Here is a second BCG in the exact position as your 'third position'. It is brand new in the box from Lantac.
The firing pin goes far enough out on this one too. It will definitely contact a primer in that position.
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Here is a second BCG in the exact position as your 'third position'. It is brand new in the box from Lantac.
The firing pin goes far enough out on this one too. It will definitely contact a primer in that position.
You are missing the point. Your bolt is rotated (not cam pin location) meaning it's locked. The bolt cannot rotate until it's locked into the extension. Now move the bolt until it's unlocked and see if the firing pin protrudes.
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The bolt has to rotate a lot for this to even happen. The bolt can't rotate until it's in the extension. If it rotates as much as your picture while it's in the extension then explain how it's an OOB condition?
That's from the floating firing pin and it happens after it's locked because it can't reach until it locks. Because the BCG stops it's forward travel and the firing pin has nothing to stop it, inertia carries it and it hits the primer. It doesn't carry enough energy to set off the primer but with the right combo of parts, you can cause a slam fire (See recent thread on slamfires). But a slamfires is not an OOB discharge.Just out of curiosity, all my ARs will leave a witness mark on the primer of a chambered but unfired round, so when is this happening? After rotation? It would seem more logical for it to protrude as the bolt stops at the extension before or as it starts to rotate? Just an uninformed thought !
You said it was the first round fired? The other 9 were pulled and were on the money? Your procedures include checking for double charges? You're sure there was wasn't a bullet lodged in the barrel/suppressor from a previous outing where subs were used? Are you sure you have H110 in your H110 bottle? In any case, I'd pour this bottle out across the backyard if you can't find a plausible explanation. I'm glad you are ok.
Of course the firing pin can protrude when the bolt is fully compressed into the bcg. This is the fully locked position and is equivalent to “position 2” in my previous post.
Take your bcg and push the bolt completely in. Now, while putting some “anti-rotation” torque on the bolt and bolt carrier, pull the bolt out. It should move 2-3mm before it begins to attempt to rotate. This is “position 3” in my previous post, and the condition of the bolt/carrier the instant it is fully locked. If you push the firing pin forward, you will note that it does not protrude through the bolt face. The carrier must move, minimally, another mm before the pin protrudes.
I pulled a bcg from another gun, just to confirm similar function, and they bothe function the same.
Further, look at the cam pin track. Going from fully open to fully locked, you wil I’ll note that the track begins with an angle cut, relative to the direction of bcg travel, but ends with a few mm that are directly parallel to that direction of travel. The angled portion rotates the bolt in and out of the locked position. The parallel portion moves the bolt carrier forward enough that the pin can hit the primer. But, this action occurs after the bolt is locked. If your bolt/carriers do not function this way, I am positing that they are faulty. But, I strongly suspect there is merely a misunderstanding.
I've already explained that. But I will do it again.
The brass is for example to fat in the neck so it essentially gets jammed into the chamber. The momentum of the carrier attempts to keep on going forward and thus twist the bolt to a full lock position. Except it cannot. The lugs on the bolt and the lugs on the barrel extension have lateral friction hence it slows down the firing sequence even more. Then when the lugs sneak forward just enough to alleviate the friction between the barrel lugs and the bolt lugs. Hence when the firing pin gets hit it was only in a partially locked position...
As I have said earlier, the sequence of events gets all messed up because of the delay...If the round gets stuck far enough out...you get click no bang. However if it happens right in that sweet spot this is the result.
Been following along, and appreciate your visual cues. My apologies for using your post to make my statement regarding this opinion, and the others like it.
OOB discharge and hammer follow (another cause of oob discharge), is literally THE reason for the auto sear. To create proper timing and "prevent out of battery discharge".
Maybe those are just different though
This is position 1 from my previous post. This is all the way seated.
This is position 2. On both bolt carrier groups (the Radian and the Lantac) the firing pin is protruding while they are in position 2.
This is the Radian in what I called 'position 2' or what you called 'position 3'.
This is the Lantac.
In position 2 the bolt lugs have full engagement. What is your point?
