View Full Version : I blew up my AR!!!!!!!!!!!!!!

October 28, 2006, 04:18 AM
I need some ideas on what to look for here. Earlier tonight, I blew up my 4 yr old Bushmaster AR-15. By "blew up", I mean totally destroyed it beyond repair.

Because of the serious nature of what happened, I am going to walk you through exactly what happened including the nitty gritty details. Maybe someone can figure out what exactly went wrong. I apologize if it gets boring, but like I said, detail may mean everything.

My shooting partner and I spent last Sunday reloading our ammo, (.223s) like we usually do in my workshop while the wives were upstairs doing what ever it is wives do when they get together and the kids playing. (My partner and I have been best friends, almost like brothers since we were in grammer school and our families are very close. We have Sunday dinner together every week-end and have done so for many years so, when it comes to reloading me and my friend work like a perfectly tuned and oiled machine). We were using only once fired Remington Brass, which we bought last week (what we do is, one week we will buy ammo at the local gun shop, use it, collect our spent brass and then reload it for the next time we shoot. It saves us alot of money). All of the brass we reloaded , as I said, was only fired once. When we reload, we always faithfully use the same brand powder, same brand primers and same weight leads to keep our shooting results consistant. To us, shooting is a very important sport and is something we have been doing together since we were teen-agers, and we have invested alot of money into our weapons, shooting gear and reloading equipment so we have a proceedure in our reloading that we follow religiously (some say we have boring lives, LOL!) First, we remove the spent primers and as we do this we inspect each and every spent case for any defects such as excessive burn marks, cracks, ect. I check it first, then he does or visa-versa. If we find even one single thing in question, we toss the case into our recycle bucket. After we inspect the brass, we clean the inside of each case with powder solvant and run it through a mechanical tumbler to polish it up. After this is done, we will recheck it, toss any ones we don't like and then get down to business. Next, we use a set of calipers to check the case measurements. We make sure our cases are consistanyly one size. If we find any that need to be trimmed, we will then trim them to size. We then chamfer/ream the necks by hand, ream out the primer pockets by hand and then clean up any burrs. After this is done, we use an air-chuck to blow out any shavings that may be left behind (using low pressure, about 10psi). Next, we reprime the brass using an RCSB auto-primer attachment on my Rock Chucker press. One of us will put the primers in and the other will check each case to make sure they all are uniform in the case. If we find any that aren't uniform, we will pop out the primer and reinstall a fresh one. Then we calibrate the electronic scale we use (we do this every time we reload) and recal the powder dispenser. We will individually weigh each powder load we pull before filling the cases to make sure they are all exactly 24.5 grams on the money. One of us pulls the powder and weighs it, the other will pour the powder into the cases. After all the cases are charged, we will pop in the leads. After all of this is done, we will once again check the bullet length using the electronic calipers to insure uniformity, and then, each completed cartridge will be weighed to again ensure uniformity. After one more quick visial inspection on each one, we will end the session by putting the finished product into plastic cartridge holders and then into our ammo boxes, and the boxes go into a humidity controlled ammo safe. Some may say we are crazy for taking so much time and being so nit-picky in our reloading, but, as I said before, to us, shooting is a very important part of our lives, we take it as serious as some guys take sports like football, and, we have noticed since we became so anal about our reloading technique that our scores have actually improved by a wide margin. Uninterupted, we can usually completely reload a good 400-500 rounds in a good night. During our reloading operation, we do not consume any alcohol and try and keep distractions to an absolute minimum.

After we finish, we will end the night by cleaning our rifles and cleaning up my workshop. (Are ya bored yetLOL!)

