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

[longdayjake]

As long as the primers are made for semi-rifle use you will be okay. I once made the mistake of using .223 magnum primers in some 9mm pistol stuff I reloaded. I could only get one of about 10 to go off in my glock. And that was trying to get them to go off. A floating firing pin hits a lot softer than a glock hammer.

[steel89]

Thanks for the information and good advise guys. Safety is always a top priority. I'm now very cautious about charging my weapon by letting the bolt slam home. It seems safer to control the bolt a little more when charging, with a follow up on the bolt assist. Live and learn.

[glane5910]

yes, you can get slam fires from a primer not seated fully.

[LRRPF52]

Thanks for the information and good advise guys. Safety is always a top priority. I'm now very cautious about charging my weapon by letting the bolt slam home. It seems safer to control the bolt a little more when charging, with a follow up on the bolt assist. Live and learn.

I've never had this problem, and can really only see it happening with primers not seated deeply and/or the soft primers as mentioned. Feel free to drop the BCG from a locked position on your AR, as long as you have reputable factory ammo, or well quality-controlled hand loads. I eye-ball my hand loads, and prime on the press firmly. All my friends use hand primers, but I prefer priming on the press for some reason...then looking at each case head from the side against the light to ensure there is no primer protrusion.

Also, think about your used cases and especially if you're running them pretty hard, after a few reloads, what happens to primer pockets? Now, lets' say that I seat some really loose primer pockets that don't dislodge when I bang the rim at an angle on my bench, but will that be true with them under recoil in the magazine.........?

Then, loose-pocketed rotten socket perhaps ends up with a protruding primer....gets cycled into battery.....almost.....kaboom!

This is a scenario I have wondered about, which could bypass my QC techniques for primer seating. Who knows? I know I've seated some that gave no resistance, and left me with a very not so warm and fuzzy...

LRRPF52

[glane5910]

In all the years I've carried and/or owned a M-16/AR weapon, I've had one round discharge after hitting my bolt release. It was either on one of my Grendel's or my 50 Wulf. Checked primer protrusion which was fine. Had to be a high primer. Back a couple of years ago when we couldn't find primers, I used some large pistol mag primers(which should be "softer") in my IMI cases to fire form and never had a problem.

[warped]

I've never had this problem, and can really only see it happening with primers not seated deeply and/or the soft primers as mentioned. Feel free to drop the BCG from a locked position on your AR, as long as you have reputable factory ammo, or well quality-controlled hand loads. I eye-ball my hand loads, and prime on the press firmly. All my friends use hand primers, but I prefer priming on the press for some reason...then looking at each case head from the side against the light to ensure there is no primer protrusion.

Also, think about your used cases and especially if you're running them pretty hard, after a few reloads, what happens to primer pockets? Now, lets' say that I seat some really loose primer pockets that don't dislodge when I bang the rim at an angle on my bench, but will that be true with them under recoil in the magazine.........?

Then, loose-pocketed rotten socket perhaps ends up with a protruding primer....gets cycled into battery.....almost.....kaboom!

This is a scenario I have wondered about, which could bypass my QC techniques for primer seating. Who knows? I know I've seated some that gave no resistance, and left me with a very not so warm and fuzzy...

LRRPF52

I saw some cops last year easing the bolt forward after the bolt was locked back, I could not think of why they would ever do such a thing.

I am sure that you and I, Gene and some of the others have probably shot a mountain of ammo from this platform without a slamfire.

Of course we practice muzzle discipline as well so even if it did such a thing, we would not be killing anyone nor destroying something important.

I have recently had some primers go in with virtually no perceived force. The others in the same batch took a bit, regardless I looked quickly at each one as I filled magazines.

Heck I even found that I had three with no primer which is strange because I kept the primer feeder full and have a warning sensor.

I am really considering hand priming anyways.

[LRRPF52]

Warped,

I've done a CQM range before where I literally fired over 1,100 rounds in less than two hours, and they were all on-target (FBI silhouettes). Actually, my avatar pic is of that particular range/day I'm speaking of, and one of the guys that was running it had burnt 10,000 rounds through his M4A1 the day before, after tossing his previous upper and getting the "New" one, which he took to bolt service life in one day. With all the civilian AR's, M16A1's, M16A2, M4's, and M4A1's I've burnt ammo through, I never had a slam-fire, and all my range sessions have usually been no less than 300 rounds on the civilian side. I've never had a slam-fire with a Garand, M14, M1 carbine, or M1A either.

It was more common on the early Armalite AR15's that had a larger firing pin head, which had a lot of mass to it. As they transitioned from the prototypes to the Colt Model 601 (first Colt-made military AR15 with Green painted furniture over the bakelite, chrome BCG, slickside upper/lower) and Colt Model 602 (all black, still "slickside", 1/12 rifling, no chrome bore anymore), they kept the large head firing pin, and as a result of the evaluations and incidents of slam fires with those, they went to the lighter firing pin on the XM16E1 in 1964, which is still the current design.

HK used a firing pin spring and safety plunger on the 416 & 417, but that is classic over-engineering (the plunger). I do like the firing pin spring design on the current Armalite AR10's, but in practice, the floating pins with lighter weights have not been a problem. You can also buy a Titanium firing pin, but the tips have supposedly galled on them when used in AUTO guns.

LRRPF52

[warped]

Yes, this has been similar to my experience.

Last year we tested an AR15 in 5.56mm that ran 4k rounds before a stoppage.

This is not that impressive but what it is that it was a DI rifle and it was suppressed the entire time.

If that did not cause a slam fire what will?

That was the filthiest rifle anyone would ever see.