My first AD just happened

[NavyVet1959]

I had reloaded some rounds for my .300 AAC AR and wanted to check the cycling. First one I tried, the bolt would not go all the way forward, but I could not see any marks on the bullet where it might be touching the lands of the rifling, so I dropped it in the chamber to see if it would seat all the way. It looked good as far as I could tell, so I dropped the bolt on it and then it fired. I was sitting on the couch at the time and barrel was resting on the floor with my feet beside it. Blasted a nice hole in the carpet and a bit of concrete broken out. Concrete/lead splatter hit me in the feet, ankles, and inner arms, but mostly like being blasted with sand. Wasn't wearing my glasses, but nothing major hot in the eyes. All in all, I'm pretty damn lucky.

http://images.spambob.net/navy-vet-1959/ad-carpet-blast-320.jpg

[sparky45]

Glad you're OK, that must have gotten your blood pressure cooking in no time. I to have had some trouble getting 300 BO reloaded ammo to chamber and I've come to realize the brass used to make the 300 BO is critical. Fella on here that sells the brass (Grumpa) can get you the proper info on what brass to use and it all has to do with the thickness at the neck. LC is my favorite to use as well as a few others, but there's lots of manufacturers brass that shouldn't be used, that is if your usage is in a AR platform. Bolt gun should be OK.

[rockrat]

Glad you and anyone around you are OK

[osteodoc08]

Hmmmm. a slam fire? Primers proud? If it wouldn't chamber, did it fire out of battery as well? Glad your safe and carpet/concrete can be replaced rather easily.

Perhaps our knowledgeable folks here can recreate what happened and have a better diagnosis of how it occurred.

[NavyVet1959]

The rest of the mag look good. Safety was on.

[RED333]

Primer brand and type?

[NavyVet1959]

Primer brand and type?

Not sure... I think it was Federal Small Pistol Magnum... At least that is what is on my reloading bench right now. I also use Tula and Wolf sometimes.

[Geezer in NH]

Federal pistol primers are one of the softest going. AR firing pin dents lots of rifle primers I can imagine it firing the fed small pistol especially with the bolt going forward full force not having to strip the cartridge from the magazine.

[gunauthor]

Glad you're OK. I damn near blew my foot off with a friend's 41 magnum. Did get my heart goin'.........

[quickdraw66]

What does the primer look like? Is there a primer strike, or is it flattened? IIRC, the safety on an AR only blocks the trigger, not the free floating firing pin. It's possible that the force of the bolt slamming home was enough to drive the firing pin into the primer and set if off. I've heard of slam fires in ARs before, but they tend to be rare. Soft primers can greatly increase that risk. It's also possible that gunk may have built up around the firing pin, holding it proud of the bolt face. Just some thoughts.

I'm glad you made it though that without an extra hole in you.

[NavyVet1959]

The primer had a raised center portion instead of a dent from the firing pin. That says to me that it wasn't hit by the firing pin and must have gone off when just the body of the bolt hit it.

Tried to duplicate it with my bullet trap as the backstop instead of my floor and it would not occur.

[oneokie]

A multitude of errors; Soft primers, free floating firing pin, closing the bolt on a chambered round.

[country gent]

The raised portion of the primers center is where the firing pin would have been if forawrd and had fired it. More than likely a slightly proud primer and hit of the bolt face was enough with the softer pistol primers cup. Also check bolt face for a burr or raised edge around firing pin hole, this can also aid in slam fires. Another thing to check is the lower corners of the bolts locking lugs for chips or rounding. The same area in the barrel extension should be checked but is much harder to see the faces of the locking lugs there. Am happy to hear no one was seriously injured, following safe practices is always good. Another area to check before firing is the muzzle for obstructions. Having the rifle resting on the floor solidly also may have contributed as it didnt allow the force to flow forward as it would with the rifle unblocked.

[NavyVet1959]

A multitude of errors; Soft primers, free floating firing pin, closing the bolt on a chambered round.

Well, I was needing to figure out why the bolt was not going all the way forward. Dropping it in the chamber looked like it was going all the way in,

Turned out that I need to change my OAL from 2.255" to 2.058" for it to chamber all the way with this bullet profile.