Ok, after work today, I went home and picked up my 4 yr old Bushmaster AR-15 and the ammo we reloaded, and met my friend at our gun club. The weather here has absolutely sucked for the last week, heavy rain and temps in the upper 30s to mid 40s. We set up and started shooting at 200 yards without scopes. We make it a point that after each 100 rounds fired, we give the weapons a quick but thorough field cleaning. Anyway, somewhere around 120 or so rounds each into our shooting, (we slow shoot, manually loading one cartridge at a time) I put a round in, took aim (I was shooting in the kneeling position) and squeezed off the round. The round just blew right in the rifle. It went off so hard that it actually blew a small piece of the lower reciever off (if you took a dime and cut it into 4ths, that is how big the piece was). It sounded and felt like someone lit off a cherry bomb in front of me. The blast caused me to reflexively drop the rifle, but because of the way I was using the sling, it didn't hit the ground, except for the buttstock. Luckly, I didn't get hurt, just scared ****less. After I regained my senses and telling my buddy and the other 4 people who were shooting that I was ok, did I look at my AR. It was wasted. Aside from the little piece missing from the lower reciever, the the immediate other damage I noticed was the fire select was pushed out, the front pivot pin appeared bent, the takedown pin was gone and the trigger was completely jammed.
Being as pissed as I was, we packed it in and went straight to my house to strip the rifle down to see what else was damaged. With some difficulty due to the bent pivot pin, we managed to open it up and found the following:
trigger assembly broken and scorched, firing pin in two pieces, firing pin retainer broken, gas rings scorched and broke, forward assist shaft slightly bent and pieces of the broken brass casing jammed up in everything. The lead slug was stuck in the barrel about 10 inches down (my AR has (uh, had)a 20 inch barrel). Also, every part in the recievers was scorched from the powder in one way or another.

There you go. The details. Can anyone take a wild guess on what could have gone wrong? My first thought was maybe we accidently double charged one of the cartridges, but as I said, we weigh each one AFTER we complete the reloading procedure. My friend seems to think maybe it was caused by some type of blockage in the barrel, but I dunno with that much damage. Any ideas will be appriciated. I am going to have a qualified gunsmith look at it and see if he can figure out what happened and if it is salvageable, hopefully most of it will be, but I know the lower is gone along with the trigger and a few other pins and parts. For now, I guess I will be taking a break from shooting until I replace the AR or have it repaired.

As I said, any ideas will be appriciated, and as soon as I can figure out how to do it, I will post the pictures we took of the rifle before we disassembled it and after, showing the damaged inners.

October 28, 2006, 07:18 AM
My first thought would be a bullet remained lodged in the bbl, but I believe you would notice a squib.

I wonder if the bolt was not locked up with the bbl. The bottom of the carrier should keep the hammer from striking the firing pin of it is not all the way home.

Have you checked out the guys at AR-15 com? There may be somone over there who has more info than I.

I'm glad you are ok.

October 28, 2006, 07:51 AM
OUCH!!! Well here goes.It is possible that you didn`t have enough powder in the case so when it fired the powder didn`t burn,it detonated,just like a little bomb in the chamber.The AR15-M16 should not fire the round if the bolt is not locked fully into the barrel extension(breach).I`m guessing the bomb in the chamber thing.

October 28, 2006, 09:09 AM
Was the upper receiver and bbl damaged? Or was the damage to the lower and fire control group?

October 28, 2006, 09:41 AM
Having suffered through your third paragraph, I'd hazard a guess that God's just made an attempt at saving you from hours and hours of superfluous reloading tedium. :)

Ever tried to put 49 grains of any powder in a .223 case? Can't be done; you didn't doublecharge, that's for sure.

October 28, 2006, 10:00 AM
I had a .223 blow up in my face...twice! These were both hand loads made by me in my shop. The backs of the cases blew off...the first one was just a bang and a few minor powder burns on my face. I thought..hmm..bad case. The second one destroyed the rifle and put shrapnel into my face.
I concluded that it was an ammo problem so I had an expert look at the blown up cases and some more of my un-fired hand loads.
It turned out that my de-burring process was not doing the job. It was leaving a slight ridge around the outside of the neck of the case. That ridge was being crimped even tighter when the cartridge was chambered. Some ridges were bigger than others and at some point, it took less pressure to blow the cartridge up than to push the bullet out the front. Big BOOM!
I disabled all remaining ammo that I had loaded. Also just FYI: The chamber area of the barrel had many hairline fractures that were not visible to the naked eye.
Kep yer powder dry, Mac.
Tuff-Gun Finishes. The Name Says It All.
Mac's Shootin' Irons

October 28, 2006, 12:17 PM
I would almost bet it was a bore obstruction of some kind.

October 28, 2006, 01:31 PM
You keep saying lead. Were you shooting cast lead bullets or copper jacketed bullets?

