I understand misfires.  Ammo doesn't go boom.  Easy.

I understand squib loads.  Partial powder charge or fouled powder.  Easy.

I do NOT understand hang fires.  What is there to delay?  What part of the nearly-instantaneous chain of chemical reactions decides to take a breather?

Don't misunderstand, I acknowledge that hang fires happen.  I've got some ancient 8mm Mauser ammo that consistently hesitates for several full seconds before going off.  It goes "BOOM" just fine, but it makes you wait.  But how?

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Could be the primer isn't fully seated, the explosive primer pellet may have been crushed during seating, a tiny bit of the compound may be contaminated by finger oils, or the firing pin impact may be soft due to a weak spring or crud in the bolt. Could also be old or damp powder causing it.

Old guns, old ammo, weak springs.......

As your doctor, I advise you get some Viagra.......

Nope, none of these make sense to me. 

Sounds like the powder is taking too long to burn.

Being that a round travels via pressure build up of the gasses produced by the burning powder, could be that it is burning like a fuse rather than igniting instantaneously.

At a glance, that makes potential sense.  But, if that were the case, I'd expect 2 things, neither of which are happening:
1. I'd hear the primer go off.  I don't.  Just the clear CLICK of the firing pin, a pause, then a boom.
2. POI would be different from the rounds that fired normally.  It isn't.  This ammo groups consistently, regardless of delays in firing (if I do my job)

Could be the primer isn't fully seated, the explosive primer pellet may have been crushed during seating, a tiny bit of the compound may be contaminated by finger oils, or the firing pin impact may be soft due to a weak spring or crud in the bolt. Could also be old or damp powder causing it.

Again, no.  Primer problems could result in no ignition easily enough... no spark, weak spark, misalignment with the flash hole.  None of those would cause a delay, though.  It isn't like the primer's ignition leaves embers lying around that eventually get around to falling through the flash hole. 

Old guns, old ammo, weak springs.......

Well, the gun may be old, but the spring ain't weak! 

This is bewildering to me.  I've done a lot of Google-Fu, and so far, the only thing REMOTELY related I came up with is a government agency that has formulas on gunpowder breakdown over time.  But their reason for monitoring is that they are concerned about spontaneous ignition, not hang fires.

I can't say that I have ever had one, but my Old Man always warned me about the possibility. We used to shoot old .22 and a fail to fire was always treated as a hang fire.
It is ingrained in me and I count to 10 with the muzzle down range before I try to clear the piece.
Old habits die hard.

Gordy

I would have to think that it's a combination of things. Weak spark from the primer barely ignites damp, deteriorated powder that just barely begins to burn. As the combustion process gains momentum, the round eventually fires. That's the only reasonable explanation that I can come up with.

As this usually seems to happen with old ammo, my theory is that moisture seeps in around the primer, either because of a lack of sealant or deteriorated sealant. This would be exacerbated by the ammo being exposed to extreme temperature differentials allowing condensation to form on the cases. Unless the ammo was stored in a vacuum, the air inside the container would have enough moisture in it for this to happen, and the older the ammo the more chances there have been for it to be stored carelessly. I can't say that I've heard of eastern bloc countries being particularly fastidious in their ammo storage techniques.

Just my [ serious] thoughts on the subject. Hope it helps!   

I see what you are getting at Tom - kind of interesting actually.  What's going on inside the casing that could delay from really short to really long (seconds) in duration.

From shooting a lot of  black powder i know that "hang fire" originally referred to most rifles that had flash pans the delay being obvious in that reference. Modern ammunition most hang fires i know of happened so fast there usually unrecognizable. I can't say i have ever had a hang fire like you speak of where seconds go by! Hell i know from dropping 60mm mortars down the tube worse feeling was always hearing that round bounce off the fire pin without firing!! I guess we all take some sort of leap of faith every time we pull the trigger no matter how small that leap of faith is.

The first time I was shooting this stuff, it took me a while to realize that the ammo would eventually go "BANG!"  I settled into a rhythm, and it was actually a fun game.  Boy, you learn a lot about your marksmanship when you don't know how long you've got to keep doing everything right!

