Case head separation with factory ammo

[stick]

Looks like an out of battery detonation.  Are you running a spacer in your buffer?  I'm also curious to hear more about the buffer tube issue you had.  Are you sure the Castle nut is tight and staked and is the buffer pin still functioning?

 

[ChuckS]

After cleaning my side charger PCC this evening, I thought of something. The detent that keeps the charge handle in place may be too strong and causing a delay or stoppage of the bolt as it returns to battery and screwing up the timing of the rifle. In fact, I think that is what you are demonstrating in your video. See if you can reduce the force required for that detent to where the buffer spring will push it closed unassisted.

 

Just a thought,

Chuck

 

[Neomet]

I'll pile on.  I think the case looks more like an out of battery detonation.  Not sure if you can slow the events down in your mind, but do you remember pulling the trigger before the detonation or is it possibly going off as the bolt slams home?  Do you have another 9mm bolt assembly lying around or that you can borrow?  

[Hi-Power Jack]

13 hours ago, ChuckS said:

Are you shooting minor ammo out of a 16.5" barrel?

 

No, 9mm Major out of a TruBor.

[Hi-Power Jack]

13 hours ago, ChuckS said:

Are you shooting minor ammo out of a 16.5" barrel?

 

No, 9mm Major out of a TruBor.

[Hi-Power Jack]

13 hours ago, ChuckS said:

Are you shooting minor ammo out of a 16.5" barrel?

 

No, 9mm Major out of a TruBor.

[Jeremyc_1999]

10 hours ago, ChuckS said:

After cleaning my side charger PCC this evening, I thought of something. The detent that keeps the charge handle in place may be too strong and causing a delay or stoppage of the bolt as it returns to battery and screwing up the timing of the rifle. In fact, I think that is what you are demonstrating in your video. See if you can reduce the force required for that detent to where the buffer spring will push it closed unassisted.

 

Just a thought,

Chuck

 

I'll see if I can adjust it.  If I let go of the bolt handle and it slams home, I have no issues.  I'm wondering if over time when it begins to get dirty if it is being held open

[Jeremyc_1999]

10 hours ago, Neomet said:

I'll pile on.  I think the case looks more like an out of battery detonation.  Not sure if you can slow the events down in your mind, but do you remember pulling the trigger before the detonation or is it possibly going off as the bolt slams home?  Do you have another 9mm bolt assembly lying around or that you can borrow?  

It has been happening when I pull the trigger.   If I knew it would solve the problem, I would buy a new bolt.  Unfortunately I don't have a spare bolt or know anyone with one.  

[Neomet]

Yeah, not sure that is where the problem is but thought if you had a spare it would help diagnose.  Sorry!

 

[Jeremyc_1999]

1 hour ago, Neomet said:

Yeah, not sure that is where the problem is but thought if you had a spare it would help diagnose.  Sorry!

 

No problem. really thinking about buying a taccom upper and then diagnosing the problem this winter

[HoMiE]

Most of the time I have witnessed “out of battery” detonation is was misdiagnosed as bullet setback. Especially if it happened on the first round or the first couple of shoots. The big stick mags loaded up tend to have the bullets pointed low and the round hits the barrel as it tries to load into chamber. Try and measure the OAL on the bullet then chamber. Then pull bullet back out and measure and see if it is pushing bullet back or if OAL has changed. 

[Patrick Scott]

There is nothing in standard AR15 style 9mm rifles to stop the hammer from falling if the bolt is out of battery slightly. 
If in fact you are getting out of battery blow outs, I would focus on why the bolt is out of battery.  Could be rounds loaded too long or otherwise out of spec not allowing the bolt to close fully. Could be some sort of cartridge damage while feeding. Could be chamber issues.  I have seen bolt bounce do this before, but if its doing on a manually fed round, its not bolt bounce. 

[Jeremyc_1999]

3 minutes ago, Patrick Scott said:

There is nothing in standard AR15 style 9mm rifles to stop the hammer from falling if the bolt is out of battery slightly. 
If in fact you are getting out of battery blow outs, I would focus on why the bolt is out of battery.  Could be rounds loaded too long or otherwise out of spec not allowing the bolt to close fully. Could be some sort of cartridge damage while feeding. Could be chamber issues.  I have seen bolt bounce do this before, but if its doing on a manually fed round, its not bolt bounce. 

Thank you for the informative reply.  It did it once on a manually fed round and the other 3 times have been after the first shot.  It has done it with at least 3 and maybe 4 different magazines - 1 glock 15 mag, 1 glock 17 mag, 1 glock 33 round mag, 1 glock 33 round mag with mbx 47 round extension (I am pretty sure.  This may have been the 33 round mag.  it was the first one and i didn't pay particular attention to the magazine) 

[longbeard]

Your video makes me wonder if your trigger isn't hanging up on bolt a bit?