October 29, 2006, 12:57 AM
DnPRK, by "lead", I mean the projectile. We always use the same reload 'formula', never more than once fired (by us) Remington brass, 67 grain FMJ Federal 'leads', CCI primers, and 24.5 gr of premium (the "good stuff" as we call it)Winchester powder. (One of my club members thought maybe we combined the bottom of one can of powder with a freshly opened one and it caused the problem, but we never mix powder from one can to another. If we have left-over, we will reload more until it is gone, or just pop a fresh can.)

Well, I spent a better part of this morning "performing an autopsy" on my rifle as my wife called what i was doing trying to humor me out of the really nasty mood I was in over this accident (sorry, honey for being such a grouch). I went over every square inch of the thing, looking for even the smallest tell-tale sign of what may have happened. I couldn't find anything at all that was or appeared to have been wrong with the rifle. My shooting partner Scott stopped by to see how I was making out and to show me something he discovered. It seems that maybe 1/4 of our brass that we picked up after the accident looked like there was a slight inward 'ding' just below the neck rim. The rest of the brass seemed fine. We grabbed about 100 of the remaining loads and headed to Scott's house to get his rifle, the same model Bushmaster as mine and then drove out to the club, despite the weather, which was almost as foul as I was at this point. Scott's rifle is identicle to mine, except his has a different trigger. We managed to fire 60 rounds before the 30mph+ wind started making the rain unbearable, and after collecting all the spent brass, we headed back to my house to examine it. Well, none of the brass had the 'ding' in it. For haa-haas, I decided to see if I could dislodge the bullet that was stuck in the barrel of my AR without damaging it any further, and after a few minutes of working at it, pushing it out towards the muzzle end with a wooden dowel, I managed to get it out. Sure as hell, there was a 'groove', more like a very small scratch, in the slug's copper jacket. The fore-end of the barrel is scorched pretty bad and slightly messed up from the explosion, but I am now leaning towards what Mac's and Rangemonroe are hinting at, some type of bore obstruction or something like that. Maybe there was something in my barrel that caused the rim to crimp down on the bullet and cause the round to detonate. It would explain the marks on the spent brass, which obviously didn't come from Scott's rifle. I am wondering if maybe when I ran my cleaning rod through the rifle that maybe the steel rod nicked the end of the barrel just enough to damage it in a way that it would cause this.
On the happier side, my wife called our insurance agent while we were out at the club 'playing detective' and she found out that the policy we have for our firearms will cover about 80% of the cost to replace the rifle. Our agent told her that because the gun was destroyed by means other than theft, negligance or misuse, we are covered. I am glad we opted for the better policy when we bought the policy 2 yrs ago. Yes, our premium is slightly higher than the standard no-frills policy, but I can now see the extra $40 a year was worth it. On Monday, i am dropping the remains of my AR off to a friend who is a certified gunsmith to have him look at the rifle to see if he can figure out what the exact cause was, but now, I am going to show him the brass and see if my theroy floats. I will post what his opinion is as soon as he finishes.

October 29, 2006, 01:37 AM
I am wondering if maybe when I ran my cleaning rod through the rifle that maybe the steel rod nicked the end of the barrel just enough to damage it in a way that it would cause this.

The cleaning rod theory isn't very likely. I spent 12 years in a Army arms repair shop, and never saw cleaning rod damage that would cause something like this and Army cleaning rods are steel.

What did the bolt lugs and barrel extension lugs look like? Were they sheared off or mostly intact? Did any of the cartridge case survive? What did the chamber look like?

If the lugs aren't sheared, it looks like the bolt never locked. Since the bullet was only 10" down the barrel the gas never reached the gas port, and the bolt carrier wouldn't have moved rearward to unlock the bolt. That can only mean the bolt didn't lock.

Is it possible the cam pin broke? That would keep the bolt from rotating and locking, but not prevent the bolt and carrier from moving fully forward.

October 29, 2006, 05:57 AM
Sounds like it fired out of battery!

October 29, 2006, 09:26 AM
Like the cam pin broke

Maybe the cotter pin was not put in?

I was thinking the same thing, if the bullet was lodged in the bore, "south" of the gas port...it had to fire without being locked up.

Is it possible that there was a "double feed" with the tip of the second round detonating the primer of the first?

On the happier side, my wife called our insurance agent while we were out at the club 'playing detective' and she found out that the policy we have for our firearms will cover about 80% of the cost to replace the rifle. Our agent told her that because the gun was destroyed by means other than theft, negligance or misuse, we are covered.