I'm sure there was no obstruction. As to my procedure, never had a problem before but I'm only human. I have a powder cop on the progressive press but do I look at every single case? I'd hope so but unlikely.
Agree 100%... No way in hell that load caused that. I run those same bullets, and used to run H110, and 10.5 was no issue in mine. It was supersonic, so I backed it down, but it wasn't even remotely too hot of a load for the gun.
My guess is he either had a squib load and had a bullet stuck in the barrel, or something stuck in the barrel, or his powder charger was WAY off calibration and dumped a ridiculous amount of powder, or like you said, OoB explosion. Or, he used the wrong powder, or something... But there's no way even 11 grains of H110 with that bullet would cause that.
Usually you see an incident like this happen when someone loads a .300 BLK round in a .223 magazine by accident... Because .300 BLK will actually chamber and FIRE in a .223/5.56 chamber, but a .223/5.56 will not fit in a .300 BLK chamber.
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Read slowly this time please.
There are two forces. Forward momentum and rotational force. Both of those combined together create a 'binding effect' between the bolt lugs and the lugs in the extension. Because the cartridge (in this example) is in essence stuck, it's putting force on the bolt prematurely. Hence the bolt is trying to rotate prematurely but it is basically rubbing laterally against the lugs in the extension. The milisecond it gets beyond the inside edge of the extension lugs it tries to snap into place as one of the frictional points is eliminated. The second it gets to position 2 the primer gets struck. Because there is also forward momentum drag, only a partial lock up happens when the kaboom goes off.
What don't you understand about position 2 having full lug engagement? It's not partial. It's full.
I'm done. You don't know how an AR functions and you aren't interested in learning from someone who does. Good luck!
I am totally interested in learning from someone that knows... unfortunately that's not you.
The M231 FPW is an example of how a firing pin held in the forward position, relying on the bolt to rotate which then allows the FP to protrude to fire the cartridge, negates most OOB arguments. Same bolt, FP, cam pin as an M16 or AR-15.
Hard to get a photo right up inside the chamber but there appears to be brass transferred to just before the rifling (is that called the forcing cone? I forget) but whether that's from a long case or a result of the failure, I've no idea. Nicely fireformed case anyway 
I'm just throwing this out there after seeing the remains of your brass. These pics are of once fired/processed LC 308 cases from TOP BRASS, bought way back in the early 20teens. These have been reloaded/fired one time. The failures are in the absolute strongest part of the brass, and are failures of the brass itself, not case head separation. One of the rounds blew the Pmag out of the gun and rendered the mag useless due to the mag catch groove being stripped out of the plastic body. I think these could have easily been more catastrophic.
After realizing the brass was at fault, I used a light to inspect the interior of the remaining cases I hadn't yet loaded. I found approximately 45-50 more cases (out of about 800 cases) with the interior cracks around the flash hole. (These were still in a sealed bag, unused) I finally forced myself to go ahead and cull every LC case I had from that lot. I still have probably 1200 or so rounds of this brass that I had already loaded that I have yet to pull the bullets and salvage the components. The headstamps spanned several years, so I can't say it's isolated to 1 lot from the factory. I don't see how Top Brass could have damaged it in this way in the processing. Could it be possible you got ahold of some brass with the same damage/defect? Just another remote possibility to consider.
ETA: I did find similar case failure on some other forums, but in each case it was LC 308. No other caliber
Attachments
That's really interesting. The 300aac I bought from them was pretty poor. Crimps not removed, split necks, serious dents and several with ejector damage bad enough to stop them fitting into a shell holder.
I really need to get more organized and keep track of my brass! Thanks for your input.
Do you still have some of that brass? If so use a small flashlight and inspect the interior around the flash hole for cracks/deformities. If you find any, that would lead me more toward Top Brass being the problem rather than LC. I did not even try to contact them because I didn't start using the brass until about 5-6 years after I bought it. I sold it to the local scrap yard as clean brass. I replaced it with commercial brass bought somewhere else, non LC. I doubt LC even makes 300aac.
I don't recall what the headstamps were but I'll go through my loaded rounds and see if I can figure them out.
