Ar-15 firing pin safety.


May 21, 2010, 09:27 PM
Does it have one?

If I drop a chambered ar-15 barrel first could it theoretically forcethe floating firing pin forward fast enough to ignite the primer?

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May 21, 2010, 09:35 PM
No it does not have a firing pin block or safety, and that is why they train us not to chamber a round until you are ready to fire or in combat. But I really don't think it will fire from dropping the rifle on the barrel think about how fast the bolt flies into battery when you chamber a round, does the rifle fire then? Chamber a round and then eject it and examine the primer you will see what I am talking about. Most 5.56 ammo has a harder primer cup so it will not ignite during chambering. When you reload alot of manuals reccomend against the softer primer cups which I believe are made by Remington for this very reason, it would cause your gun to fire out of battery and eratically.

May 21, 2010, 09:35 PM
it floats freely. just chamber a round and remove it and you'll see the firing pin actually dented the primer (w/o setting it off)

Steve in PA
May 22, 2010, 02:35 AM
SKS, Garand, M1 Carbine and some other rifles all have free floating firing pins.

May 22, 2010, 07:35 AM
Actually, I prefer Remington 7 1/2 primers for my AR loads or CCI, because they appear to have harder cups. Or maybe because that's what I have available. I have let the bolt slam countless times and have never had a slamfire. I always point it in a safe direction just to be on the safe side.

May 22, 2010, 11:32 AM
I looked it up and Remington SR 6 1/2s are what you are not supposed to use due to the soft cup, I just use CCI white box myself.

Still 2 Many Choices!?
May 24, 2010, 12:49 AM
In a word no....

The firing pin does not have enough weight to ignite a properly seated primer on it's own. The floating firing pin won't make a difference. If speed/mass of the bolt carrier closing the bolt won't do it, neither will a drop. It takes the force of the spring driven hammer to push the very light pin hard enough.

May 24, 2010, 10:36 AM
Remington doesn't recommend the practice of using soft primers, but it's more because the public doesn't like seeing the dimples and won't tolerate them. Military primers get dimpled too, it's not remarked because the weapon cannot fire out of battery.

The length of the firing pin was calculated to be exactly right only when the bolt is closed and fully locked. The firing pin cannot protrude until the bolt head rotates enough, and it shortens the overall BCG length to do so. The locking lugs must be turning into engagement before the firing pin can stick out far enough to strike the primer. Even then it takes sufficient force from the hammer, a free falling pin would have to stop with such force the barrel would be seriously damaged by the impact.

It's not impossible, it's nothing like a Colt SAA. Pull the bolt out and try it, you'll see how it works.

May 24, 2010, 11:21 AM
If I drop a chambered ar-15 barrel first could it theoretically forcethe floating firing pin forward fast enough to ignite the primer?
Unlikely on a chambered AR-15. Would depend on the distance of the drop. I don’t know the velocity an AR-15 firing has to reach to have enough energy to ignite the primer. The acceleration of gravity is 32 ft per second, maybe after a 16 foot to 32 foot drop right on the muzzle. Those velocities probably exceed the forward velocity of the AR15 bolt.

In a word no....

The firing pin does not have enough weight to ignite a properly seated primer on it's own. The floating firing pin won't make a difference. If speed/mass of the bolt carrier closing the bolt won't do it, neither will a drop. It takes the force of the spring driven hammer to push the very light pin hard enough.


Slamfires happened to the early M16’s because of a heavy firing pin and sensitive primers. If you look in Chapter eight, page 130, of the “Black Rifle” by R. Blake Stevens, there is an entire section on the slamfire problems the Army had with the M16. A number of AR15 slamfire incidents had occurred when cartridges were single loaded and the bolt release pressed.

If you read the report in the book, dated 1963, based on the tests of two rifles with the firing pin configuration available at the time, the energy during bolt closure of one of the test rifles firing pin always was above the “none fire” specifications of the primer. Which meant that statistically some of the primers would ignite at those energy levels. So the Army did two things. The first was to test alternate firing pin configurations, all pictured in the book, and one has a spring undoubtedly like the current AR-10 design, and the second was to change the ammunition specifications to require a harder primer.

You can see the different firing pin configurations under Fulton Armory FAQ, the article “Slamfire: the M16 story” http://www.fulton-

I have been collecting posted incidents of AR15 slamfires

AR15 slamfire with Winchester primers.

