This is why you check headspace: KABOOM

[warwickben]

You should take a look at how Olympic arms cuts there chambers . They use a special bolt that is coned shape so thae can have a longer feed ramp not exposing the case . When I was clambering my 45 I was told to use less then .100 exposed .

 

[bigblue]

You should take a look at how Olympic arms cuts there chambers . They use a special bolt that is coned shape so thae can have a longer feed ramp not exposing the case . When I was clambering my 45 I was told to use less then .100 exposed .

Everything I have read says .125-.135 of the rim should be exposed past the end of the barrel. If you ream the feed ramps aggressively you are guaranteed to expose a ton of the case wall.

 

[warwickben]

That's how my friend makes them

 

[mac1911]

Ok so this thread grabs my interest as I have some more parts that magically appeared and was thinking of 9mm.
I'm really curious though of few things.
Is this a head space issue? Head space on a straight cased pistol rounds is from case mouth to face of the bolt correct?
Trying to word this correctly.
Is the headspace problem or just the feed ramp cut to deeply?
I'm also wondering , other than the easy of manufacturing. Why is the feed ramp cut around the entire circumference of the barrel?

I look at the pictures and see that using a headspace gauge and get a go on the check would not help with the deep feed ramp issue.

 

[beaker]

Ok so this thread grabs my interest as I have some more parts that magically appeared and was thinking of 9mm.
I'm really curious though of few things.
Is this a head space issue? Head space on a straight cased pistol rounds is from case mouth to face of the bolt correct?
Trying to word this correctly.
Is the headspace problem or just the feed ramp cut to deeply?
I'm also wondering , other than the easy of manufacturing. Why is the feed ramp cut around the entire circumference of the barrel?

I look at the pictures and see that using a headspace gauge and get a go on the check would not help with the deep feed ramp issue.

I'll check my Uzi, I think it is buried pretty far into the chamber. These are sticking out a mile...

 

[bigblue]

I had a local gun smith take a look at it and the go/no-go gauges definitely did not help diagnose the problem. This is because the total seating distance is the same amongst the barrels we looked at. The difference is how deep the feed ramps are cut and as you can see, there are wide variations in how that is done.

 

[mac1911]

So basically until knowing folks could check headspace and all could check out fine.
I'm completely new to 9mm ARs I imagine the feed ramp groove helps with reliable function.
What I don't know if there is a spec for the feed ramp.

Also is there a set standard to the web thickness of 9mm. Could this be a ammunition malfunction?

 

[R6YamaJim]

This is how my cmmg barrel chambers. Build two of these so far.

 

[bigblue]

So basically until knowing folks could check headspace and all could check out fine.
I'm completely new to 9mm ARs I imagine the feed ramp groove helps with reliable function.
What I don't know if there is a spec for the feed ramp.

Also is there a set standard to the web thickness of 9mm. Could this be a ammunition malfunction?

As I wrote in the OP, I think ammo played a part but if the case wall wasn't exposed that much I don't think there would have been a rupture.

 

[bigblue]

This is how my cmmg barrel chambers. Build two of these so far.

Hmmm that feed ramp makes me question buying a CMMG barrel as that looks deep.

No easy answers.

 

[Kevin_NH]

Anybody running the 10.5" Palmetto State Armory AR-9? How's it look?

 

[R6YamaJim]

Round chambered bolt closed. Don't know if this helps.

 

[bigblue]

Round chambered bolt closed. Don't know if this helps.

Who makes that barrel & bolt?

 

[R6YamaJim]

Both are CMMG.

 

[beaker]

Here is an Uzi barrel/chamber. It is chambered right up to the transition to the rim.

 

[massBRS]

interesting read - I have a 9mm AR in the works for the mrs.

 

[warwickben]

Ok so this thread grabs my interest as I have some more parts that magically appeared and was thinking of 9mm.
I'm really curious though of few things.
Is this a head space issue? Head space on a straight cased pistol rounds is from case mouth to face of the bolt correct?
Trying to word this correctly.
Is the headspace problem or just the feed ramp cut to deeply?
I'm also wondering , other than the easy of manufacturing. Why is the feed ramp cut around the entire circumference of the barrel?

I look at the pictures and see that using a headspace gauge and get a go on the check would not help with the deep feed ramp issue.

Besides of east of manufacturing having the feed ramp all the way around (simple op on a lathe).
Having it all the way around directs it to the center better.
Feeding from a single stack mag you could get away with it being mainly on the bottom and little on the sides. Think a 1911 barrel. Having the feed ramp on top will force rounds that started to feed high back down to the center . A 1911 barrel hood section dose the same thing .
On the ar45 I made and my ak 45 I made I found some times the rounds would pop up high some times and adding a chamfer on the top help keep the bullet from just jamming .

For the ar it's more of a problem with the bolt face . You need the mag mounted high, since the section of the bolt that strips the round doesn't stick down that far .most pistol cal mags the top round angles up. A stang (m16/m4/ar15 mag ect) the rounds sit flat at the top and the feed Ramps push them up and into the chamber .
On my ak45 since the akm bolt face stripper sections(I don't know what to call it) hangs lower I was able to mount the mags lower then my ar45 build. This makes it less likely to hit the top of the chamber but some time the way the round pops out it hit so I added the chamfer in top.
From the few scratch builds I have done feeding is a freaking black art.