[oneokie]

Tried to duplicate it with my bullet trap as the backstop instead of my floor and it would not occur.
Most likely reason it did not reoccur is the orientation of the rifle. You imply in the op that the muzzle was on the floor with the rifle in a vertical orientation. Trying to repeat the AD with the rifle in a horizontal orientation changes inertia forces.

[petroid]

I have unchambered live rounds and noticed dents in the primer with even CCI SR primers. I have switched to CCI 41 primers for all my AR ammo.
It very well could have been a "proud" primer, but either way, I think a bit harder primer cup can reduce the chance of an accidental discharge.
Glad you are not injured.

[RED333]

Most likely reason it did not reoccur is the orientation of the rifle. You imply in the op that the muzzle was on the floor with the rifle in a vertical orientation. Trying to repeat the AD with the rifle in a horizontal orientation changes inertia forces.
Good point here, with the rifle muzzle resting on the floor, the snap of the bolt going home,
no where for the rifle to move "out of the way". The floor stopped the rifle from moving.

[NavyVet1959]

Most likely reason it did not reoccur is the orientation of the rifle. You imply in the op that the muzzle was on the floor with the rifle in a vertical orientation. Trying to repeat the AD with the rifle in a horizontal orientation changes inertia forces.

Perhaps, but I'm not all that inclined to try to shoot my foot off again tonight. :)

[shooterg]

I useta chamber all rounds to be used in rapid fire stages of HP in the AR it was gonna be used in before a match - BUT I took the firing pin out first. Glad all is OK and hope it's also your LAST AD !

[cuzinbruce]

"Turned out that I need to change my OAL from 2.255" to 2.058" for it to chamber all the way with this bullet profile."

That seems like a rather large change in the OAL. Almost 2 tenths of an inch.

[fryboy]

some days are best with "depends" ( or it sure beats throwing out a now ruined pair of skivvies ... glad you're ok

[NavyVet1959]

"Turned out that I need to change my OAL from 2.255" to 2.058" for it to chamber all the way with this bullet profile."

That seems like a rather large change in the OAL. Almost 2 tenths of an inch.

Yep, but anything less and it will not chamber. 230 gr Lee mold.

[popper]

Full boat load in 308W is even more surprising (CCI LR primer - shoulder was just a hair too far forward). Checked with case gauge and resized the primed cases, no problem. Now I release the bolt with it horizontal!! Did you use a case gauge - bet not. Also, muzzle is down, increases slam fire opportunity, while jammed case doesn't when horizontal. Adjust your FL sizer for proper shoulder location, COL so nothing touches the lands. I've had bore nose jams - typically won't even go into battery. That MG fired LC brass is tough to resize the first time. Haven't had a problem with LC BO brass but I neck turn them.

[OptimusPanda]

That's quite the surprise to have happen. Especially with the safety on and the extractor having to jump the rim for the bolt to close. Ill bet some colorful language was used shortly after.

[Plate plinker]

It's the pin. Glad you are still intact.

[bikerbeans]

"Turned out that I need to change my OAL from 2.255" to 2.058" for it to chamber all the way with this bullet profile."

That seems like a rather large change in the OAL. Almost 2 tenths of an inch.


Yep, but anything less and it will not chamber. 230 gr Lee mold.

NV59,

Good to hear you are okay. I will have my wife read this, she is really tired of me demanding that she have the muzzle of her AR pointed at the dirt when she releases the bolt.

I have loaded and shot hundreds and hundreds of the lee 230g 5R bullet in several different 300 BO and all work fine with an OAL of 2.25". I would download the SAAMI chamber and cartridge drawings and start measuring my ammo and then my chamber until I found the offending dimension. My bet is on the neck OD of the loaded round.

BB

[blueeyephil]

A good reason to use a case guage before loading into a magazine.

[Pee Wee]

Glad your ok

[NavyVet1959]

NV59,

Good to hear you are okay. I will have my wife read this, she is really tired of me demanding that she have the muzzle of her AR pointed at the dirt when she releases the bolt.

I have loaded and shot hundreds and hundreds of the lee 230g 5R bullet in several different 300 BO and all work fine with an OAL of 2.25". I would download the SAAMI chamber and cartridge drawings and start measuring my ammo and then my chamber until I found the offending dimension. My bet is on the neck OD of the loaded round.