I would not ever use my homeowners insurance to cover anything but catastrophic losses. State Farm and Allstate are known for cancelling policies after the very first claim. Try getting insurance after being cancelled! :eek:

After your deductible is paid, how much is 80% of a Bushmaster? $500-600?

October 29, 2006, 10:50 AM
We will individually weigh each powder load we pull before filling the cases to make sure they are all exactly 24.5 grams on the money

It couldn't have been 24.5 grams in a .223/5.56 - what was the powder charge when you pulled down one of the loaded cartridges? Grains maybe?

Guessing the powder is 748 I don't see that as an issue assuming 24.5 grains and certainly not blowing the rifle AND lodging the bullet with anything even close different lots or not.

It does sound to me as though the rifle fired unlocked - I'd doubt a barrel obstruction that was forward of the lodged bullet and disappeared - pushed out by the airflow ahead of the bullet and yet blew the rifle rather than ringing the barrel. I'd do a mag penetrant dye check and look for previous cracks or signs of improper assembly crimp what have you.

I understand the rifle was fired 100 times with the reloads from the same lot then opened and stripped for cleaning then reassembled and fired about 20 times with good results then fired once more for a kaboom?

somewhere around 120 or so rounds each into our shooting, (we slow shoot, manually loading one cartridge at a time) I put a round in, took aim (I was shooting in the kneeling position) and squeezed off the round. The round just blew right in the rifle

What is your process for single loading? Do you use some sort of single shot adapter -SLED style or a single load through through the ejection port with an empty magazine or feed from the magazine? Maybe a bullet setback?

October 29, 2006, 02:30 PM
I would have to agree with Alakar.
If the lugs aren't sheared, it looks like the bolt never locked. Since the bullet was only 10" down the barrel the gas never reached the gas port, and the bolt carrier wouldn't have moved rearward to unlock the bolt. That can only mean the bolt didn't lock.

Being you were shooting these single style it would be more understandable that the bolt was not fully close.

James K
October 29, 2006, 08:33 PM
Unless the firing pin is protruding (due to breakage), it is impossible to get an AR-15 to fire without being locked. And if the firing pin is protruding, the rifle will fire as the bolt closes; it won't wait until the trigger is pulled. I think some more analysis is needed.


October 30, 2006, 12:11 AM
Just a guess here - Did you "ride" the bolt handle down as you were loading the single-shot rounds?

October 30, 2006, 12:46 PM
Unless the firing pin is protruding (due to breakage), it is impossible to get an AR-15 to fire without being locked. And if the firing pin is protruding, the rifle will fire as the bolt closes; it won't wait until the trigger is pulled. I think some more analysis is needed.

If the cam pin breaks a AR-15 can fire without being locked. The bolt and bolt carrier can slide fully forward into battery, but the bolt never rotates to engage the locking lugs. I have seen this occur only twice. Usually a broken cam pin will not break cleanly and will jam up the action of the weapon. But on those two occasions, the cam pin broke cleanly at the surface of the the cam pin hole in the bolt. When the carrier came forward the bolt was able to slide back into the carrier making it look like the weapon was locked.

We tested out the theory with one of the broken cam pins. We installed it in a functioning weapon, let the bolt and carrier slide into battery, and were able to push the bolt and carrier assembly back by pushing on the bolt face with a cleaning rod down the barrel. In this instance, the problems were caused by a bad lot of cam pins that would crack and break after 100 to 300 rds.

October 30, 2006, 01:18 PM
Sounds like it fired out of battery!

That and a barrel obstruction of some kind would be my 2 gueses.

James K
October 30, 2006, 08:34 PM
Thanks, Alakar. I had not heard of that happening but the result would certainly be as described, and that condition would wait until the trigger was pulled.

Of course, the same thing would happen if the rifle were assembled without the cam pin, but Capt_Vin had fired a number of rounds so that could not have been the problem. (In fact, getting the bolt to close without the cam pin is surprisingly difficult.)

I hope we can get some definitive answers from the "autopsy."


October 30, 2006, 08:38 PM

I like the broken cam pin theory. Can you look to verify it one way or another? Since you measure your loaded rounds, it seems unlikely you would have had a primer high enough to cause a slam-fire ahead of the bolts locking, but it's still a theoretical possibility and the only other cause of an unlocked discharge that occurs to me, assuming you have no lug damage.