Rule of thumb on pistol rounds you should have , .100 or less unsupported case. I basically copied a few barrels I had around. It comes down to the caliber and what the case can handle . Higher pressure rounds you need to have it chambered deeper then a lower pressure round.

 

[bigblue]

I wanted to update everyone on how the vendors involved responded to this. I'm going to write a whole thread on the CS responses so this is just a synopsis. Bear in mind that in both my and the gun smith's opinion the barrel is the primary culprit here:

ADCO (Barrel mfg): Refunded barrel, claimed it is in spec and refused to pay damages.
Tula (ammo mfg): Did not question, argue, or even ask to see the ammo and paid all damages in addition to refunding ammo.
UTG (handguard mfg): Replacing barrel nut & screws; requests damaged items for research & QC inspection.

 

[warwickben]

I wanted to update everyone on how the vendors involved responded to this. I'm going to write a whole thread on the CS responses so this is just a synopsis. Bear in mind that in both my and the gun smith's opinion the barrel is the primary culprit here:

ADCO (Barrel mfg): Refunded barrel, claimed it is in spec and refused to pay damages.
Tula (ammo mfg): Did not question, argue, or even ask to see the ammo and paid all damages in addition to refunding ammo.
UTG (handguard mfg): Replacing barrel nut & screws; requests damaged items for research & QC inspection.

I thought it was Airsoft only .... Guess I was wrong .

 

[bigblue]

UTG has a new "Pro" line that is made in the USA and is actually good quality stuff.

"UTG Pro - not just for Airsoft anymore." lol

 

[bigblue]

I thought that I had included pics of the Tula ammo that was slightly larger than the case gauge in the OP but reading back I did not.

So making the barrel problem worse is that Brassmaxx is a little dirtier than normal (which really shouldn't cause a problem if the chamber is safe) and the fact that several rounds did not slide easily into the case gauge (which again, shouldn't cause a huge problem with a safe chamber).

I do not think the rounds are out of spec enough to cause a problem on their own. Combined with the deep feed ramps an unsafe condition is clearly created.

In other words, each condition taken on its own is not enough to cause a failure but combined they did.

 

[drgrant]

I've probably reloaded like, 8000 rounds of 9mm in my time, and I don't think I've ever had one that was that bad WRT the gauge. Is it possible the gun fired out of battery?

-Mike

 

[thormx538]

Is it possible the gun fired out of battery?

Well yeah, I think that's what's happening here. The simple blowback design of the 9mm AR's allows for that. The issue is why was the round not going in to battery -- too dirty, out of spec round, out of spec chamber?

 

[bigblue]

The issue is why was the round not going in to battery -- too dirty, out of spec round, out of spec chamber?

I think it was all of the above, which is what I have tried to present and argue.

 

[bigblue]

.

 

[BostonBullit]

That's a factory round in the gauge? Holy Crap. I gauge every round off my press and when one looks like that it goes in the "pull" bucket. That thing might not even chamber in a glock :-D

 

[bigblue]

Bullit, that is factory Tula in a Dillon case gauge.

The new CMMG barrel came Monday and I like it. The chambering is much better than the ADCO barrel:
View attachment 135257

The new barrel is 8.5" vs the 5" previous barrel, which allows me to use a different comp:
View attachment 135258

I did get to the range yesterday after work to function test and break it in. I put 3-400 rounds through the rifle and have to trim some of my magazine cuts but the barrel was flawless.

 

[JeepinMaxx]

sorry to dig up an old post - but I just saw it and it concerned me. I have a YHM barrel so I dropped a factory round in. It looks ok to me

I've had the set-up for a few years with no problem. I clean my gun after every match, so that may skew my results

 

[whacko]

Pardon my ignorance, but what's the point of a 9mm AR15? Why not leave the rifle .223/5.56 (as originally designed), and save 9mm ammo for a pistol (as originally designed)?
Not trying to pull anyone's leg, just really wondering why bother adapting a rifle to a pistol caliber.

Cowboys liked having their pistol and rifle use the same ammo. The benefits are there even giving up some range out of the rifle.....

 

[bigblue]

sorry to dig up an old post - but I just saw it and it concerned me. I have a YHM barrel so I dropped a factory round in. It looks ok to me

I've had the set-up for a few years with no problem. I clean my gun after every match, so that may skew my results

If your chamber is always clean and you never run into ammo that is slightly out of spec you will be fine. Luck does play its part.


To the question about why adapt a pistol caliber to a carbine in the first place: At Hopkinton we have 25y pistol bay/action pits where we setup steel, paper, and VTAC boards. The PCC allows us to practice the same manual of arms at a shorter distance with standard ammo and keep the cost down.

9mm drops ~6" at 100y & a few feet at 200y. We generally get less than dinner plate accuracy on the 200y steel and it has plenty of energy to move flippers on a dueling tree at that distance. Really, you aren't losing much at the distances most ranges have around here. At 400y? Yeah that's like dropping a mortar round in but ask Jerry: It's very possible.