BB

I would think that if it was the neck of the loaded round, then pushing the bullet further into the case should not make a difference, but it does.

I am using powdercoated bullets, but that shouldn't make this much of a difference in allowable OAL.

[NavyVet1959]

A good reason to use a case guage before loading into a magazine.

Since it appears to be a seating depth issue, would a case gauge make a difference?

The brass I'm using is brass that I personally converted from 5.56.

[ph4570]

Good to hear that you are not damaged!

[Omega]

Since it appears to be a seating depth issue, would a case gauge make a difference?

The brass I'm using is brass that I personally converted from 5.56.
A cutaway Sheridan case guage will, it replicates the chamber and can check a loaded round or just the formed case. In the cutout you can see exactly where you are having a problem.
147592

[pmer]

Years ago I had a slam fire on the line for the 200 yard standing slow fire. The rifle (AR15 .223) was angled down and the bullet hit to the front of the line. It happened that one time and I finished the course. I was using AA2230 and the firing pin and bolt had carbon build up. I figured the firing pin was sticky enough to help cause the problem. I've seen plenty of those tiny dents on primers before and after that incident. Probably a combination of things making a AD happen.

[NavyVet1959]

Glad you're OK, that must have gotten your blood pressure cooking in no time.

Yep... First thing I did was to do an inventory to see if there were any new holes in my body... The concrete splatter felt like I was getting sandblasted on my face, arms, and feet (even through my sneakers and socks). No one else around and it would have had to go through a few walls (including brick) to exit the building. As far as I can tell though, it just knocked out a spot about half the size of a grape in the concrete and the bullet disappeared. If it had ricocheted while hole, it would have put a whole in the wall in front of me or the ceiling. It tore up a few linear inches of the padding under the carpeting also, but I cannot feel a bullet under there. Strange...

[NavyVet1959]

A cutaway Sheridan case guage will, it replicates the chamber and can check a loaded round or just the formed case. In the cutout you can see exactly where you are having a problem.


The case gauges that I've seen are open at the bullet end and it sticks out, so I don't see how they would help me in determining that the bullet was too long for its profile.

[Chris24]

Sounds like a slam fire with a soft primer. Thank goodness you had it pointed down! I had similar problems when I first started loading .300 BLK. They wouldn't chamber, or worse, get stuck and powder spilled everywhere! The manuals recommend 2.10", but I've had to load them to 2.03-2.05", especially with 7.62x39 bullets. The pressures are low, especially in subsonic loads, so a shorter OAL is still safe.

[Gus Youmans]

NavyVet1959,

At one time Federal small rifle primers had the reputation of being soft, sometimes resulting in slam fires when single loading rounds directly into the chamber and releasing the bolt. I had it happen to me on at least two occasions while practicing for high power rifle matches, so this is not hearsay being passed off as fact. It never happened when rounds were being chambered from the magazine and can only speculate that the bolt and firing pin lost enough energy in stripping the round from the magazine to prevent slam fires. It also never happened with any of the other brands of primers that I used, including Wolf and Tula small magnum primers, Remington 7 1/2 primers, and CCI BR4 and 450 primers.


Gus Youmans

[sparky45]

[QUOTE=bikerbeans;3357060]NV59,

Good to hear you are okay. I will have my wife read this, she is really tired of me demanding that she have the muzzle of her AR pointed at the dirt when she releases the bolt.

I have loaded and shot hundreds and hundreds of the lee 230g 5R bullet in several different 300 BO and all work fine with an OAL of 2.25". I would download the SAAMI chamber and cartridge drawings and start measuring my ammo and then my chamber until I found the offending dimension. My bet is on the neck OD of the loaded round.

That's exactly what I said in post #2. There's a post on this site (somewhere on this site) that has a chart of the different brands of brass and the thickness in the neck area once they are converted to 300BO. Only a few are compatible for conversion such as LC Brass.

[sparky45]

A cutaway Sheridan case guage will, it replicates the chamber and can check a loaded round or just the formed case. In the cutout you can see exactly where you are having a problem.
147592
I have a Sheridan gauge like this and it really opened my eyes to the real reason I was having chambering issues with SOME of the 300's I loaded. Turned out the problem wasn't OAL, but the neck OD. I switched to LC brass and eliminated the problem.