The dings in the case necks are probably just a bump occurring on ejection. Putting a serious dent through a neck and into the bullet on chambering seems unlikely. The force required would probably cause a jam, though I have seen bullets tipped severely enough to bend a case neck because they attempted to chamber from an extreme angle. This is possible to do if you don't use a SLED for single loading, but not likely to occur regularly or to produce the same exact damage each time. Moreover, a Lee Factory Crimp die for high power cartridges puts a circumferential neck and bullet indentation intentionally into each round, and these blow open just fine. So, it isn’t likely a dented neck and bullet could be the cause of a pressure event like you described.

I didn’t notice your loading routine including a comparative visual check of powder level in your cases after charging them. Since you are weighing each charge, you may think it unnecessary? But, gremlins abound, so it is always a good idea to have the charged cases in a loading tray so you can do the flashlight once-over to be doubly sure they look the same.

I would be careful about the air nozzle you use to blow out cases. Every compressor I’ve ever had would shoot a bit of moisture and oil from time to time; usually accumulated in the short hose between the nozzle and coalescing-type water filter. It takes a powered chilling condenser filter to really dry compressed air out. A drop of wet oil that contaminated a portion of the powder might result in unexpected effects. Let us know about whether you had any lug damage?


Tim R
November 3, 2006, 03:11 AM
Unless the firing pin is protruding (due to breakage), it is impossible to get an AR-15 to fire without being locked. And if the firing pin is protruding, the rifle will fire as the bolt closes; it won't wait until the trigger is pulled. I think some more analysis is needed.

Hate to argue but the AR has a free floating firing pin. Remove a chambered but not fired round and you will find the primer will have a "dimple" on it from the firing pin. A high primer could fire out of battery.

The way I read the org posters story is he loaded and then took aim. I wonder if there wasn't something left over from cleaning.

November 7, 2006, 11:39 PM
Well, we have solved the mystery. I had a certified gunsmith who is very familiar with ARs look at the remains and his conclusion is that my lower reciever had a stress crack in it just in front of where the magazine catch is and the repeat pressures from shooting finally caused the thing to blow. I questioned this theroy until he showed me what led him to this "existing crack" idea. The edges of the crack, along where the piece broke off, had more "burn" to it than the rest. I don't wanna call it rust, so to speak, but by looking closely at it with a magnifying glass, you can see by color difference, what was old and what was new damage. He also said I had a stress crack in the right side of the lower where the front pivot pin slides in. He thinks that it would have gone sooner or later. He told me, just be thankful it didn't cause more injury that just to my wallet. And I am.

As far as my insurance goes, we sat down with our agent (who is also a friend of my wife's husband) and he explained that because of our the way policy is written, it will cover the replacement, but.........it is gonna jack the rates up 10%/year. I am still deciding, but on the bright side, I ordered my new AR and should have it in a few days. It's a DPMS with a few modifications (barrel swap, trigger change). Price wasn't that bad, below $900.00. Hopefully, this one will outlive me, LOL!

November 8, 2006, 12:10 AM
wife's husband


November 8, 2006, 01:03 AM
venison ~

I caught that too and had to read it four times before I figured out he probably meant, "the husband of a friend of my wife." :p


November 8, 2006, 06:58 AM
Well Capt,

I'm certainly not a certified gunsmith, just a guy who likes to assemble and shoot AR's, but I fail to see how a crack in the lower could lead to an explosion. As I see it, once the bolt locks into the barrel extension, the lower is irrelevant to the firing, other than to control the hammer. I've been following this thread and I tend to believe, as suggested above, the cam failed and the rifle fired out of battery. The lower may well have been previously cracked, but I do not think it caused the kaboom.

November 8, 2006, 09:46 AM
I don't think that it would be possible for a stress crack in the lower to cause a kaboom like the one you are describing. Just as stated above the upper reciver and barell take all of the pressure of the round being fired. I believe it was a broken cam pin. When you say you load one at a time do you fire one locking the mag back then load one in the chamber and hit the bolt release letting the bolt slam into the chambered round? Doing this over and over would cause the pin to break under the stress. The best way to load one at a time is load the mag and let the bolt feed the round from the mag.

November 8, 2006, 12:50 PM
I can't offer any theories, so I won't, but I do have a couple of observations.