Occured today while breaking in a new upper ... single round in the mag, pressed the release and ... BANG! A little later on, with three rounds in the mag, pressed the trigger ... round fired. Everything is ok. Pressed the trigger again ... double BANG!

I went back to single loading to finish out the box. Total rounds fired ... 40. Two slam-fires (including the double). Two failures to extract. One failure to feed.

First slam-fire was on the second round fired (while I was still single loading the magazines). The double was on rounds 27, 28 (of 40).

At this point the ammunition is my prime suspect, Winchester "White Box" .223 Rem, 62 grain but I would have to say that ARs do, in fact, slam-fire.

I did inspect for a frozen pin after the first slam fire. I didn't expect one (frozen pin) since I had personally cleaned and inspected the gun last night and it was the second round of the day. I also didn't expect it to foul up too much since it is a piston operated upper (ZM Weapons).

The upper was brand new and unfired (except for factory). The lower is a relatively new (about 200 rounds) RRA. Both (upper and lower) were cleaned, inspected and lubricated properly before the trip to the range. The lower has functioned flawlessly for those 200 rounds when mated to a White Oak Armament upper (all Black Hills .223 Rem 77 grain).

I know BR said that the bolt face could cause the slam fire but the two casings did have firing pin strikes with no other dimples or scratches on the primer face.

I am begining to suspect the recoil spring on the ZM upper. It does seem rather robust. This upper might require the harder primers found in 5.56 NATO. Unfortunately I don't know it all yet so I'm still researching.

Watched an AR Slam-Fire Saturday
Posted 20 April 2009 - 09:10 AM

I was scoring my firing-point partner Saturday during offhand and he had a slam-fire on about the 5th round. We're talking about an experienced shooter here. Multi-year state HP champion, generally shoots 199-clean offhand, not to mention he's a hell of a nice guy. The bullet hit the dirt about 10 yards in front of the firing line. I was watching him closely trying to learn something from his technique, but didn't expect to learn this. I know his finger was off the trigger for certain but his muzzle was decidedly pointed earthward when he closed the bolt. The area downrange is uninhabited for many miles, so at this range folks are a bit lax about closing the bolt while rifle is pointed toward the impact area. After that, he was pretty careful about keeping it level. He was shooting an AR spacegun. He thought it might have been due to the bolt carrier weight he had just put in for testing before this match. My suspicion is high primer, but he could be right. Another possibility is his loading technique. He places the round through the ejection port, then tips the muzzle down and jiggles the round fully into the chamber prior to closing the bolt. I have always thought it best to leave the cartridge on top of the magazine and let the bolt "strip" and chamber it from it's "natural" position. In any event, let this be a lesson to all of us. Closing the bolt is an inherently risky event. Point yer rifle at the backstop when you push that button. My buddy lost the match as a result of his slam-fire, but next time it could be a lot worse.

Posted 20 April 2009 - 10:43 AM

I disagree.

It's happened to me.

I've found that dropping the round entirely into the chamber and letting the bolt close with full momentum isn't the best idea.

I now leave the round resting on the magazine and let the bolt "pick it up" as it closes.

Free-floating firing pins and occasionally sensitive primers can lead to this.

Gary brings up a good point about the trigger issue. Another consideration is the primer. I have seen 2 slamfires in an AR15. Both occured during an offhand string, 2 shots in a row. The shooter is a very experienced reloader and highpower shooter. It never happened again to him. He was using WSR primers. Perhaps it was the primer's "sensitivity," a couple of high primers, or a combo of the two.
The occurance sure did shake his nerves though. Both rounds impacted 10-20 yds in front of the firing line.

Posted 20 April 2009 - 12:02 PM
I had it a few years ago practicing off hand with winchester white box in my service rifle.

Second shot of the night, shot went into the ground in front of me. I put the rifle down and tracked down my 2 ejected brass. Looking at the primer strikes, one had metal flow out into the firing pin hole in the front of the bolt. So, instead of a primer srike like an innie belly button, one of the brass had an outie. No damage to the rifle.

Whats most amazing about your post PamF is the 199 to 200 part!