[ole 5 hole group]

Couple things - as long as your muzzle is pointed in a safe direction, you're good to go relative to an AD. Smacking concrete that close isn't all that dangerous and you really need to be having a really bad day to incur a serious injury - but occasionally **** does happen, so I'm glad for you that you were having a good day.

2nd - Federal primers aren't soft - their cup is just as thick as the others and I doubt any "softer" - however, they are more "sensitive" therefore more easily ignited - that's usually a good thing, especially when you need it to go bang or in a no alibi match.

1st AD - you probably haven't had as much trigger time as some others or you are one lucky guy - I think my 1st AD was before I was 16 - had a couple since and that's how I learned an Uzi fires from an open bolt!!;)

Why this one let go - haven't a clue, as "slam fires" are rarer than hen's teeth.

Take care you ole Salt and keep that muzzle pointed downrange.

[popper]

Bolt closing force is only 3-4# at close. Pointed down, gravity helps. FP goes forward when the bolt stops from NO head space, bolt isn't closed. FP zings forward. Bang. Some AKs had the problem with going auto due to the floating pin - solution was a FP spring. A friend has a 22LR that will do the same thing. Do check for proud primers and get either variety of case gauge and USE IT. Sheridan may catch the large neck ones, I just use the wilson. My AD in 308W was powdercoated, not the problem. Had to pogo several, then was checking to find the problem. AR was not against the floor & at 45 angle. Bang, big chunk of concrete missing, boolit powders, didn't even find the GC.
For the BO, I neck turn all to prevent problems. Hand held cutter with the case in an elec. drill - goes fast. I've used Win, CCI, Tula primers in my ARs, none give me a problem.

[Omega]

I have a Sheridan gauge like this and it really opened my eyes to the real reason I was having chambering issues with SOME of the 300's I loaded. Turned out the problem wasn't OAL, but the neck OD. I switched to LC brass and eliminated the problem.
I got this gauge when I was having issues with loading my first reloads. Turned out I did not have my Lee dies set quite right and it would not go all the way into the gauge. I reset the die and took a bit off of the holder and that took care of that. AOL is difficult to fix with this though since it only checks max AOL, but using the AR mag rib and ogive alignment method takes care of most of that for me.

[country gent]

The firing pin moving forward on an inlocked bolt is to short to reach thru by almost .200. The bolt rotates clockwise and back making the firing pin the correct length only when the bolt is closed and locked up corectly. See for your self, pull bolt carrier assemblt out of the upper rotate bolt open in its cam and try an push the firing pin thu to externd out firing pin hole. Then rotate back to closed and pin will protrude thru hole being pushed forward. Its a simple desighn to keep rifle from firing out of battery or going full auto uncontrollably. Until the bolt is fully closed and locked up the firing pin is to short.

[popper]

Country gent - not quite correct. Bolt cam slot/pin design has tolerances. It only takes a few thous., bolt only has to start to lock. As you state, it is a design goal. FP doesn't protrude any 0.2" maybe 0.060. That's why you get to pogo a stuck round, i.e. NO HS. Over sized neck generally won't chamber fully, just like an over sized nose or jamming the lands hard. Full auto is controlled by trigger whatchacallit.

[sparky45]

I got this gauge when I was having issues with loading my first reloads. Turned out I did not have my Lee dies set quite right and it would not go all the way into the gauge. I reset the die and took a bit off of the holder and that took care of that. AOL is difficult to fix with this though since it only checks max AOL, but using the AR mag rib and ogive alignment method takes care of most of that for me.
I load almost all my 300BO with cast bullets. Can't put very much crimp pressure on those lest you chance Leading the barrel and really messing up the gas block. Neck thickness is critical, especially with the new Shilen Barreled 300 I just built. Any brass that is thick at the neck (not LC) WILL NOT go into battery in it's chamber, period. It doesn't matter if the bullet is 110 grain of 247 grain. I size all my cast to .309-.310 depending on which 300 barrel I'm using.

[NavyVet1959]

1st AD - you probably haven't had as much trigger time as some others or you are one lucky guy - I think my 1st AD was before I was 16 - had a couple since and that's how I learned an Uzi fires from an open bolt!!;)

I've had a couple of instances of where a M1911 or other semi-auto handgun will fire twice with one pull of the trigger, but I didn't really classify them as ADs since I had at least intentionally pulled the trigger the *first* time. I probably don't shoot as much semi-auto rifle and some of you do though.

