Dimpled Primers

[steel89]

Recently I noticed during a hunt that when I chamber a round in my AA 16, the firing pin dimples the primer 'scary stuff'. The bolt/pin is clean. What would cause this, it is doing it regularly.


Steel89

[bwaites]

Pictures would help.

Does it look like a little crater on the moon, with a central dimple and raised edge?

[Drifter]

It's probably a light strike from the floating firing pin, which is normal with the AR platform for a chambered unfired cartridge. Ammo for AR's often has harder primers to prevent a slam-fire, but always exercise caution and watch your muzzle.

[steel89]

Drifter,
The dimple is definitly a light pin strike. I never noticed it before..mabye I just missed it, but the last few looked a hair short of ignition. Mabye it's normal in an AR platform but new for me and definitly an eye opener. Most of my shooting with ARs has been range time so the chambered round is normally fired and the dimple is something I wouldn't notice. Hunting has been different in the sense that I may go several days where the chambered round is not fired but ejected until the next hunt and I do notice the result of the bolt slamming home.

Steel89

[bwaites]

Ah....I see. I didn't realize you were talking about PRIOR to firing. In that case Drifter is 100% correct. I've seen it if I leave my primers a tiny bit high when seating primers. Never noticed it in factory ammo.

[Drifter]

steel89- Next time you have the assembled BCG out of the rifle, shake it front to rear. You should hear the floating firing pin moving back and forth. The pin is hitting the primer when the bolt slams home on the cartridge. Again, it's perfectly normal, but definitely an eye-opener.

[GrantMan]

This is a good reason to check for properly seated primers when using handloads in AR type rifle. Never happened to me but I am guessing you could get a slamfire with a protruding primer.

[LR1955]

Ah....I see. I didn't realize you were talking about PRIOR to firing. In that case Drifter is 100% correct. I've seen it if I leave my primers a tiny bit high when seating primers. Never noticed it in factory ammo.

Bill:

Very common with issued ammunition and the M-16 / M-4 series that uses an inertial firing pin. What it looks like is very small and although it does put a slight dimple in the primer, it is far from being dangerous unless you load and unload that same cartridge many times.

LR1955

[steel89]

Thanks for the responses. As most of my shooting is done with reloads, I'll definitly seat my my primers a little tighter. Glad the forum is back, I missed the volumes of information that makes for good reading and better shooting.

Steel89

[Hoot]

Thanks for the responses. As most of my shooting is done with reloads, I'll definitly seat my my primers a little tighter. Glad the forum is back, I missed the volumes of information that makes for good reading and better shooting.

Steel89

I use a Lee hand primer. As I prime my brass, if the pockets are inherently tight, it's hard to gauge by feel, how far they're in. After each case is primed, I stand them on a flat surface and check to see if I can make them wobble. If they don't, the primer is in all the way.

Hoot

[Selph Arms LLC]

It has also happened to me just something that happens with the AR-15 platform. I haven’t seen any dimples on my Adams Arms piston gun; I ordered an extra spring to see if that will help with the small dent in the primmer. I will let you know if it helps.

[steel89]

My primers are all deep enough so the round doesn't wobble so its probably just the normal characteristic of the AR that I'm seeing. I'll be more aware of the chargin dangers next time, but of all the rounds I've chambered in AR's I've never had an accidental discharge.

Steel89

[StoneTower]

Here is a cut and paste from Armalite:
"Armalite Inc.
P.O. Box 299
Geneseo IL 61254
Tel 309-944-6939
fax 309-944-6949
info@armalite.com

December 26, 1998

TECHNICAL NOTE 10: PREVENTION OF SLAMFIRES

FACTS:

1. A slamfire is the unintentional discharge of a cartridge during loading or locking, without normal hammer or striker fall.

2. Because of inertial energy remaining when the bolt closes, the firing pin of a number of rifle models such as the Ml rifle and carbine, M-14 rifle, and most ArmaLite patent rifles, strikes the cartridge primer lightly upon chambering a round. This light strike normally will not cause the primer to fire, but it is possible. Government 5.56mm (.223) cartridges are loaded with a thick cupped primer to provide assurance that such an occurrence is rare. Government and commercial 7.62mm (.308) primers are not hardened in this manner.

3. The AR- 10 design includes a firing pin spring which reduces the inertial energy of the firing pin to a very safe level. Extensive firing has confirmed that the firing pin spring almost totally cures slamfire without reducing ignition reliability. No case of slamfire or misfire has been observed in an AR- 10 equipped with the firing pin spring.

RECOMMENDATIONS:

1. When feeding single shots, feed cartridges only from the magazine, or use the charging handle to lower the carrier closer to the closed position before releasing it.

2. Assure that the firing pin retarding spring is installed before firing the AR- 10. It is an
important safety device. Never fire the rifle without it.

3. Always assure that the barrel is pointed in a safe direction when loading any firearm.

4. Use only fresh, good quality factory loaded ammunition."

[davidj]

For .223 reloading it has been suggested that you don't use the Winchester small primers.The new copper colored ones are apparently subject to slamfires due to their softer coating.
This is referenced for AR15 type followers and their free floating firing pins.

[LHClarke]

I agree with LR1955, ALWAYS make sure that you NEVER unload an unfired round in an AR-15 and put that SAME ROUND back in the TOP of the magazine. It could cause a slam-fire. Very bad indeed. I am currently having a problem with a new build double-tapping. I am trying to get this figured before I do anything else obviously!! I have always noticed the small indention, but knew this was normal. NOT so much the double tap thing. Scary. Very glad it is going into battery before detonating the second round!!

LHClarke