2721-2832 fps, pressure 45850-57550 psi same lot cases, powder & bullets (180g Remington Spitzer). Small rifle/pistol dedicated 223 bbl 13 different primers velocity 2701-2829 fps, pressure 32500-41850 psi (55g Winchester Spitzer). All tests 5 shot average. Hope this is usable information to add to prior post.
Harry
  
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craigd
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Re: Primer bullet push & primer setback
Reply #2 - May 29th, 2020 at 3:57pm
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I think there’s been comment before on this? Firing a primed case will lock up a revolver, but when it’s loaded with a bullet and powder, apparently it sets back enough to be flush with the head of a case. I think that was the downfall of wax primer driven practice bullets. Maybe, straight walled pistol cartridges would behave somewhat similarly to many single shot cartridges?
  
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JLouis
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Re: Primer bullet push & primer setback
Reply #3 - May 29th, 2020 at 5:49pm
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What is the actual intent of this conversation? I must be missing something that I don't quite understand.
  
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texasmac
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Re: Primer bullet push & primer setback
Reply #4 - May 29th, 2020 at 6:23pm
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JLouis wrote on May 29th, 2020 at 5:49pm:
What is the actual intent of this conversation? I must be missing something that I don't quite understand.


How far a primer alone, even a mild pistol primer will push a heavy bullet into the bore and how a primer is setback, and then re-seated when fired with a full power load.

Wayne
  
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Dusty Rhodes
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Re: Primer bullet push & primer setback
Reply #5 - May 29th, 2020 at 7:47pm
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Gentlemen, I can tell you this, 
A 22 Hornet with primer only will propell an Air rifle slug, at a very reasonable velocity. 
Ask the nieghbours cat. 😲
  
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JerryH
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Re: Primer bullet push & primer setback
Reply #6 - May 29th, 2020 at 9:26pm
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Dusty Rhodes wrote on May 29th, 2020 at 7:47pm:
Gentlemen, I can tell you this, 
A 22 Hornet with primer only will propell an Air rifle slug, at a very reasonable velocity. 
Ask the nieghbours cat. 😲


Is that with fixed ammo or breech seated? Any particular pellet/primer combo for accuracy? 

Asking for a friend.

JerryH
  
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Mick B
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Re: Primer bullet push & primer setback
Reply #7 - May 29th, 2020 at 9:35pm
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Wayne
I have a question, and seeing as you have done a lot more primer testing than myself perhaps you can help me.
I only shoot BP, mostly Wano PP, I have been using Federal GM155M LMP primers seated through paper so I get consistent ignition, owing to the shorter nature of pistol primers, without the paper, my firing pin in the 44.5 CPA doesn't hit them quite hard enough to secure reliable ignition.
I have also recently tried Federal 155 LMP primers which seem to work as good, and are cheaper as well, whats supposed to be so good about the GM155M compared to the 155 ? I can't see any difference in accuracy so far. I have tried a lot of other primers including LMR primers but my rifle seems to prefer LMP best, this applies to both my 40-65 and my 40-60 Maynard.
Cheers
Mike.
  
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50target
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Re: Primer bullet push & primer setback
Reply #8 - May 29th, 2020 at 10:03pm
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Enjoyed the article and know firsthand in a revolver primer only causes frustration getting everything cleared.

All that said, that picture of the bullet is center fold material to a shooter. Super skill on that one. Funny how certain thins just reach out and grab you.
Thanks for the photo.
Bob
  
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texasmac
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Re: Primer bullet push & primer setback
Reply #9 - May 29th, 2020 at 10:26pm
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Mick B wrote on May 29th, 2020 at 9:35pm:
Wayne
I have a question, and seeing as you have done a lot more primer testing than myself perhaps you can help me.
I only shoot BP, mostly Wano PP, I have been using Federal GM155M LMP primers seated through paper so I get consistent ignition, owing to the shorter nature of pistol primers, without the paper, my firing pin in the 44.5 CPA doesn't hit them quite hard enough to secure reliable ignition.
I have also recently tried Federal 155 LMP primers which seem to work as good, and are cheaper as well, whats supposed to be so good about the GM155M compared to the 155 ? I can't see any difference in accuracy so far. I have tried a lot of other primers including LMR primers but my rifle seems to prefer LMP best, this applies to both my 40-65 and my 40-60 Maynard.
Cheers
Mike.         


Mike,

I can't give you any advice other than to say I've done enough primer testing to convince myself that a weaker primer results in better accuracy than with a rifle primer or magnum primer with my BPCR rifles and loads.  This seems to be the general consensus of many BPCR competitive shooters but some continue to use rifle primers with good success.  I can say the use of magnum rifle primers are no longer in vogue and are not used by any of the serious BPCR shooters I'm aware of.

Several years ago I did try various primers, rifle and large pistol, and the Federal GM150M match gave me the best results at the time so I've stuck with them.  I have not compared them to GM150 standard, figuring the match ones had to be as good or possibly better.

More recently I've completed a bunch of testing using over primer wads & under powder wads.  The following two articles reporting the results may be of interest. 

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Wayne
  
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