Considering how many times I've intentionally dropped a slide in a handgun on a loaded chamber, this is a bit of a wake-up call.

[country gent]

Yes the disconector on trigger controls sear on trigger from dropping to provide only semi auto. The bolt cam controls runaways or uncontrolled full auto. Just like the connector between sear and bolt on m 14 inside the op rod slot on reciever. this keeps sear from dropping before bolt is locked and running away. Like I sytated earlier pull the bolt carrier assembly and rotate bolt it is pretty much fully closed before pin will protrude. But a raised spot ( I have seen a couple after market bolts with a .003-.005 ridge around firing pin hole, while not alot coupled with a slightly proud soft primer it could contribute). or round with a high primer can slam fire. The ARs sustems are one of the best desighned there is. Measure center of cam slot back to center of cam slot forward or open and it gives a good idea how far the bolt travels locking and unlocking.

[pmer]

A cutaway Sheridan case guage will, it replicates the chamber and can check a loaded round or just the formed case. In the cutout you can see exactly where you are having a problem.
147592

If you don't have one of those Sheridan gauges on hand you can learn a lot about your chamber by measuring a fired case and comparing to a loaded round. You can easily measure how much room your neck has for expansion, check case head expansion and if you are creative you can measure shoulder movement. I use a Stoney Point OAL gauge now made by Hornaday to compare head space. For .223 use a .270 insert and you can reliably measure from the rim to a point on the shoulder and see how much the shoulder is moving between sizing and firing.

And then there is old trick of lightly sizing a unprimed case and closing the action on a backwards loaded bullet to see how long the throat is. The action will seat the upside down bullet and stop at the start of rifling. The OAL gauge helps for a loaded round too.

[Rufus Krile]

If you don't have one of those Sheridan gauges on hand you can learn a lot about your chamber by measuring a fired case and comparing to a loaded round. You can easily measure how much room your neck has for expansion, check case head expansion and if you are creative you can measure shoulder movement. I use a Stoney Point OAL gauge now made by Hornaday to compare head space. For .223 use a .270 insert and you can reliably measure from the rim to a point on the shoulder and see how much the shoulder is moving between sizing and firing.

And then there is old trick of lightly sizing a unprimed case and closing the action on a backwards loaded bullet to see how long the throat is. The action will seat the upside down bullet and stop at the start of rifling. The OAL gauge helps for a loaded round too.
So... what are you gonna do with that couch?

[jkl1861]

Glad you weren't hurt. I trust there's no secondary injuries? Pretty sure my wife would patch the hole with pieces of my hide!

[Moonie]

My 300 has a slightly tighter chamber than my sons. I have to neck turn all brass if I use boolits larger than .309 as 1 out of 5 will not chamber all the way if I don't. My sons upper chambers all rounds. If you are powder coating then you are increasing the diameter of the bore riding section which can cause the rounds not to chamber all the way. I actually will use mold release spray on the noses of molds that have issues like that.

[Friends call me Pac]

Did you have a magazine inserted or did you have an empty magazine well when it went bang? The reason I asked is because I had a slam fire about 3 years ago with my AR 15. I had forgotten a mag so I was loading the rifle 1 cartridge at a time. I would drop the cartridge in the chamber & press the slide release. I did this for numerous rounds until the slam fire happened. I dropped the cartridge in and when I released the bolt POW! My barrel was down range and angled down. I know for a fact my finger was nowhere near the trigger.

I called a friend of mine I served with. He spent 24 years as a combat arms instructor & maintenance troop. The first thing he asked was if I had a magazine in place. Seems when the slide is released without a mag in place, combined with the downward tilt is just enough extra inertia to allow the firing pin to engage. He said he had never seen it happen with a mag in place, only when self loading one by one & no mag. He also told me to go buy a lottery ticket because it is extremely rare but it happened to me.

My AR was the standard 5.56 I don't know if yours being a .300 makes any difference or not since it is the same weapons platform.

Anyway that's what I was told.

