Guy assembles AR15 without Bolt. Here is the aftermath

[ToolAA]

Found this post on reddit r/AR15

Looks like he somehow still installed the firing pin and it stayed centered with the primer. At least enough to detonate the primer. What I don’t understand is how the BCG chambered the round without the bolt lug there to catch the rim of the case to push the cartridge from the magazine. The only thing I can think of, is that the shooter unsuccessfully tried to chamber a round by engaging the bolt, and then just manually slipped a round into the chamber through the ejection port.

Here is the link to the reddit thread. No real insight there. We’ll probably have a more insightful discussion here. Tagging [mention]clandestine [/mention] to see if he has ever seen something like this before. If not it will make a good addition to his collection of failure photos.


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[Trigger Time]

Proof that some people should not be building firearms.

 

[wilcam47]

 

[Doco Overboard]

Id like to see the rest of the system to see how well the rest of it fared out.

 

[Doctor_M]

Yikes.

 

[jrumann59]

is it real, without a bolt it will it still strip a round, but with the firing pin place it would jam or bend the firing pin because the firing pin would be getting to the chamber at about the same time as the last 20% of the cartridge. Anything is possible

 

[papnschmilees]

I love that the cam pin is installed....

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[ToolAA]

is it real, without a bolt it will it still strip a round, but with the firing pin place it would jam or bend the firing pin because the firing pin would be getting to the chamber at about the same time as the last 20% of the cartridge. Anything is possible

I don’t see how the BCG alone would chamber the round. Maybe without the bolt, the bottom edge of the BCG would hit the case head?

As for firing, that seems even more unlikely. Without the bolt to align the pin, perhaps the cam pin alone was just enough to keep it somewhat centered.

Still, with no bolt, the round could have not been fully chambered. With no bolt, the cartridge would have been pushing the pin back even before the hammer dropped. After looking closer at the mechanism I really dont see how it was chambered or fired.


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[Lafayette]

I love that the cam pin is installed....

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That’s probably what kept the firing pin centered.

This smells fishy…I think it was all on purpose.

 

[John from MD]

I love that the cam pin is installed....

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The firing pin wouldn't have stayed centered if it wasn't.

 

[4g64loser]

While I haven't seen the rest of the gun or actually tried this trick live (in some other suckers gun of course) let me toss this into the MDS piranha tank:

Cam pin is in, this keeps the firing pin relatively centered. The firing pin retainer is clearly in or the pin would have fallen out the back of the carrier.

I just stripped a carrier and tried picking up a round (carrier only, no firing pin, it's MY gun!). The round ended up out of the mag, in the chamber, when I retracted the bolt carrier. If I let it go back in, let the bolt forward, and muzzle up the gun, loaded round ends up in the carrier center bore on retraction.

Since you guys have me thinking,

Here's the bolt carrier as assembled by this idiot cam pin in the forward position.

Here's the carrier installed in the rifle the way the idiot did it.

Just for you guys, I took a piece of cleaned/annealed/sized/trimmed/chamfered/deburred PMC brass out of my stash. I took a spent primer, removed the anvil, drove the cup flat with a punch, pushed the anvil back in, and seated it in the case. I then colored the primer with a red sharpie. I placed the case in the chamber and let the bolt fly with the bolt release. You can see the firing pin impression on the primer and the transfer of red pigment on the firing pin tip.

You are all welcome. My beer got warm, my pizza needs to be nuked again and I risked my firing pin bending or breaking. But at least now we all know.

And somebody clean this gun. It's dirty.

Post pizza edit to add: if you look at the OP picture, you will see that there is unburnt powder all over the carrier. The case failed at relatively low pressure, based on this observation. I'd bet that the gun wasn't failed and that if he put it together correctly the next time it works.

 

[gforce]

Wow, just wow.

While I haven't seen the rest of the gun or actually tried this trick live (in some other suckers gun of course) let me toss this into the MDS piranha tank:

Cam pin is in, this keeps the firing pin relatively centered. The firing pin retainer is clearly in or the pin would have fallen out the back of the carrier.

I just stripped a carrier and tried picking up a round (carrier only, no firing pin, it's MY gun!). The round ended up out of the mag, in the chamber, when I retracted the bolt carrier. If I let it go back in, let the bolt forward, and muzzle up the gun, loaded round ends up in the carrier center bore on retraction.

Since you guys have me thinking, View attachment 411980
Here's the bolt carrier as assembled by this idiot cam pin in the forward position.

View attachment 411981
Here's the carrier installed in the rifle the way the idiot did it.

