AR9 OOB detonation

So this happened a few days ago but I'm just now getting to writing this up. The pics you see below are the result of an out of battery detonation in my AR9. Before anyone says, oh I bet it was a double charge, no it was not. There are multiple pieces of brass with telltale signs (see pics) and I happened to be running this mag over a chrono when it happened. The gun is a hodge podge lower build with a 5 inch alpha shooting sports 9mm upper. Upper has an unknown number of rounds through it but at least 500, more likely 1000+. All of these have been reloads from the same press these incident rounds were loaded on. The previous loads have been 124gr bayou over 4.0gr of N320 and 147 HST over 3.8gr of N320. Never had an issue with these. The issue was with some blue bullets 147 round nose over 3.6gr of N320. I'm not blaming the bullet at all here, just saying these are what it happened with. This load shot great out of my pistols when I tested it. All of these rounds were loaded to the same COAL (don't have it handy, currently sitting in a tree stand). The issue is these rounds apparently did not fully chamber but were still able to be fired. Some of the spent cases have bulged ends as you can see in the pics but not all of them. Additionally some of these have pierced primers. Following the OOB detonation I cleaned the gun real well and tried it again with a shorter COAL. Same thing happened. All of these are loaded on a 650 with a lee factory crimp die in the last station. I then took the upper off, bolt out and plunk tested a few different rounds. Sure enough these sat almost 1/4 inch out of the chamber more than the rest (see pics, brass is the 147 blue bullet, nickel is a factory 147 gold dot). I couldn't even smash them in with my thumb. Very odd.

So I'm assuming the gun shouldn't have been able to fire while OOB? Something wrong with the upper or do I just continue to use the loads I know that work? Perhaps an out of spec firing pin? I had issues with the upper when I first got it (ejection and feeding) but got these resolved by bending the ejector and adding quarters to the back of the buffer tube. Both are fairly common AR9 issues and easily found fixes online. Anybody have an experience like this? I've searched online but couldn't come up with anything similar. Thanks and for you gurus out there trying to help me I can provide more info on gun, ammo, etc, just ask.

Colt AR9 bolts can not fire OOB. They are sharp edged on the bottom and the hammer will not reach the firing pin if the bolt isn't almost completely in battery. Other bolt manufs don't always do this. If you have a 'ramped bolt' to reduce trigger slap (and the hammer trying to beat the fire control group to death), they cut away the sharp edge on the bolt below the firing pin. That allows the hammer to be able to hit the pin while still not in battery.

Take a pic of the firing pin end of your bolt and post it.

Edit: this is a non-ramped bolt. You can see how the sharp edge (leftmost arrow) will block the hammer if the bolt isn't closed enough. Your situation is actually pretty common. Its dangerous to run a bump-fire or light/fast trigger on an AR9 upper and a ramped bolt. In your case you just have ammo that isn't in spec.

smdub said:

Colt AR9 bolts can not fire OOB. They are sharp edged on the bottom and the hammer will not reach the firing pin if the bolt isn't almost completely in battery. Other bolt manufs don't always do this. If you have a 'ramped bolt' to reduce trigger slap (and the hammer trying to beat the fire control group to death), they cut away the sharp edge on the bolt below the firing pin. That allows the hammer to be able to hit the pin while still not in battery.

Take a pic of the firing pin end of your bolt and post it.

Edit: this is a non-ramped bolt. You can see how the sharp edge (leftmost arrow) will block the hammer if the bolt isn't closed enough.

Click to expand...

This. Also, if you don't have a case gauge you probably should buy one. I gauge all my pistol and (bulk) rifle reloads. Dillon when I can, wilson when I can't. Cases that don't size properly are usually at fault. In a submachine gun, this problem can get very nasty very fast, nevermind a rifle caliber automatic.

https://www.mdshooters.com/showthread.php?175991&p=3847210#post3847210
https://www.mdshooters.com/showthread.php?t=242354&page=3 (post 50)

4g64loser said:

This. Also, if you don't have a case gauge you probably should buy one. I gauge all my pistol and (bulk) rifle reloads. Dillon when I can, wilson when I can't. Cases that don't size properly are usually at fault. In a submachine gun, this problem can get very nasty very fast, nevermind a rifle caliber automatic.

Click to expand...