This is from Midsouth Shooters Supply where I bought them from. I too doubt the military use 300aac so maybe they're converted 5.56 but they didn't look freshly made.
Specifications & Features:
- Once Fired Military Brass
- 100% Fully Processed & Reconditioned
- Mixed Military Headstamps
- Deprimed
- Cleaned
- Full-length Sized and Trimmed
Note:Assorted Headstamps may vary from package to package.
So with everything that has been posted here is my best guess at what might have happened.
Case was converted from once fired .223 case. Here is a list of case head stamps that are not suitable for conversion to 300 BO:
"Thick neck wall, bad without neck turning:
ATI - 0.015" [Note 3]
CBC - 0.014/0.015"
CJ6 - 0.015"
DNL - 0.016"
FNM - 0.016" [Note 3]
FRONTIER - 0.015"
GECO - 0.015/0.016"
Hot Shot - 0.014" [Note 3]
HRTRS ( Herters?) - 0.017"
ICC - Reported as bad
IK03 - 0.015" [Note 4]
IMI - 0.015" [Note 4]
KFA .223 REM - 0.015"-0.019"
MKE13 - Anecdotally reported as troublesome
MPA - 0.015"
NPA - [Note 3]
PMC (old headstamp) - 0.015"
PMP - 0.015"
PPU - 0.014/0.015" [Note 3]
RORG - 0.015"
RWS - 0.014-0.015"
S&B - 0.015/0.017"
Wolf Brass .223 - 0.014"
General notes:
There's no consistent difference between "5.56" and "223" when it comes to brass."
Now minimum chamber is 0.335" and maximum case neck is 0.334". That means zero clearance in chamber would be 0.355" minus 0.308 equals 0.027" or 0.135" case neck thickness, anything greater would be a interference press fit.
Even if you can't determine the case headstamp you can measure the neck thickness of the piece of brass pulled from the chamber. That number will tell you if there was any neck clearance for the loaded round or the round was pressed into the chamber and locking the bullet in the case. If it was locked into the case that would create excess chamber pressure above the max 55,000 psi SAAMI number.
The only place the case is not surrounded is between the barrel and bolt. Excess pressure would cause case separation. Bolt would be driven back against the inside barrel extension and deform the bolt and barrel extension as the pressure drives the carrier rearward. During this the bolt is fractured, the carrier is split and resulting damage to the receivers and rounds in the magazine.
A simple oversight of not checking the neck wall thickness could have been the cause of this incident.
Case was converted from once fired .223 case. Here is a list of case head stamps that are not suitable for conversion to 300 BO:
"Thick neck wall, bad without neck turning:
ATI - 0.015" [Note 3]
CBC - 0.014/0.015"
CJ6 - 0.015"
DNL - 0.016"
FNM - 0.016" [Note 3]
FRONTIER - 0.015"
GECO - 0.015/0.016"
Hot Shot - 0.014" [Note 3]
HRTRS ( Herters?) - 0.017"
ICC - Reported as bad
IK03 - 0.015" [Note 4]
IMI - 0.015" [Note 4]
KFA .223 REM - 0.015"-0.019"
MKE13 - Anecdotally reported as troublesome
MPA - 0.015"
NPA - [Note 3]
PMC (old headstamp) - 0.015"
PMP - 0.015"
PPU - 0.014/0.015" [Note 3]
RORG - 0.015"
RWS - 0.014-0.015"
S&B - 0.015/0.017"
Wolf Brass .223 - 0.014"
General notes:
There's no consistent difference between "5.56" and "223" when it comes to brass."
Now minimum chamber is 0.335" and maximum case neck is 0.334". That means zero clearance in chamber would be 0.355" minus 0.308 equals 0.027" or 0.135" case neck thickness, anything greater would be a interference press fit.
Even if you can't determine the case headstamp you can measure the neck thickness of the piece of brass pulled from the chamber. That number will tell you if there was any neck clearance for the loaded round or the round was pressed into the chamber and locking the bullet in the case. If it was locked into the case that would create excess chamber pressure above the max 55,000 psi SAAMI number.