1) I doubt that a stress-crack in the lower caused a KABOOM! As has been said, the AR locks up completely on the upper. Actually, the barrel, barrel extension and bolt all take the brunt of the force of firing. The Upper and lower just kind of hold all the parts together so they work.

2) I doubt that it was continuous single loading placing abnormal strain on parts. Highpower shooters shoot their ARs as single-shots probably 70-80% of the time, and I don't hear them talking about having abnormal rates of cam pin failures.

And for the record, I have seen a case come out of one AR-15 that looked as though it somehow fired out of battery. Primer popped out, case head bulged, blackened and torn up. The shooter never realized he had had a problem and finished the magazine without a hitch. That rifle is STILL shooting, 11 years later.

Just glad you or somebody else didn't get hurt!

November 8, 2006, 01:46 PM
Well this begs the question - who's your insurance company? Thats pretty decent policy. Is it just for firearms or is it part of the household insurance?

November 10, 2006, 10:42 PM
can you take a picture of the parts

Cal 50
November 12, 2006, 06:50 PM
Any cracks in the lower receiver could never lead to a blow up as described.
The entire lock up system is contained in the upper receiver. Was the cam pin noted as being sheared off under the flat part. That would surely cause the rifle to be able to go off without the bolt being properly rotated into battery.
If the rifle didn't fire immediatly upon going into battery it could not be caused by a high primer. A case head separation also could cause this kind of damage. Was the case head intact. Were there any telltale signs of high pressure noted on the case head. ie: case expanded at the web,shiny spot caused by the case flowing back into the ejector opening,cratered primer,etc.

I believe that I would also find a more qualified GUNSMITH that knows more about an AR type rifle that that gunsmith. His observations are a bit on the shakey side.

November 12, 2006, 07:00 PM
Agreed. That gunsmith does not know what he talking about if he says a crack in the lower caused the bolt to fail to lock in the barrel extension.

November 12, 2006, 07:33 PM
Please take a picture !:) :)

44 AMP
November 19, 2006, 12:09 AM
Symptoms described indicate firing out of battery. Cam pin seems the most likely reason. Good pictures would help a lot. Powder residue and burns have nothing to due with the lower reciever. Perhaps you were mistaken? Your gunsmith might be showing you the cracks in the lower as a problem, but they are not what caused a failure in the chamber area. If he says lower reciever cracks are why your gun went ka-boom, he is wrong.

A catastrophic failure of the lower reciever could result in the gun falling apart, or the bolt carrier flying out the back if the buffer suddenly "went away". There is no way it could have an effect at the chamber.

Why your gun fired out of battery, is still a cause for speculation, especially if it happened exactly as you describe. If you are certain there could be no error in the ammo, and that the rifle did not fire on closing, then it is most perplexing.

Detail photos of the interior parts would be of tremendous help in determining exactly what happened.

November 19, 2006, 12:31 AM
First, there is NO way that any damage to the lower receiver would cause your rifle to blow. As an earlier poster mentioned, the entire firing cycle is contained in the upper receiver. The only thing the lower does is to hold the hammer, trigger, disconnector, pistol grip, stock and buffer into a cohesive unit. You can fire an AR15/M16 with the upper and lower completely separated--I would not recommend it though, because the bolt carrier group will come roaring out of the back of the upper at a high rate of speed. (Don't ask me how I know....:eek: )

At any rate, what another poster mentioned seems to be the likely case.

First of all, how do you single load?

If you load from a magazine or SLED, the culprit is definitely overpressure--caused from the act of chambering the round pushing the bullet deeper in the case, and causing excess pressure.

While at the range, I was firing my AR when I noticed the bolt locking up about halfway through the extraction phase. I got it open, and noted that the extracted case was almost welded (!) to the bolt face. It literally looked like a .223 belted magnum case--the case web had swelled and swaged out.

Before that, I had an instance where a round had hung up upon chambering. Upon extraction of that round, I noted that the bullet had been jammed back into the case completely. I failed to heed that warning sign.

The cure for the overpressure round is to ensure that you crimp each and every round that is to be fired in a semiautomatic firearm.

For this, I highly recommend the Lee Factory Crimp die. Case neck length (while still important) is not critical; the die will apply the same crimp, over and over again. I have heard tales where this die will affect the accuracy of the loaded round--I have not found this to be the case.

Get the crimp die, chalk this one up to experience, and shoot well!