Then I had one that didn't go "BANG!"  I waited 10 seconds, 20 seconds, 30 seconds... NRA says that after 30 seconds, you are safe.  But, hell, 50% of these rounds were hang fires... what if this was just a REALLY long one?  So I counted to 30 seconds, then I counted to 30 seconds again, then I counted to 30 seconds a 3rd time.  Then I kept holding the rifle on target while I decided how to proceed, which probably took me another 30 seconds.  Then I decided to work the bolt as quickly as possible while turning my head away from the breech, but still maintaining a firm hold on the rifle.

Then, there was this round sitting on the table right next to me.  So I got up and walked away.  Well, ran.  Ok, I didn't RUN, but I did scurry.  Then I sat down and decided it was a good time for a sandwich.  After that, I was finally willing to pick up the dud round and go toss it in the dud box. 

Yeah, I may have been a trifle concerned...

How about gummy oil sludge in the firing mechanisms?
Maybe that could delay the lock time if the sludge was really bad.
As in retarding the release of the firing pin in a bolt gun.
Come to think of it, since tolerances in most firing mechanisms are tight,
It wouldn't take much sludge to slow things down.
Wd40 gets gummy after a while.
That would be my guess.

I have never had a hang fire myself.

How about gummy oil sludge in the firing mechanisms?
Maybe that could delay the lock time if the sludge was really bad.
As in retarding the release of the firing pin in a bolt gun.
Come to think of it, since tolerances in most firing mechanisms are tight,
It wouldn't take much sludge to slow things down.
Wd40 gets gummy after a while.
That would be my guess.

I have never had a hang fire myself.

While I could see that, I'm pretty sure this isn't a mechanical problem.  I can see the rear of the firing pin, feel and hear the click.  Ignition is delayed a few seconds after all that happens.  Plus, the ad for the ammo warned of duds and hangfires, as did people posting in the comments.

While I could see that, I'm pretty sure this isn't a mechanical problem.  I can see the rear of the firing pin, feel and hear the click.  Ignition is delayed a few seconds after all that happens.  Plus, the ad for the ammo warned of duds and hangfires, as did people posting in the comments.

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What ad for ammo?

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The first time I was shooting this stuff, it took me a while to realize that the ammo would eventually go "BANG!"  I settled into a rhythm, and it was actually a fun game.  Boy, you learn a lot about your marksmanship when you don't know how long you've got to keep doing everything right!

Then I had one that didn't go "BANG!"  I waited 10 seconds, 20 seconds, 30 seconds... NRA says that after 30 seconds, you are safe.  But, hell, 50% of these rounds were hang fires... what if this was just a REALLY long one?  So I counted to 30 seconds, then I counted to 30 seconds again, then I counted to 30 seconds a 3rd time.  Then I kept holding the rifle on target while I decided how to proceed, which probably took me another 30 seconds.  Then I decided to work the bolt as quickly as possible while turning my head away from the breech, but still maintaining a firm hold on the rifle.

Then, there was this round sitting on the table right next to me.  So I got up and walked away.  Well, ran.  Ok, I didn't RUN, but I did scurry.  Then I sat down and decided it was a good time for a sandwich.  After that, I was finally willing to pick up the dud round and go toss it in the dud box. 

Yeah, I may have been a trifle concerned...

LOL ya man that will make the range a little bit more exciting for sure!!

I'd love to see that ad.

If the manufacturer is prominently stating in their advertisements that the manufacturer's ammo is known to suffer from duds and hangfires, then I would imagine that the problem is more of a manufacturing issue, rather than a consumer/equipment issue.

Without knowing all of the facts, it seems like the manufacturer either cannot, or doesn't care to identify and resolve a known issue... which I find rather interesting. 

Caveat emptor.

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What ad for ammo?

My original post said "ancient," and I meant that literally.  This stuff is from the 1920s or 30s, manufactured in Turkey, sold as surplus.  The ad was from the importer, which was a large, commonly-known outfit like Outfitters or Sarco or someone like that.  Their description for the product was straightforward and clear.  It warned that duds and hangfires should be expected.  It isn't like some manufacturer was trying to pass off crap, it was a company responsibly stating the facts about this surplus ammo. 

I bothered to mention the ad because it seems pretty clear to me that, whatever is happening to cause the hangfires, in this case it is independent of the rifle.  I'm sure weak springs and gummy firing pins could cause hangfires, but I am equally sure that what I am experiencing is chemical, not mechanical, in nature. 

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