Posted 20 April 2009 - 12:46 PM
I've had two slam fires and both of them scared the beejiminees outta me. One of the more experienced shooters in my club made the observation that slams seem to happen more often when the muzzle is depresseed as the bolt goes forward. He postulated that the firing pin is already lying forward from gravity almost as if it was preloaded. He figured that as the bolt rode forward with the pin already out, if the primer was gonna go that just gave it the extra opportunity to do so. Since that time I've never let the bolt go forward with the muzzle depressed. I have no idea whether his idea has any merit but it makes me feel safer. For what that's worth. LOL

Posted 22 April 2009 - 11:06 AM
We had at least 2 MIA's over the years at New Holland that had rounds go off when the bolt was closed.
The reason I am able to think of at least 2 is the severe damage to the rifles. In the 2 listed instances the rifles were damaged to the point the receivers were cracked and or broken.
We have an AR-15 do the same thing a time or 2 a year. We have not had rifle damage from the AR-15 slam fires.
My finding at the end of the M1A era and start of the AR-15 era was to completely ensure an AR-15 will not slam fire is to install a light weight firing pin.

Posted 22 April 2009 - 12:31 PM
I had a slam fire several months ago. I was just at my regular local club's range doing slow fire standing practice. Put the round in the ejection port, sort of tipped my rifle forward very quickly to let inertia start the round in the chamber and dropped the bolt. Round went off about 10 feet in front of me. I make an effort to keep the rifle parallel to the ground when dropping the bolt, but get lax about it sometimes.

I was using handloads. Hornady 75gr HPBT, 24.0gr RL15, Remington 7-1/2, LC03 brass. I'm betting the primer was a bit high, because it was once fired brass from military source and I used a Dillon Super Swage tool to just barely swage the pockets (keeping them tight as possible, but still accept a primer).

Posted 03 May 2009 - 08:52 AM
We've had only one instance in the 11 years I've ran local matches. AR15, handload. The same gun has been used many times since w/o any problems. The round impacted the ground 15 feet in front of the line - not a big problem with me compared to having the muzzle raised and the bullet leaving the range.
Me, guess like most, load with the muzzle slightly depressed, drop it in, and hit the bolt release. Bent several rounds trying to drop 'em on the follower. Haven't lost 10 points to slamfire yet, although I have employ many other methods of losing points !

Posted 29 May 2009 - 11:46 AM
I saw two slam fires by the same shooter in the same offhand string.
He was a good shooter who posted a poor score for the day because of this.
I never found out what caused this in his rifle that day but it reinforced the absolute importance of having the muzzle ALWAYS pointed in a safe direction when closing the bolt on live ammunition. (in any firearm)
Both rounds impacted the ground a few yards ahead of him but later, in the same match, I witnessed him closing his bolt with the muzzle well above the horizon. ????????
Bullets impacting the ground will tumble and have a limited flight distance but ones angled above the horizon can pose a much more serious hazard.
Trying to close the bolt with the rifle aimed at the backstop is, in my opinion, asking for trouble. I always keep my muzzle down when closing the bolt and have never experienced a slam fire in my own firearms.
Most folks close their bolts sky high during their rapids and I wish that they wouldn't

Posted 29 May 2009 - 12:33 PM
I had mine to slamfire monday while chronographing some loads. It was completely horozontile on a front rest when I loaded and closed the bolt. I'm just glad it was pointed downrange and wasn't pointed at the chronograph when I closed the bolt. Scared the crap out of me though.
Slamfire, how is it scored?
Posted 21 July 2009 - 12:05 PM
How do you score or count a slamfire? Is it considered as a miss or are you allowed to fire over with another round and disreguard the slamfire? I am referring to having a slamfire while shooting slow fire 200 or 600. The reason I'm asking I have had 2 slamfires one was recorded as a miss at one range and the other one was disreguarded and I was allowed to fire another round in it's place at a different range. Just wanting to know the proper procedure. Tim

Posted 21 July 2009 - 04:05 PM
I never had this happen until I bought some CCI400 primers. The rem. 7.5 never slamfired on me. I'll be glad when the CCI's are gone.
Posted 25 July 2009 - 06:12 PM
I had it happen to me twice in the same stage of a match, standing slow fire, with the newer Winchester SR primers. I was able to borrow a friends extra amo and finish the match. I now only use Rem 71/2's at matches and have never had a problem since. The old Win SR's were harder. I have used CCI mil spec primers on my practice loads with no issues also

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