High primers and slam firing

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John Travis

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In the course of the discussion on firing out of battery, a member brought up the point of a slam fire/kaboom due to a high...or incompletely seated primer...so I thought it might be a good opportunity to address it. While a slam fire can happen due to a high primer, the belief that it would be catastrophic isn't founded in anything factual.

The 1911's headspace is generous. with a minimum spec case length and maximum allowable static chamber length, a pistol can have a full 32nd inch of headspace and still pass an armorer's GO-NO GO test.

Very few show that level of headspace, though and most off the rack pistols fall somewhere between .010-.012 inch over minimum chamber length...breechface to stop shoulder...with case length falling between .888 and .890 inch. Add those figures and we have right around .022-.024 inch of working headspace.

With a primer seated .030-.032 inch proud of the case rim, that would mean that the slide is .006-.008 inch from full battery when the slam fire occurs...if it occurs. The upper lugs would be fully engaged vertically, so the breech wouldn't open and thus no kaboom. It would be a little unnerving, but as they say...no blood/no foul.

Moving on to a grossly high primer...let's say in the range of .050-.060 inch above the case rim.

It's highly unlikely that such a badly seated primer would be overlooked, but we''ll assume that it was.

Subtracting the .022-.024 inch of working headspace, the slide will now be only about a 32nd inch out. Still not enough to allow the breech to open. A far cry from being enough, in fact.

And even if we assume tight headspace, such as in a match grade pistol with a .900 chamber, .890 case length, and a .060 high primer, the slide will only be .050 inch out of full battery when the breechface slams into the primer. Still not enough to allow the breech to open. No kaboom.

Whenever people throw out such phrases as "Fired out of battery" or "Slam fired" to explain a kaboom, it seems to make sense to the average Joe, but when subjected to closer scrutiny by someone who understands how the gun functions, it just doesn't hold up.

Here it comes...

Wait for it...

You knew I was gonna say it...

John Browning wasn't an idiot.
 
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Yer gonna get tired. The internet has more believed falsehood than any one man can counter. As that Queen once said, if she'd had a 1911, "Let them eat ignorance." Course, if she'd had a 1911 they might not have lopped off her head either.

I actually quit trying to educate years ago when I was advised a brass saa backstrap was dangerously weak for use on a 357 revolver. It's enough to know they are breeding and so, I hide! :)
 
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Sharps40 said:
I actually quit trying to educate years ago when I was advised a brass saa backstrap was dangerously weak for use on a 357 revolver.
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Well, since my eyes have betrayed me, I can't do a lot of the close work any more, and...as they say...those who can't do, teach.

Even so, I don't get into most of these threads unless I'm invited in. Call my name and I'll be there. Otherwise, I sit on the sidelines.
 
Can a high primer interrupt feeding by catching on the bottom of the breech face or is the extractor hook far enough out there thats just not possible?
 
I had a slam fire once with a high primer, but it was in a Mini 14 and not a 1911. Those are quite different firearms when it comes to feeding. The only problem I have ever had with high primers in a 1911 is having to have the hammer fall twice to set off the primer. Nothing bad happened in either case, and I identified the causes of the high primers and fixed them.
 
Charlie said:
I had a slam fire once with a high primer, but it was in a Mini 14
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Are you sure it wa a high primer and not the floating firing pin contacting a soft or sensitive primer? I've known of Garands and M1As doing that with Federal primers. At one time, CCI offered a mil-spec line of rifle primers that were a little harder to set off for that vry reason.
 
John Travis said:
At one time, CCI offered a mil-spec line of rifle primers that were a little harder to set off for that vry reason.
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Still do. The CCI #41 primer has a different anvil that sits further from the base of the primer making it harder to ignite. CCI #34 is the large primer version.
 
John Travis said:
Are you sure it wa a high primer and not the floating firing pin contacting a soft or sensitive primer? I've known of Garands and M1As doing that with Federal primers. At one time, CCI offered a mil-spec line of rifle primers that were a little harder to set off for that vry reason.
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I am pretty sure it was a high primer. That batch of 223 I loaded had high primers due to the primer pockets being distorted a bit when I swaged them with a Dillon swager that was not properly adjusted. It was all my fault in not inspecting the loads as carefully as I should. The round that slam fired was among the first of that batch I fired. I pulled the rest, groomed the primer pockets, and repacked the rounds with new primers. Those primers were either Winchester or CCI standard small rifle primers. I have used those primers in many thousands of rounds in that rifle in the last 50 years with no problems. I now use the mil-spec CCI primers in my 223, 308, and Garand loads.

It is possible that the floating firing pin was the culprit, but the high primer was obvious. I suppose I should have inspected the fired round to see if there was much of a firing pin dent, but those Mini 14s throw the cases a long way. Finding that particular case would have been problematic.
 
Charlie said:
I am pretty sure it was a high primer.
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The reason I'm wondering is that because of the tight headspace typical of most bottleneck rifle cartridges, a primer sitting only a few thousandths past the rim would serve as a pretty good NO GO gauge and prevent the bolt from going to battery...which could make for a very bad day if it did actually slam fire from bolt impact alone.

I guess things like this is part of what make guns so fascinating.
 
I cannot say for sure one way or the other. I just reasoned, perhaps incorrectly, that that Mini 14 bolt slamming forward as hard as it does against a high primer seated in a pocket with an irregular bottom could set off the primer. The fact that the rifle was in battery enough not to cause an ugly event has troubled me a bit trying to figure out whether it could occur. Perhaps I have just been trying to blame the event on a problem I could fix. Guns are, indeed, fascinating.
 
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