OOB is a flaw of the platform. It readily happens to most when stepped brass splits in the chamber.

Sent from my SM-N950U using Tapatalk

[Jeremyc_1999]

So, I changed the buffer and spring and went out and shot again tonight.  I had on blown case and 2 other bulged cases.  I didn't know about the bulged cases until I was picking up brass.  I also lightened the detent spring on the charging handle when I got home, but I doubt this will help because the changing handle is only used on the first round and I have only had one of the seven failures on the first round.  Any other Ideas?  I have a ramp ordered from Taccomm that I am going to put in the upper and see if that will fix the problem, but am open to any other ideas. 

[Jeremyc_1999]

Also, as you can see much of my brass is very very dirty

[Patrick Scott]

Load up some dummy rounds and find out why the gun isnt going fully into battery. I kinda doubt its buffer/buffer spring related. 

[Jeremyc_1999]

1 minute ago, Patrick Scott said:

Load up some dummy rounds and find out why the gun isnt going fully into battery. I kinda doubt its buffer/buffer spring related. 

The tough part is it is going into battery when I cycle the charging handle.  It seems to happen middle of a magazine so it is hard to replicate

[Patrick Scott]

5 minutes ago, Jeremyc_1999 said:

The tough part is it is going into battery when I cycle the charging handle.  It seems to happen middle of a magazine so it is hard to replicate

But it has done it when cycling the charging handle, correct? It might take some tries to duplicate it and figure it out.
When using loaded round shoot slowly and inspect whats going on with the gun after every shot. 

[Neomet]

14 minutes ago, Jeremyc_1999 said:

Also, as you can see much of my brass is very very dirty

 

It completely looks like your cases are not sealing into the chamber.  There are a number of potential reasons for this including ultra light loads but since you are using factory ammo I doubt that is it.  

 

[HoMiE]

Does it happen when firing slow?

 

is the bolt bouncing? What is the eight of bolt and buffer?

[Jeremyc_1999]

13 minutes ago, HoMiE said:

Does it happen when firing slow?

 

is the bolt bouncing? What is the eight of bolt and buffer?

I have had it happen slow firing and rapid firing both

Bolt weight 16.9 oz 

buffer weight 3.8 oz

[HoMiE]

5 minutes ago, Jeremyc_1999 said:

I have had it happen slow firing and rapid firing both

Bolt weight 16.9 oz 

buffer weight 3.8 oz

I suspect your buffer is way too light 

 

 

[TRUBL]

the bolt and buffer weight seems to be just fine.......20 to 22 ounces seems to be about perfect for loads in the 125 to 150ish PF as a rule of thumb. Looking at your dirty cases and the bulged ones......one would think that it out of battery, that could not be more wrong. You mmmmmmight want to chronograph your loads once.....they mmmmmmight be too hot for the spring you are using. We talked on the phone earlier......at the time I suspected you might be pushing rounds back into the brass. So checking the crimp would still be something to check. I am saying all this stuff....but am not there so these are more shots in the dark than any thing. If your crimp is good now, you might not have enough spring and the bolt may be going back too soon......that is typically shown by dirty and blow out cases like you have. 

 

Now.....here is the quandary......IF......you are pushing bullets back into the case, even a 308 spring is not going to help slowing the bolt down as much as you need. The case is coming out AFTER you ignite it. It is pretty much physically impossible for the case to be that far out of battery and have the hammer hit the firing pin. so if the issue is pushed in bullets.....the ramp should take care of that. IF it is a spring issue, try heavier, once you get the ramp installed. I'm gonna go out on ledge here and say you are still pushing bullets in the case to get the pressure signs you are saying......with a secondary issue of possibly not enough spring for the loading you are presently doing. Regardless......chrony the present loads to see how that is looking. Another secondary issue is your chamber mmmmmmmmmaybe too loose. Again......only speculation as I am not there.

 

Tim

[longbeard]

You've checked the following?

• There is nothing in the chamber.  Look real close.  I was fooled before on this.  A little ring of brass can sit real flush in there making it hard to see.
• The extractor isn't hanging up the bolt.  I've had a combo where they rubbed so hard it gouged the bolt.
• The hammer isn't hanging up the bolt.
• The buffer and tube they replaced are for carbines.

If all are in check. I agree with Homie.  Most run a 14-15 oz. bolt with a 6 oz. "ish" buffer.  While your total weight is the same it would merit looking at it.