(And send your "gunsmith" friend back to school. :) )

Daniel BOON
November 24, 2006, 12:38 PM
I just quit reloading for my ar bushmaster; its tedious, and accuracy isn't any better than with factory ammo. I think I'll save my once fired brass, and trade it off for factory loaded.

November 24, 2006, 01:18 PM
I just read this whole thread, and then scanned over it again- and I still don't know which particular 'premium' winchester powder you were loading. 748? 760? Forgive me if I missed it.

I have seen 2 AR's and one FAL let go in the manner you describe, and all three were at LE range quals. In all three cases the individual shooters had supplied their own ammo. Both the AR's were with small-outfit commercial reloads, and the FAL blew with Radway milsurp. In each case it was a blown casehead, which signifies excessive headspace, off-the-scale presure, or 'bad' brass- meaning weak in the casehead, due to excessive reloading, or manufacturing gremlins. I did read that you had loaded it only once, so I got that.

Bullet setback can cause exactly the pressure spike necessary to blow a gun- and despite your rather lengthy checklist, I did not see where you crimped the bullets at the end of the loading process. I'll vote with those who nixed the idea that a cracked lower would result in a blown upper. The lower has nothing to do with the lockup of the bolt lugs to the barrel.

No Sir, you had a pressure problem here and my vote goes to bullet setback, due to lack of a crimp. There is a good reason why military bullets have cannelures in them, and why military loads have the bullets essentially laquered into the case. My suggestion is that you skip the step of each completed cartridge will being "weighed to again ensure uniformity"- and get yourself a Lee Factory Crimp Die, to apply liberally in its place.

Sorry about your rifle, and I'm not trying to be a wiseass. I have been standing within 5 feet of three rifles that 'let go' and it is an attention getter. There are ways to prevent them, and it sound like you had gone to great lengths to do just that. Adding a firm crimp is the one thing I didn't see, and IMO the one thing that got you.

Good luck with your future reloading efforts.

November 24, 2006, 02:19 PM
The instance that started this thread is very possibly the result of a cam pin failure. Cam pin failures can occur, resulting in out-of-battery firings. I have personally seen four such catastrophic failures in both M16s and M4s, and have heard of at least a dozen others in military service, some of which involved nearly new weapons. The outcome is usually a fully separated case, with the front half left in the chamber, but not always. Sometimes the case is just blown out at the base, but not completely separated. Typically, there is no damage to the bolt lugs. The cam pin is separated completely at the firing pin hole, and the gas key on the bolt carrier is bent upward several degrees from impact of the cam pin head moving vertically. There is never damage to the firing pin, but there may be some damage to the cam pin slot in the bolt carrier. The cam pin hole at the top of the bolt is usually enlarged. The extractor claw may or may not be broken off. In most cases, the shooter reports that he (and in two cases, she) actually pulled the trigger before the "KaBoom" and there was no evidence of a "Slamfire." In two of the incidentss I was able to measure the chamber throat diameter, which was within specs. In no case am I aware of any injury to the shooter.

I personally did a test firing of a junk M16 without a cam pin in place, and the results were exactly as reported above. This is strong evidence that the cam pin can fail. I have no idea as to the possible cause(s) of such failures, however. I have personally examined, under high magnification, hundreds of used cam pins without finding evidence of fracture. However, a significant percentage (20-30%) of the cam pins examined showed severe pitting, especially around the firing pin hole. Having thought about this a great deal, I can conclude only that such incidents cannot be attributed to anything other than cam pin failure.

If anyone can shed more light on this phenomenon, I'm sure many would like to know.

James K
November 24, 2006, 02:37 PM
So we have two intelligent, well informed people who have witnessed similar failures. One says categorically, absolutely, that it is due to deep seated bullets. The other says categorically, absolutely, that it is due to cam pin failure.

As I have said, I believe that the latter was the cause of the failure, since high pressure alone won't act the way described. But it is interesting that the same report can produce such widely different analyses.


November 24, 2006, 03:28 PM
So we have two intelligent, well informed people who have witnessed similar failures. One says categorically, absolutely, that it is due to deep seated bullets. The other says categorically, absolutely, that it is due to cam pin failure.

As I have said, I believe that the latter was the cause of the failure, since high pressure alone won't act the way described. But it is interesting that the same report can produce such widely different analyses.

