Headspace on 9mm AR

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cyclesarge
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Headspace on 9mm AR

Post by cyclesarge »

Is this an issue. I am planning the next stage of my 9mm Ar build (the upper) and came upon the headspacing debate over .223 but couldn't find anything on the 9mm.
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Twinsen
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Post by Twinsen »

Ignore my post.
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Walker Precision
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Re: Headspace on 9mm AR

Post by Walker Precision »

cyclesarge wrote:Is this an issue. I am planning the next stage of my 9mm Ar build (the upper) and came upon the headspacing debate over .223 but couldn't find anything on the 9mm.
It should be checked when putting the upper together. You can do it pretty easy with a loaded round and a set of dial calipers. The depth of the bolt face should be .125" +/- a few thousandths. A loaded round should stick out of the chamber about the same amount.
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cyclesarge
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Post by cyclesarge »

So if I put a shell in the chamber, the bolt should be touching the face of the chamber? So What I am actually checking is the amount of the shell that sticks out of the chamber which should be the same amount of the shell that sticks into the bolt?
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Post by Walker Precision »

cyclesarge wrote:So if I put a shell in the chamber, the bolt should be touching the face of the chamber? So What I am actually checking is the amount of the shell that sticks out of the chamber which should be the same amount of the shell that sticks into the bolt?
Yep. If the bolt does not touch the barrel, head space it too short. If there is a large gap between the case head and the bolt face, you will get light primer strikes.
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HAL
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Re: Headspace on 9mm AR

Post by HAL »

1 - BE AWARE -- common comercial 9mm case length runs from .744 to .749 with .746 being an average case length. I had 1 barrel made. and bought a second later on. The first barrel had the case sunk too deep into the barrel (chamber), leaving approx .035 gap from bolt face to the case head,, fire pin would not hit primer.. I had to face the barrel off and the flange to set barrel back in reciever to bring the works together..

I bought a short barrel couple yr ago from Garrison Mfg.. chamber was deep on it too, but not as bad, but still not to my satisfaction.. I had barrel faced to bring case head to stick out .130/.135 depending on which brand case was being used for lot of handloaded ammo (I load all my own).

With 0.135 case head out of barrel, and the 0.125 pocket of bolt face, I maintain approx 0.010 gap from bolt face and barrel face with loaded round in the chamber.. only time bolt slaps barrel is on empty chamber (I run VM Hy-Tech block and Uzi mags).. Here is what my chambered round and bolt meet the case head and case mouth sandwich..



Image

Image

This is the original I had made in 2003, you can see where I had to set the barrel back to correct the headspace (note cut between pin and flange) and face the barrel face to get my desired case protrusion. -
Image
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bikefreek
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Re: Headspace on 9mm AR

Post by bikefreek »

looks like your barrel extension is cracked right by your indexing pin....
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Re: Headspace on 9mm AR

Post by borgem »

I know this is resurrecting an old thread, but for those who find this thread like I did just now, there was a great discussion on this thread http://www.northeastshooters.com/vbulle ... ce-KABOOM/ that covers both headspace and unsupported case length in the ramped area of the 9mm barrel/throat (if your barrel is ramped, that is)...

According to the folks over there, the "rule of thumb" is that you want ≤ 0.100" of the case unsupported or you risk bulging...or worse.
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Re: Headspace on 9mm AR

Post by fishman »

borgem wrote:I know this is resurrecting an old thread, but for those who find this thread like I did just now, there was a great discussion on this thread http://www.northeastshooters.com/vbulle ... ce-KABOOM/ that covers both headspace and unsupported case length in the ramped area of the 9mm barrel/throat (if your barrel is ramped, that is)...

According to the folks over there, the "rule of thumb" is that you want ≤ 0.100" of the case unsupported or you risk bulging...or worse.
Wow, thats really good to know. be safe everyone.
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Re: Headspace on 9mm AR

Post by TOOL1075 »

HAL wrote:1 - BE AWARE -- common comercial 9mm case length runs from .744 to .749 with .746 being an average case length. I had 1 barrel made. and bought a second later on. The first barrel had the case sunk too deep into the barrel (chamber), leaving approx .035 gap from bolt face to the case head,, fire pin would not hit primer.. I had to face the barrel off and the flange to set barrel back in reciever to bring the works together..

I bought a short barrel couple yr ago from Garrison Mfg.. chamber was deep on it too, but not as bad, but still not to my satisfaction.. I had barrel faced to bring case head to stick out .130/.135 depending on which brand case was being used for lot of handloaded ammo (I load all my own).

With 0.135 case head out of barrel, and the 0.125 pocket of bolt face, I maintain approx 0.010 gap from bolt face and barrel face with loaded round in the chamber.. only time bolt slaps barrel is on empty chamber (I run VM Hy-Tech block and Uzi mags).. Here is what my chambered round and bolt meet the case head and case mouth sandwich..



Image

Image

This is the original I had made in 2003, you can see where I had to set the barrel back to correct the headspace (note cut between pin and flange) and face the barrel face to get my desired case protrusion. -
Image
Bumping this for good info.
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