View attachment 411983
Just for you guys, I took a piece of cleaned/annealed/sized/trimmed/chamfered/deburred PMC brass out of my stash. I took a spent primer, removed the anvil, drove the cup flat with a punch, pushed the anvil back in, and seated it in the case. I then colored the primer with a red sharpie. I placed the case in the chamber and let the bolt fly with the bolt release. You can see the firing pin impression on the primer and the transfer of red pigment on the firing pin tip.

You are all welcome. My beer got warm, my pizza needs to be nuked again and I risked my firing pin bending or breaking. But at least now we all know.

And somebody clean this gun. It's dirty.

Post pizza edit to add: if you look at the OP picture, you will see that there is unburnt powder all over the carrier. The case failed at relatively low pressure, based on this observation. I'd bet that the gun wasn't failed and that if he put it together correctly the next time it works.

Fascinating, I would not have expected the pin to stay centered

 

[ToolAA]

While I haven't seen the rest of the gun or actually tried this trick live (in some other suckers gun of course) let me toss this into the MDS piranha tank:

Cam pin is in, this keeps the firing pin relatively centered. The firing pin retainer is clearly in or the pin would have fallen out the back of the carrier.

I just stripped a carrier and tried picking up a round (carrier only, no firing pin, it's MY gun!). The round ended up out of the mag, in the chamber, when I retracted the bolt carrier. If I let it go back in, let the bolt forward, and muzzle up the gun, loaded round ends up in the carrier center bore on retraction.

Since you guys have me thinking, View attachment 411980
Here's the bolt carrier as assembled by this idiot cam pin in the forward position.

View attachment 411981
Here's the carrier installed in the rifle the way the idiot did it.

View attachment 411983
Just for you guys, I took a piece of cleaned/annealed/sized/trimmed/chamfered/deburred PMC brass out of my stash. I took a spent primer, removed the anvil, drove the cup flat with a punch, pushed the anvil back in, and seated it in the case. I then colored the primer with a red sharpie. I placed the case in the chamber and let the bolt fly with the bolt release. You can see the firing pin impression on the primer and the transfer of red pigment on the firing pin tip.

You are all welcome. My beer got warm, my pizza needs to be nuked again and I risked my firing pin bending or breaking. But at least now we all know.

And somebody clean this gun. It's dirty.

Post pizza edit to add: if you look at the OP picture, you will see that there is unburnt powder all over the carrier. The case failed at relatively low pressure, based on this observation. I'd bet that the gun wasn't failed and that if he put it together correctly the next time it works.

We’ll good sir, you deserve a fresh beer and pizza for your scientific answer. Nice touch flattening out a used primer too. We’re all a little smarter today thanks to some idiot and his AR15 and some curious smart guy with some extra time on his hands.


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[4g64loser]

Wow, just wow.

Fascinating, I would not have expected the pin to stay centered

I could probably have rigged up a way to measure TIR on the firing pin but I wasn't thinking about it at the time. Based on observation, TIR was not going to be nearly enough to miss the primer at either extreme. Proven out by the test in practice. Lack of forward support will probably cause the firing pin to eventually fail if you did a lot of this.

 

[chilipeppermaniac]

What's TIR?

 

[4g64loser]

We’ll good sir, you deserve a fresh beer and pizza for your scientific answer. Nice touch flattening out a used primer too. We’re all a little smarter today thanks to some idiot and his AR15 and some curious smart guy with some extra time on his hands.


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I'll console myself with this here bourbon.

YOUR answers and write ups are scientific. On of these days I'll grow up and know how to make some of the toys you made.

I just took some crap apart and recreated someone else's stupidity (minus the live powder) I do admit I considered a live primer but figured the neighbors might call the cops and based on how stirred up the farmington fuckfest thread is, I don't want to have to sit in the dark after putting the M4 back together with a couple mags of 855a1 waiting for a knock on the door!

I've reverse (redneck)engineered more than a few firearms related oopses. Ranging from figuring out how someone fired multiple rounds of .40 through a glock 21 (he had a glock 22 there too, it turns out, and must have shot a cup and saucer grip), how 1919s were blowing top covers off with certain parts, how a guy wound up with a blaser tac2 bolt in his face (DO NOT shoot reloads in a blaser action unless you know how to accurately measure headspace datum and have confirmed that the case is being sized at least .005 under chamber dimension), etc.

 

[4g64loser]

What's TIR?

Total
Indicated
Runout

A measurement that describes total variance from a standard in dimensional terms. As it relates to the dipshit who put his bolt carrier group together about as completely as joe bidens thought process, it means how much wobble the firing pin exhibits in any direction, plus the amount it exhibits in a direction 180degrees opposite (thing up down or left right). If the runout measured at the firing pin tip were to exceed about .100 (perhaps a bit more), the primer going off would be luck. At either extreme, the firing pin might miss the anvil of the primer sufficiently to result in FTF. Small rifle primers are .175" in diameter. I don't recall the head size of the anvil but it's pretty small; probably around .050-070. start stacking up the runout extremes, subtract half the diameter of the firing pin tip, and you get the approximate amount of variance that will still PROBABLY set the primer off reliably.