The only place the case is not surrounded is between the barrel and bolt. Excess pressure would cause case separation. Bolt would be driven back against the inside barrel extension and deform the bolt and barrel extension as the pressure drives the carrier rearward. During this the bolt is fractured, the carrier is split and resulting damage to the receivers and rounds in the magazine.
A simple oversight of not checking the neck wall thickness could have been the cause of this incident.
Thanks, that's good info and i have to admit, neck thickness has never been a consideration. Guess I've just been lucky with all the rounds I've reloaded to date!
the .308 and 5.56 from them is notoriously poor because they get it from ranges using clapped-out training machineguns that have chambers that should by all rights be out of service. That and then TB re-forming it using small base dies is what causes the cracking, just too much working of the brass.
as to this event, my guess is the converted brass was the culprit, leading to a locked-in state.
pretty much the entire reason I only use factory cases of the caliber I'm using, even for my wildcat (thankfully .375 raptor brass is easy-ish to get), and stick to specific brass manufacturers for specific loadings.
Show us an AR-15 BCG with the bolt in the forward telescoped position where you are able to get firing pin protrusion.
(You can’t.). It’s a mechanical impossibility due to firing pin length and bolt length plus its extended position in the carrier.
In order for the bolt to enter the extension, the bolt must be fully-forward with the cam pin in the forward position in the cam helix.
In order for the firing pin to be able to protrude, the bolt must be rotated and collapsed within the carrier, with the cam pin rotated to its rear position in the helix, as in your photo. There is no way for the BCG to be in that position unless the bolt is locked inside the extension.
He isn’t wrong. If he was, anytime someone used the forward assist, an OOB condition would occur.
By an out of spec upper.
First mistake is listening to anything that Re-re Gavin had to say. The guy is a software developer who bought his way into youtube fame. He knows less than the average drunk working at the local gun store.
Enough already. The pin cannot physically protrude from the bolt face of an in-spec carrier until the lugs are in the locked position. Every picture you’ve show of pin protrusion has been in the full locked position.
The upper isn't out of spec. I don't know how the OP's gun blew up. I can only tell you this subject has been discussed a lot over the years and OOB detonations happen. It doesn't look like that is what happened here though.
Just not on in spec ARs.
Well I'm stumped. I measured neck thickness on various brand cases and all but LC were fine. And of course, all these cases have been through this gun before except some factory Remington and Magtech that I used a few days ago in a Ruger Ranch, but I've put new Rem and Magtech through this rifle many times.
Did, for some bizarre reason, the bullet set back massively as it chambered (they are pretty long and fat), who knows but would that even cause this? That's just a small compressed load surely??
I've looked at the powder with a magnifying glass and compared to another pot of H110, they are identical.
Casing failure? Head separating ? Seems a bit violent for that but I've never had that issue.
OOB firing? I'm sorry this thread has turned into a bit of a handbag fight over that subject but I have no opinion on it , not really knowing if it's a possibility.
That just kind of leaves pistol powder being left over in the powder drop. I really don't think this is the case BUT, certainly would explain it. I 'know' it was empty so ....
and finally .... a double charge. Certainly a possibility. Although I was using a progressive, so in theory not possible, maybe I was setting up the charge weight and didn't empty the final test case before doing a loading run. Has anyone got that ballistics program that can give you the pressure of 18gn of H110 under a 220gn bullet in 300aac?
I've taken advantage of Black Friday and got a BCG, upper receiver and mag catch on the way. I have a spare new barrel in the safe anyway. I am NOT looking forward to pulling the trigger on that set up again!
Did, for some bizarre reason, the bullet set back massively as it chambered (they are pretty long and fat), who knows but would that even cause this? That's just a small compressed load surely??
I've looked at the powder with a magnifying glass and compared to another pot of H110, they are identical.
Casing failure? Head separating ? Seems a bit violent for that but I've never had that issue.
OOB firing? I'm sorry this thread has turned into a bit of a handbag fight over that subject but I have no opinion on it , not really knowing if it's a possibility.
