OP edited to say Armalite BCG in DPMS upper. I don't think that's what made this happen. If it is actually an Armalite carrier, it's an old one. The newer ones are notched for FA use. The head of the cam pin doesn't look right to me either.
6.5 upper build went kaboom
- Thread starter matty86suk
- Start date
OP edited to say Armalite BCG in DPMS upper. I don't think that's what made this happen. If it is actually an Armalite carrier, it's an old one. The newer ones are notched for FA use. The head of the cam pin doesn't look right to me either.
It sounds like the clown at the gun show is the culprit. Mixing bolts and carriers between the two types has always been a recipe for disaster.
Sorry but it is the builder who is responsible, he made a mistake and luckily only some parts were damaged.
Not the first time parts have been mixed up or labeled incorrectly.
Not the first time parts have been mixed up or labeled incorrectly.
So you'd expect to buy Armalite parts in a Brownell's wrapper? It LOOKS like an Armalite carrier, an old one. There is no firing pin spring in any of the photos. I agree that ultimately as the builder you're responsible but I certainly wouldn't buy anything from that seller again.
I noticed that as well... and looked quite a bit for that style cam pin... I "think" I remember one sold like that... it was shaped like a football on the top.
I take full responsibility for this disaster. I paid the price for trying to save a buck, save some time and not fully understanding what I was doing. I posted here to help me figure out what went wrong and I have been completely up front as a reference, and hopefully a lesson for the community.
I hope the biggest thing we take away, as a lesson, is what actually happened when we know what actually happened. Yeah, that way we wont mix and match incompatible parts if that’s the issue here.
However, I don't want to see “incompatible parts” as the reason if something else is at fault and those behind a part continues to have, and put bad parts, out on the market.
I haven't seen definitive proof that incompatible parts was the reason.
Last edited:
Fully agree. While it might be convenient to blame the Armalite BCG... we still don't have enough info to come to a explanation.
For the OP... first, I forgot to say, I am glad you are ok.
@matty86suk
Did you disassemble the BCG after the kaboom... specifically the Firing pin, and FP retaining pin ?
Also the extractor ?
I am curious where those 2 retaining pins are. Again the FP retaining pin ( cotter key ) and the extractor pin.
Also, can we see if pic's of the left hand side of the BCG.. and at least one, where the FP retaining pin sits... I can't quite tell if the pin is still in there.
@matty86suk
Did you disassemble the BCG after the kaboom... specifically the Firing pin, and FP retaining pin ?
Also the extractor ?
I am curious where those 2 retaining pins are. Again the FP retaining pin ( cotter key ) and the extractor pin.
Also, can we see if pic's of the left hand side of the BCG.. and at least one, where the FP retaining pin sits... I can't quite tell if the pin is still in there.
That's why I seriously doubt what happened was simply because oh, Armalite in DPMS/KAC. GAP10s used to use Armalite and Seekins I believe. The JP low mass .308 BCG I briefly owned appeared to have an identical bolt to my Armalite. But I didn't mix and match parts in the BCGs. A long time ago I swapped BCGs between a Panther .308 and my AR-10. I know they both cycled fine empty but can't remember if I checked headspace. Either way, there was no way I was going to fire either in that configuration.
I have done a .308 and .260 using Armalite BCGs which have the benefit of the smaller firing pin diameter so no need for "high pressure" bolts and they have hundreds of rounds without a problem. After a long conversation with someone who used to sell Craddock built barrels, this is an old wives tale. If it wasn't you'd be specifying what barrel extension to buy or barrel to buy. I'd love to hear a conclusive answer on this.
I think barrels being sold as DPMS or Armalite specific has more to do with the fact that the gas system lengths may vary, mid-length certainly does. When I put a "DPMS" mid length Rock Creek on my AR-10, I had to buy a new gas tube as it is the same as an AR15 while Armalite has a proprietary tube length.
The ammo until kaboom was ejecting at 6 o'clock and landing 2 - 3 feet away, certainly doesn't sound over pressure. I wouldn't think you'd get a case mixed with pistol powder like the most famous AR15 kaboom I've seen from a company as large as Federal. But it's a possibility. There is some similarity in damage excluding this broke the barrel extension. This was commercial ammo from supplier that was previously making handgun ammo. The mixture was confirmed in rounds remaining that the shooter had. Disregard the speculation on these sites, posting just for the photos.
AR-15 Kaboom – Why I Don’t Reload – Everyday No Days Off
www.everydaynodaysoff.com
Duplex Powder Loading Causes Catastrophic AR15 Kaboom « Daily Bulletin
Thinking of combining rifle and pistol powder in a blended duplex load? Well think again. If you want to keep all your fingers, stick with factory powders and established loads at safe pressures. Here's what can happen with a duplex load composed of both rifle and pistol powders.
Misaligned or index pin problem. It would seem for that to happen the barrel wasn't torqued to the extension properly. At least this could be tested now. I was told previously the index pin isn't holding anything, not like it's countersunk into the barrel.
Since I've only ever been around bolt gun barrels being chambered I never understood how this is done. I would believe you simply thread the barrel and attach the extension, then cut the chamber while checking headspace with a bolt. I don't know what's involved about installing the index pin other than it should line up with the gas port.