Jim Keenan

I said it was a pressure problem, Jim- and my 'vote' went for deep-seated bullets. I think your classifying that as my saying it was "categorically, absolutely, that it is due to deep seated bullets" is a little beyond that.

I am basing the pressure diagnosis on the fact that the bullet made it halfway down the pipe... pressure obviously spiked catastrophically early in it's travels (travails?) and the brass couldn't contain it anymore. It had produced a good head of steam to wreak all that havoc, at the point that it did fail.

Based on the author's omission of any crimping operation, in his very detailed description of his loading process, I will go on paper as calling "setback" the most likely cause. I won't pretend that I could conclusively diagnose it if I had the remains in front of me- although I'd really like to see it. Especially the remains if the case head...if the primer pocket was enlarged or blown, and/or the headstamp 'blurred' by contact with the boltface- pressure just about has to be the culprit.

I will add however that I am still learning something new every day- and today is certainly no different.

Take care- and thank you for the compliment.

James K
November 25, 2006, 05:34 PM
My apology for the attempt at humor by using the terms "categorically" and "absolutely."

I agree that no one will know until the poster either provides more info and pictures, or until someone with more knowledge looks at the rifle. The fact is that few gunsmiths have ever seen a catastrophic failure (a tribute, I guess, to modern arms makers) and have no idea how to analyze one.

I accept that under some circumstances high pressure can result from bullet setback, even though my own experiments show that the pressure rise is nowhere near as great as sometimes claimed. It could be high enough to enlarge a primer pocket or blur a headstamp, but I don't think it would dissolve a case head as high pressure could in, say, an M1903. The AR-15 is pretty well protected against that kind of disaster.

Of course, the bolt lugs could shear under extremely high pressure, but I just don't think bullet setback could generate the hundreds of thousands of pounds needed to do that! Also, I think the poster would have mentioned it if the bolt lugs were gone.

My vote is still with a broken cam pin. That is not ruled out by the bullet having moved down the barrel. Even if the bolt head were not locked, the inertia of the bolt alone would retain enough pressure to move the bullet.


November 25, 2006, 07:07 PM
You may well be correct Mr. Keenan, and I figured you were yanking my chain a little;) No problem.

On 1903's...I had a low-numbered sporterized Springfield back when I was 16, and dinosaurs roamed the earth. I was long on P&V and short on caution in those days, and utterly ignorant of the problems inherent in that batch. A buddy had a loader and we ran quite a number of stout reloads through that old gun. Mine must have been made on a day when the light was just right, because it stood the strain of a couple of teenagers with a loading press.

I also agree regarding the improved safety margins built into modern arms. Out of the three blown rifles I mentioned, no one was significantly injured. That alone says a lot.

I remain interested in hearing further expert diagnosis of the problem with the subject gun.

Harry Bonar
November 26, 2006, 10:48 AM
Dear Sir:
I know of no quality made firearm that "blows-up" with-out some human intervention! If the cartridges were "handloaded" then I think there is the problem.
Harry B.

November 29, 2006, 10:10 PM
One can blame these incidents on ammunition, but such does not stand up under scrutiny. First, the M16 (military version) can easily withstand chamber pressures well in excess of 80KPSI without damage (when fired with the bolt head lugs in place). I have information directly from Colt to this effect. They got such pressures by the use of pistol-type propellants, as it is absolutely impossible to force enough of the types of propellants normally used in the 5.56mm into the case to reach such chamber pressures. If you wish, pull the bullet on a round and see the propellant level for yourself. The sase is nearly full. Second, I have yet to see an incident of this nature in which either the lugs on the bolt or in the barrel extension were damaged - a certain indication of an out-of-battery firing condition. Also, in every case, the cam pin was fractured and separated at the thin section at the firing pin hole. I consider the cam pin design to be suspect at best, because the metal cross-sectional area at this point is only 0.027 square inches, about 1/3rd that of the pin body itself. I've often thought that a beefier cam pin or a smaller firing pin hole in the cam pin would be better.

I wish I had all the answers, but I don't. Probably having seen more of these incidents than anyone else in this thread, or maybe everyone combined, I know the symptoms well. However, I can't explain the reasons for the probable cam pin failures I have witnessed.

By the way - I failed to mention in my earlier posting that there was clearly a firing pin indentation in the primer in every case I know of, and that supports the lnvolved firers' stories that they actually pulled the trigger before the incident occurred. Let's keep this thread going, maybe someone has the answer.