Yeah I don't normally case gauge pistol ammo because it takes forever. Just thought about it sitting here but I need to measure those bullets when I get home. Potential they're out of spec and causing issue. Can't think of another reason these would be so far off from all the other 9mm I load. My press is essentially sizing the cases twice, once with the sizing die and once with the FCD. But I should've taken the calipers to the rounds after this happened I just kinda forgot about it.

smdub said:

Colt AR9 bolts can not fire OOB. They are sharp edged on the bottom and the hammer will not reach the firing pin if the bolt isn't almost completely in battery. Other bolt manufs don't always do this. If you have a 'ramped bolt' to reduce trigger slap (and the hammer trying to beat the fire control group to death), they cut away the sharp edge on the bolt below the firing pin. That allows the hammer to be able to hit the pin while still not in battery.

Take a pic of the firing pin end of your bolt and post it.

Edit: this is a non-ramped bolt. You can see how the sharp edge (leftmost arrow) will block the hammer if the bolt isn't closed enough. Your situation is actually pretty common. Its dangerous to run a bump-fire or light/fast trigger on an AR9 upper and a ramped bolt. In your case you just have ammo that isn't in spec.

Click to expand...

Thanks, I'll take a look at the bolt when I get home. I would like to replace this upper with a CMMG RDB bolt/barrel but they're unobtanium it seems.

kstone803 said:

I would like to replace this upper with a CMMG RDB bolt/barrel but they're unobtanium it seems.

Click to expand...

Back order from CMMG. I backordered a .22 AR BCG/Barrel. I had it in 3 weeks.

kstone803 said:

Thanks, I'll take a look at the bolt when I get home. I would like to replace this upper with a CMMG RDB bolt/barrel but they're unobtanium it seems.

Click to expand...

I just received mine after a long wait(under a year). They don't charge your card until they are shipping. In my case, my card was replaced by then and they emailed me with a couple options. I updated my payment method as per their instructions. It arrived a week later.

https://cmmg.com/barrel-and-bcg-kit-5-4140cm-sbn-9mm

teratos said:

Back order from CMMG. I backordered a .22 AR BCG/Barrel. I had it in 3 weeks.

Click to expand...

outrider58 said:

I just received mine after a long wait(under a year). They don't charge your card until they are shipping. In my case, my card was replaced by then and they emailed me with a couple options. I updated my payment method as per their instructions. It arrived a week later.

https://cmmg.com/barrel-and-bcg-kit-5-4140cm-sbn-9mm

Click to expand...

Thanks I think I'll do that. I'm on in stock notices at a few places but this is probably my best bet. Last notice I got was sold out before I could even add to cart.

kstone803 said:

Thanks I think I'll do that. I'm on in stock notices at a few places but this is probably my best bet. Last notice I got was sold out before I could even add to cart.

Click to expand...

Yes. Right now they are a "build for next customer in line" mode. I'm sure they are supplying other vendors but you never know how long their waiting lists are. I blew 7-8 months wait to hear from Optics Planet, then RTBA. I finally said screw it and went directly to the source. Get in line...

kstone803 said:

Thanks I think I'll do that. I'm on in stock notices at a few places but this is probably my best bet. Last notice I got was sold out before I could even add to cart.

Click to expand...

I kept doing that, and finally just back ordered from Brownells. I think that’s the only way to get one. Otherwise waiting for them to be in stock….you’re in line behind every single back order.

teratos said:

I kept doing that, and finally just back ordered from Brownells. I think that’s the only way to get one. Otherwise waiting for them to be in stock….you’re in line behind every single back order.

Click to expand...

Yep

smdub said:

Colt AR9 bolts can not fire OOB. They are sharp edged on the bottom and the hammer will not reach the firing pin if the bolt isn't almost completely in battery. Other bolt manufs don't always do this. If you have a 'ramped bolt' to reduce trigger slap (and the hammer trying to beat the fire control group to death), they cut away the sharp edge on the bolt below the firing pin. That allows the hammer to be able to hit the pin while still not in battery.

Take a pic of the firing pin end of your bolt and post it.

Edit: this is a non-ramped bolt. You can see how the sharp edge (leftmost arrow) will block the hammer if the bolt isn't closed enough. Your situation is actually pretty common. Its dangerous to run a bump-fire or light/fast trigger on an AR9 upper and a ramped bolt. In your case you just have ammo that isn't in spec.

Click to expand...

Appears to be a ramped bolt. For now I'm just going to shoot what I know works out of it and get on the wait list for the RDB combo.