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Old October 6, 2018, 09:32 PM   #1
napg19
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Light firing pin marks on primer

Anyone else have this happen on their ar15?
I have a Ruger ar556 and a Aero precision build in 5.56. It does not matter if I use original ruger bcg, wmd or bcm bcg in either of the rifles. For ammo I use Federal, fiochi, hornady and mag tech all in 62 grain. I decided not to shoot a round so I ejected it and noticed a light hit on the primer. This happened on all the different ammo no matter which rifle set up I was using. Buffer and recoil spring are mil spec . This constantly happens cause I check it now and then. Any and all help appreciated as always. Thanks.
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Old October 7, 2018, 07:11 AM   #2
9x19
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It is not unusual for the AR platform.
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Old October 7, 2018, 07:52 AM   #3
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You can produce "light firing pin marks" on a round in the chamber by simply pushing the bolt closed rapidly with your fingers .
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Old October 7, 2018, 08:18 AM   #4
napg19
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Thanks guys. Much appreciated.
One less thing for my OCD to worry about, , LOL.
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Old October 7, 2018, 10:20 AM   #5
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The M1 Garand, M1 Carbine, M14/M1A, M16/AR15, AK's, SKS's, MAS 49/56...all have factory supplied free floating firing pins.

If you have a dirty or corroded bolt carrier...the firing pin can become stuck in the outward firing position, resulting in a slamfire by a closing bolt carrier group (BCG).

Slamfires can also occur by heavy firing pin strikes on non-mill-spec primers, or loading & chambering a single round from a magazine; but that's mostly from old semi auto military rifles and not a fully functional AR15, using safe factory/handloaded ammunition.

You can help solve the slamfire problem in the MAS 49/56, by putting a small fountain pen spring on the firing pin shaft, or just buy & install a titanium firing pin.

May I suggest searching the web about the AR15 free floating firing pin, for more detailed information.
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Old October 7, 2018, 12:48 PM   #6
napg19
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Thanks ERNO86.I will check out this info.
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Old October 7, 2018, 02:04 PM   #7
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The light dimples are a byproduct of the free-floating firing pin.
Every time the bolt closes on a cartridge, the firing pin bounces off the primer. Do it to the same live cartridge enough times, and you'll set the thing off with a slam-fire.

...Which is why the military went to a thicker primer cup, and reloading manuals typically suggest using magnum or 'military' primers for use in an AR.
Personally, I use CCI #41 primers for all AR loads with small rifle primers (and CCI 350s [LP Magnum] for .458 SOCOM-based cartridges).

Slam-fires can and do happen. Using a 'tougher' primer cup is one method of helping prevent them.
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Old October 7, 2018, 07:10 PM   #8
napg19
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This explains why a round went off after rifle reloaded itself and I knew I hadn't pulled trigger yet.
All this info is very helpful. If it happens again to me or someone else at the range this will explain why. MUCH appreciated, Thank You All.
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Old October 8, 2018, 07:21 AM   #9
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"This explains why a round went off after rifle reloaded itself and I knew I hadn't pulled trigger yet."

I sort of doubt that since slam fires are often accompanied by parts damage.
It IS fairly common to have an unintentional "bump fire" due to trigger management which is sometimes exciting, upsetting, or embarrassing depending on circumstances and location.
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Old October 8, 2018, 08:36 AM   #10
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Yep, probably bump instead of slam. In all the years I've been shooting, I've had one slam fire. It was due to a high primer. And it caused damage to my AR when it rotated the barrel and sheared off the barrel extension pin. The bad part, I knew the prime was high but had planned to ease the bolt down and fire round. Instead I pulled the charging handle back and let it go when I got into a hurry. I've only witness one other slam fire with a buddies Mak90.
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Old October 8, 2018, 09:47 AM   #11
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napg19 -

Did you have your finger on the trigger, when the bolt was slammed home on the live round that went off accidentally?

When was the last time you fired the AR before the mishap occurred?

Were you using reloads or factory ammo when the mishap happened?

If you had a pierced primer on the last shot before the mishap occurred...the primer could have stuck on the bolt face, or on the tip of the firing pin that could have caused a slamfire.

It's good safe firearm practice too visually inspect each live round before you load it. Keenly check to see whether the primer is set below flush.

You can perform a semi auto AR safety test on the trigger group & safety when it's unloaded, with no live ammunition lying around:

With the magazine removed...

Slam the BCG home from the open position. Put the safety lever in the "safe" position and press the trigger --- The AR's sear should not trip the hammer. Second: Put the safety in the "off" position and press the trigger...the hammer should drop on the firing pin. Keep your finger pressed back on the trigger after you performed that last maneuver...and pull the charging handle all the way back and release it. Slowly release the pressure on the trigger...you should hear the disconnector click on the AR.
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