Forgot who said it, but carrier broke unnoticed on 4th shot and lugs didn't lock for final. Hard to prove but why I'm hard on the seller. An 8620 carrier ought to last longer than the "100 rounds" it had on it. When it looks like the BCG was also missing parts, like the spring on the firing pin, it just looks like it wasn't really cared for to me. And maybe rode really hard. Might be a lesson here about new vs. used parts.
Ultimately it sucks for the OP but I'm just glad no serious injuries occurred. Don't hold the bottom of the mag is another lesson there.
Last edited:
That's why I seriously doubt what happened was simply because oh, Armalite in DPMS/KAC. GAP10s used to use Armalite and Seekins I believe. The JP low mass .308 BCG I briefly owned appeared to have an identical bolt to my Armalite. But I didn't mix and match parts in the BCGs. A long time ago I swapped BCGs between a Panther .308 and my AR-10. I know they both cycled fine empty but can't remember if I checked headspace. Either way, there was no way I was going to fire either in that configuration.
I have done a .308 and .260 using Armalite BCGs which have the benefit of the smaller firing pin diameter so no need for "high pressure" bolts and they have hundreds of rounds without a problem. After a long conversation with someone who used to sell Craddock built barrels, this is an old wives tale. If it wasn't you'd be specifying what barrel extension to buy or barrel to buy. I'd love to hear a conclusive answer on this.
I think barrels being sold as DPMS or Armalite specific has more to do with the fact that the gas system lengths may vary, mid-length certainly does. When I put a "DPMS" mid length Rock Creek on my AR-10, I had to buy a new gas tube as it is the same as an AR15 while Armalite has a proprietary tube length.
The ammo until kaboom was ejecting at 6 o'clock and landing 2 - 3 feet away, certainly doesn't sound over pressure. I wouldn't think you'd get a case mixed with pistol powder like the most famous AR15 kaboom I've seen from a company as large as Federal. But it's a possibility. There is some similarity in damage excluding this broke the barrel extension. This was commercial ammo from supplier that was previously making handgun ammo. The mixture was confirmed in rounds remaining that the shooter had. Disregard the speculation on these sites, posting just for the photos.
AR-15 Kaboom – Why I Don’t Reload – Everyday No Days Off
www.everydaynodaysoff.com
Duplex Powder Loading Causes Catastrophic AR15 Kaboom « Daily Bulletin
Thinking of combining rifle and pistol powder in a blended duplex load? Well think again. If you want to keep all your fingers, stick with factory powders and established loads at safe pressures. Here's what can happen with a duplex load composed of both rifle and pistol powders.bulletin.accurateshooter.com
Misaligned or index pin problem. It would seem for that to happen the barrel wasn't torqued to the extension properly. At least this could be tested now. I was told previously the index pin isn't holding anything, not like it's countersunk into the barrel.
Since I've only ever been around bolt gun barrels being chambered I never understood how this is done. I would believe you simply thread the barrel and attach the extension, then cut the chamber while checking headspace with a bolt. I don't know what's involved about installing the index pin other than it should line up with the gas port.
Forgot who said it, but carrier broke unnoticed on 4th shot and lugs didn't lock for final. Hard to prove but why I'm hard on the seller. An 8620 carrier ought to last longer than the "100 rounds" it had on it. When it looks like the BCG was also missing parts, like the spring on the firing pin, it just looks like it wasn't really cared for to me. And maybe rode really hard. Might be a lesson here about new vs. used parts.
Ultimately it sucks for the OP but I'm just glad no serious injuries occurred. Don't hold the bottom of the mag is another lesson there.
If you actually sit down and check all the dimensions on the Armalite and DPMS bolt carriers you find a variety of different measurements... in places that may or not matter.. but they are there.
Stand a Armalite 308 BCG ( on the bolt face ) next to a DPMS pattern one... you will see the bolt carriers face is longer, so interchanging those 9 The bolt carrier ) might make quite a bit of difference, since the cam pin might not travel the same distance ... and the gas key on a DPMS is further forward as well... not just a few thousands.. quite a bit actually.
The cam pin path is also at a different position between the 2... again more then you would realize. about 20/100ths difference
Even the Bolt carrier face to the bolt face 9 when fully locked is 14/100ths different.
Even the bolt face to gas key difference is quite a bit... 40/100ths
Combine all that with a lack of "Mil-Spec" guideline... and maybe the Seekins upper tolerance stacked badly.
Basically I am saying while the bolts themselves may be close enough... there are distinct differences on the bolt carrier dimensions.
And those differences might have contributed to the failure.
As for the index pin... it is press fit into the receiver extension , directly behind the RE shoulder collar. And interacts with the upper receiver notch at the threads.
FWIW, I have fired a AR15 5.56 with a loose USGI style barrel nut, it was hand tight, and was being held in position by the gas tube.
It had no issues firing... but precision was dismal.
I don't know what handguard was used by the OP... but most all of the FF tubes clamp onto the simple circular barrel nut... I would have figured the OP would have noticed movement of the handguard / FF tube.
I am wondering if the bolt carrier was already cracked.. it was purchased used at a Fun Show.
Similar threads