Since even colt (this specific BCG is colt) does a garbage job fitting their firing pins to their bolt head bores (I know chads gonna hate me for that one!) compared to a top shelf bolt action rifle there is SOME runout even with the firing pin going though the carrier, the bolt tail, the cam pin, and the bolt face bore. There's a lot of moving crap, things get dirty, the gun still goes bang (blah blah blah). In short, you can't fit a machine gun that shits where it eats (direct gas impingement) to the tolerances of a precision boltgun and expect it to work. It just won't.

 

[jrumann59]

I don’t see how the BCG alone would chamber the round. Maybe without the bolt, the bottom edge of the BCG would hit the case head?

As for firing, that seems even more unlikely. Without the bolt to align the pin, perhaps the cam pin alone was just enough to keep it somewhat centered.

Still, with no bolt, the round could have not been fully chambered. With no bolt, the cartridge would have been pushing the pin back even before the hammer dropped. After looking closer at the mechanism I really dont see how it was chambered or fired.


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Good pics. The issue is as the round is being pushed into the chamber by the carrier the pin firing pin would interfere with round and would most likely keep the round from chambering in straight. The firing pin would be positioned over the round as the carrier strips the round out of the mag.

 

[jrumann59]

While I haven't seen the rest of the gun or actually tried this trick live (in some other suckers gun of course) let me toss this into the MDS piranha tank:

Cam pin is in, this keeps the firing pin relatively centered. The firing pin retainer is clearly in or the pin would have fallen out the back of the carrier.

I just stripped a carrier and tried picking up a round (carrier only, no firing pin, it's MY gun!). The round ended up out of the mag, in the chamber, when I retracted the bolt carrier. If I let it go back in, let the bolt forward, and muzzle up the gun, loaded round ends up in the carrier center bore on retraction.

Since you guys have me thinking, View attachment 411980
Here's the bolt carrier as assembled by this idiot cam pin in the forward position.

View attachment 411981
Here's the carrier installed in the rifle the way the idiot did it.

View attachment 411983
Just for you guys, I took a piece of cleaned/annealed/sized/trimmed/chamfered/deburred PMC brass out of my stash. I took a spent primer, removed the anvil, drove the cup flat with a punch, pushed the anvil back in, and seated it in the case. I then colored the primer with a red sharpie. I placed the case in the chamber and let the bolt fly with the bolt release. You can see the firing pin impression on the primer and the transfer of red pigment on the firing pin tip.

You are all welcome. My beer got warm, my pizza needs to be nuked again and I risked my firing pin bending or breaking. But at least now we all know.

And somebody clean this gun. It's dirty.

Post pizza edit to add: if you look at the OP picture, you will see that there is unburnt powder all over the carrier. The case failed at relatively low pressure, based on this observation. I'd bet that the gun wasn't failed and that if he put it together correctly the next time it works.

So the only way this could have happened is if the idiot had a chambered round removed his BCG and removed the bolt and put the Bolt Carrier back in on an already chambered round

 

[chilipeppermaniac]

Total
Indicated
Runout

A measurement that describes total variance from a standard in dimensional terms. As it relates to the dipshit who put his bolt carrier group together about as completely as joe bidens thought process, it means how much wobble the firing pin exhibits in any direction, plus the amount it exhibits in a direction 180degrees opposite (thing up down or left right). If the runout measured at the firing pin tip were to exceed about .100 (perhaps a bit more), the primer going off would be luck. At either extreme, the firing pin might miss the anvil of the primer sufficiently to result in FTF. Small rifle primers are .175" in diameter. I don't recall the head size of the anvil but it's pretty small; probably around .050-070. start stacking up the runout extremes, subtract half the diameter of the firing pin tip, and you get the approximate amount of variance that will still PROBABLY set the primer off reliably.

Since even colt (this specific BCG is colt) does a garbage job fitting their firing pins to their bolt head bores (I know chads gonna hate me for that one!) compared to a top shelf bolt action rifle there is SOME runout even with the firing pin going though the carrier, the bolt tail, the cam pin, and the bolt face bore. There's a lot of moving crap, things get dirty, the gun still goes bang (blah blah blah). In short, you can't fit a machine gun that shits where it eats (direct gas impingement) to the tolerances of a precision boltgun and expect it to work. It just won't.

Gotcha, 4g