Secondary "dimple" in fired 45ACP primer

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Metman2

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I've noticed a curious second dimple in some of the fired primers of my Norinco govt 1911 45ACP. Loads were 5.0gr HP38 or 5.0 gr Unique behind a 200gr SWC, using Winchester LP primer.

http://s1093.beta.photobucket.com/u...primer_dimple_zpsf2039d9f.jpg.html?sort=3&o=0

It's as if the firing pin had made a second strike on the fired primer; is that possible due to recoil? The firing pin spring seems OK, certainly not loose.
It's not with every round, only the odd one. I haven't kept track, as I only noticed after tumbling cases, some time after firing.

Not cause for alarm, just interesting.

The Norc is pretty rough on cases.
 
Spawn-Inc said:
i think your over thinking things, but i would look to see how round your firing pin is.
Click to expand...

Doesn't seem to be anything odd about the firing pin. As I said in my original post, I don't interpret this as cause for alarm, it's just a curiosity. For all I know this could be common, with firing pins that rebound, but I just never bothered to look that closely at fired primers. Reloading always by the book, never maxed out, and my round count is approaching 12K since 2007, so far so good!
 
id say get a new firing pin maybe.

Measure the OAL of the firing pin, compare it to a new one. I had an issue where mine started to have FTF's, checked and it was about 20-30 thou undersized. Replaced it, and all was good again.

any FTF's reported lately?
 
it's not a second strike and I will tell you why..

when a round is loaded in the chamber, and the slide slams forward, on some guns the firing pin will slightly hit the primer.. However. if you think of the "shape" of a firing pin, and assume its "round" then if the firing pin hit the primer initially, the second time it's struck (when pulling the trigger), the exact same initial shape would be created, but only deeper and would mask any lighter strike on the firing pin. same thing with if the firing pin hit the primer after the round went off. . thats not to say the firing pin is not striking the primer when loading, but the you would not see "two" strikes on the primer.

Now.. if you think of how firing pins are made, and turned on a lathe, then the "small dimple" is more then likely where the firing pin was cut off from the larger piece of metal.. if you look closely at the firing pin you will probably see the small dimple on the very tip of the firing pin. (looks like a nipple ;) )


to test to see if the firing pin is hitting the primer initially, take a round with a fresh primer, and load it/fire it as normal.. on the second round, do not fire it, but eject it by hand and see if you see a firing pin strike on it. (you might also to do this by loading the first round from the mag by letting the slide slam forward hard.)
 
ckc123 said:
it's not a second strike and I will tell you why..

when a round is loaded in the chamber, and the slide slams forward, on some guns the firing pin will slightly hit the primer.. However. if you think of the "shape" of a firing pin, and assume its "round" then if the firing pin hit the primer initially, the second time it's struck (when pulling the trigger), the exact same initial shape would be created, but only deeper and would mask any lighter strike on the firing pin. same thing with if the firing pin hit the primer after the round went off. . thats not to say the firing pin is not striking the primer when loading, but the you would not see "two" strikes on the primer.

Now.. if you think of how firing pins are made, and turned on a lathe, then the "small dimple" is more then likely where the firing pin was cut off from the larger piece of metal.. if you look closely at the firing pin you will probably see the small dimple on the very tip of the firing pin. (looks like a nipple ;) )


to test to see if the firing pin is hitting the primer initially, take a round with a fresh primer, and load it/fire it as normal.. on the second round, do not fire it, but eject it by hand and see if you see a firing pin strike on it. (you might also to do this by loading the first round from the mag by letting the slide slam forward hard.)
Click to expand...

Interesting explanation. However, it doesn't explain the observations. Why do only a few primers have the second dimple? If it were due to a nipple on the tip of the firing pin, one would expect all or nearly all the primers to exhibit the same feature. When examined under high magnification, the tip of my firing pin is perfectly round, with no nipples or otherwise-shaped protuberances.

Firing pin:
http://s1093.beta.photobucket.com/u...1911FiringPin_zps8db71620.jpg.html?sort=3&o=0

Dent in soft lead that shows roundness of firing pin tip:
http://s1093.beta.photobucket.com/user/nilsek/media/Metmans%20diverse/Norc1911FiringPin_zps8db71620.jpg.html?sort=3&o=0

There is absolutely no sign of the the firing pin striking the primer prior to firing. This does happen with my M1A with its free-floating firing pin. The firing pin spring on my 1911 seems to be stiff enough to prevent that from happening.

My own priliminary explanation - after thinking things over - is that primers are simply deforming due to pressure. The reason that they don't all deform the same way is that thickness or hardness of the actual brass may vary from one primer to the next, such that soft ones flow more under pressure, thus forming a secondary dent within the initial round dent. Visualize a small volcanic bulge forming within a larger crater - a not-so-great analogy but the only one I can think of at this time.
My Norinco 1911 is also loose enough that the lock-up and timing are far from perfect, which also creates some "inconsistency".

Anyway, it's not something I'm worried about, but I like try to understand exactly what's happening. I see no reason why, as a certified science nerd, I can't have enjoy shooting in ways others may not find appealing. To each his - or even her - own.
 
I personally think it may be primer related not due to the gun. Maybe slight variations in thickness of the primers cup deforming differently on the anvil? Meh, either way..
 
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