Is this high enough presure?

[Dakotared]

I got a 9mm ar15 upper. The round is safe in my hand gun. When I picked up my cases I found this. I know I should have reworked up the load for the new gun I was an idiot No harm this time but I got lucky. This is a reminder to all ways work up a load for any new gun you get.

[Erud]

Were these not fully in battery when fired?


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[andrewP]

Were these not fully in battery when fired?


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That's a plausible explanation for why they'd look like that. If that's the case, though, what would cause the gun to fire out of battery?

[usnret]

I have a 9mm AR, and I shoot the same rounds that I shoot in my handguns in it. There is something else going on here like firing out of battery.

You need to take the upper off and see if a round will just drop into the chamber.

In fact you should maybe get some factory rounds and try them to see if you get the same results.

[Dakotared]

these did come out after rapid fire. Slow fire there is a slight noticeable ring that you can see but not feel. My thoughts were it was starting to eject the case before the bullet left the barrel. Maybe a heavier buffer or stiffer spring?

[steve4102]

What are the details of your load?

Did you check the OAL to make sure this load would fully chamber. Those look more like Out of Battery then High pressure to me.

[Bitter Bastard]

Do you have the right 9mm heavy buffer in your AR? It could be caused by starting to unlock too soon. Is unlock even the right word for a blowback gun? Having a brain cramp on that one right now.

First, check to make sure you have the right buffer and spring. Check for other broken parts, then try some factory ammo and see what you get. I've never seen brass like that out of my Colt 9mm SBR even when bump firing it.

[MWAG]

Do you have the right 9mm heavy buffer in your AR? It could be caused by starting to unlock too soon. Is unlock even the right word for a blowback gun? Having a brain cramp on that one right now.

First, check to make sure you have the right buffer and spring. Check for other broken parts, then try some factory ammo and see what you get. I've never seen brass like that out of my Colt 9mm SBR even when bump firing it.

Correct. The dwell timing is off. The barrel is still pressurized when the bolt assembly unlocks to cycle in the next round, pushing the round back and out too soon. This is what's causing the case expansion.

[Dakotared]

I am using a standard 223 buffer. I was not aware that I needed a different one until I saw this problem and started to look into it. What weight do you guys recommend? I have found them as heavy as 9 oz for a 9mm upper.

[Bitter Bastard]

I am using a standard 223 buffer. I was not aware that I needed a different one until I saw this problem and started to look into it. What weight do you guys recommend? I have found them as heavy as 9 oz for a 9mm upper.

I just run the standard Colt 9mm buffer, I think it is 5.5 ounces. I've heard good things about the heavier ones but never tried one personally. I tend to run pretty stock setups unless there is a compelling reason not to.


Bitter Bastard

[mahnster]

I run a RRA 9mm buffer that's around 5.6 ounces. Start with a standard 9mm buffer and work from there.