[Gus Youmans]

Friends,

I know from experience that slam fires will occur with an empty magazine in place. On the other hand, I have never had a slam fire when the round was fed from a magazine instead of dropped directly into the chamber. I am surprised that your friend had slam fires with military ammo but he probably has more experience in single loading military ammo than I do. All of my slam fires were with my reloads using commercial primers.

Gus Youmans

[Rufus Krile]

The solution is harder primers... CCI#41 rather than #400... if you can find them. AR's are spooky little things that put an ugly mark on every primer that it feeds... that's generally enough for me to me to ease the bolt down and use the forward-assist when seating the first round. OK, so I'm a sissy and don't like sudden loud noises.

[NavyVet1959]

AR's are spooky little things that put an ugly mark on every primer that it feeds...

Well, mine decided to put an ugly mark on the carpet and slab... :)

Pretty much destroyed a piece of carpet about the size of a racketball.

It was probably about 30-45 degrees from vertical when it fired. I was sitting on the couch and the barrel was resting on the carpet when it fired right between my feet. I had a "solvent trap adapter" plus a 3/4" PVC pipe fitting acting as a thread protector. I know what people supposedly use the "solvent trap adapters" for, but I bought it for the purpose of having a common thread for a compensator that I was wanting to build. I figured I could have a single compensator and just use thread adapters for the various calibers. Yet another project that I did not get around to completing.

I hear that you will not die as long as you do not complete all of your projects... I'll let ya'll know how that works out for me... Or not... :)

[montana_charlie]

The rest of the mag look good. Safety was on.
When 'testing' a round that seems to have a fault of some kind, I suggest that you never do that with a magazine installed.
If one round can go bang when it should not, the rest of the mag might follow suit.

It could be that having the safety on prevented a real exciting dance in your house.

I was present (in Vietnam) when an M16 decided to runaway.

I was to the left of my buddy when he pulled the trigger for a single shot.
But, the gun kept cycling.

I reached over and hit his mag release button with my left thumb, which starved the gun into submission.
I was pretty quick, but ten or more rounds still smoked out toward the perimeter.

The problem was a blown primer lodged under the trigger assembly.

[NavyVet1959]

When 'testing' a round that seems to have a fault of some kind, I suggest that you never do that with a magazine installed.
If one round can go bang when it should not, the rest of the mag might follow suit.

It could be that having the safety on prevented a real exciting dance in your house.

I was present (in Vietnam) when an M16 decided to runaway.

I was to the left of my buddy when he pulled the trigger for a single shot.
But, the gun kept cycling.

I reached over and hit his mag release button with my left thumb, which starved the gun into submission.
I was pretty quick, but ten or more rounds still smoked out toward the perimeter.

The problem was a blown primer lodged under the trigger assembly.

I guess I didn't explain it correctly. Initially, I had tried loading from the mag and the action would not completely close. After trying that a couple of times with the same round reloaded into the mag, I removed the mag and tried dropping that single round into the chamber and pulling back the bolt and allowing it to drop. There was no mag in it at that time, so no way could it have had a runaway.

In your case though, I have one question... Did your buddy at least end up hitting what he was originally shooting at? :)

[montana_charlie]

In your case though, I have one question... Did your buddy at least end up hitting what he was originally shooting at? :)
We weren't in a gunfight at the time, and never even wondered about what he may have hit.

EDIT ... In case anyone is wondering about 'where bullets go' in the incident I described:

This occurred on top of Nui Ba Den mountain, near the Cambodian border.
We typically chose rocks, stumps, and other natural objects as targets when test firing weapons, or just practice estimating various ranges.

We did not shoot against a backstop, but we were way too far from anywhere for there to be a danger to passing civilians.
Nobody lived out in the forests where our bullets impacted ... nobody other than Viet Cong and NVA troops.

So, when Mike's M16 did it's runaway thing, we were not worried about shooting out the neighbor's window.

[blueeyephil]

One thing I do when developing a new loading is to make up dummy rounds with no powder or primers. Just to make sure everything loads and ejects ok. Because I've had trouble with length problems with some bullet profiles. First check with the case guage and then in the chamber.

I have one of the new Lyman multi case gauges. It will not help you with OAL like the Sheridan, but I works for 6 cartridges and costs less too. I would love to have the Sheridan with the cut out.