That just kind of leaves pistol powder being left over in the powder drop. I really don't think this is the case BUT, certainly would explain it. I 'know' it was empty so ....
and finally .... a double charge. Certainly a possibility. Although I was using a progressive, so in theory not possible, maybe I was setting up the charge weight and didn't empty the final test case before doing a loading run. Has anyone got that ballistics program that can give you the pressure of 18gn of H110 under a 220gn bullet in 300aac?
I've taken advantage of Black Friday and got a BCG, upper receiver and mag catch on the way. I have a spare new barrel in the safe anyway. I am NOT looking forward to pulling the trigger on that set up again!
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Look at the pics in post 109. Already been posted.
I don't crimp any rifle ammo for any cartridge (other than straight-wall, obviously), and I've never had an issue in 10s of thousands of rounds...
Yep... It's says that we should leave the .300 BLK subs to the Alliant 300-MP and CFE-BLK.H110 is revolting because it belongs in 24 grain amounts in a 44 magnum.
Glad you are ok!!!
Happy thanksgiving!
If the bolt is fully is not fully retracted in the BCG, the pin does not protrude past the bolt face. If it does, you have an out of spec BCG.
I would not take any chances on the remaining parts. Is your sight really worth a couple hundred bucks? You can contact https://schooloftheamericanrifle.com/ and see if he would be willing to conduct a forensic examination of your rig.
I have seen many of his videos on YT, and he does not fuck around. Probably one of the most educated individuals on the AR platform that I have ever seen. Shit, he might even end up making a video about it too.
I have seen many of his videos on YT, and he does not fuck around. Probably one of the most educated individuals on the AR platform that I have ever seen. Shit, he might even end up making a video about it too.
Apparently I have two of them. One from Lantac and one from Radian that is 'out of spec'...
IDK ... that case mouth looks pretty clean to me but I am definitely not an expert.
I guess I missed this part earlier, definitely not thinking out of battery anymore ... impressive.
Even if it did protrude, the cartridge has to over come the extractor and the ejector spring to be seated deep enough in the bolt face for any FP engagement, that doesn’t happen until the cartridge is fully seated in the chamber and the bolt is rotated into battery. The case head is nowhere near the FP when the claim of the protrusion is happening.
We’ve got extractor, ejector, bolt lugs and cam pin to over come before this hypothetical can happen.
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I was specifically responding to that post. I don’t see a bolt in the extended, fully-forward position. Of all the AR-15 bolts I’ve seen since the 1980s, I’ve never seen one in that position where it’s even remotely possible to having firing pin protrusion. Fully-forward means the bolt pulled out of the carrier as far as possible in the assembled condition (cam pin installed).
You would need some really funky parts dimensions with the Firing Pin or bolt to be able to make it protrude in the extended position. This is not hard.
So I was out checking my fences at the weekend and rode past the target I was aiming at when this blew up on me. Fresh target sheet. It had a bullet hole in it! A bit lower than than I was aiming for but on target. I then realised that I had my magnetospeed on the rifle too. So I went and checked the data expecting to see a crazy velocity due to a likely double charge and …… 888 fps. Hardly fast!
So I hit the target, speed was about 100 fps lower than I was aiming for yet it blew my bolt to pieces. Now I’m even more confused!!
So I hit the target, speed was about 100 fps lower than I was aiming for yet it blew my bolt to pieces. Now I’m even more confused!!
That’s because your remaining velocity was in the rearward motion. LolSo I was out checking my fences at the weekend and rode past the target I was aiming at when this blew up on me. Fresh target sheet. It had a bullet hole in it! A bit lower than than I was aiming for but on target. I then realised that I had my magnetospeed on the rifle too. So I went and checked the data expecting to see a crazy velocity due to a likely double charge and …… 888 fps. Hardly fast!
So I hit the target, speed was about 100 fps lower than I was aiming for yet it blew my bolt to pieces. Now I’m even more confused!!
Not all the pressure created was shoving the bullet.
I read Berry's and immediately thought bullet setback.
The reason I stopped using their pistol bullets years ago. Too many undersized bullets.
The reason I stopped using their pistol bullets years ago. Too many undersized bullets.
