I need 9mm AR chamber dimensions.

[Richard/SIA]

I have some 9mm barrel blanks I want to use up.
Should probably do them ASAP in case they need to be "Grandfathered" before sedition wins in congress.

Thinking I should make them into 9mm AR barrels, probably suppressed.

All I need are three simple measurements.

How far the case protrudes from the chamber.
Than angle of the feed ramp into the chamber.
The outside diameter of the feed ramp in the chamber.

Surely some one here can make or otherwise provide those few measurements?

[eastern_hunter]

Have cut 9mm barrel stock into AR barrels in the past. Using a COLT bolt, I cut the chamber such that the end of the case is exposed by 0.130". Means the bolt will just barely clear the barrel putting full force on the end of the case. As you cut the chamber, test fit a case and watch the coverage of the case move back ... should be well into the internal web of the brass!

A COLT barrel does not have a ramp per se ... ramp is built into the front magazine block. The edge of the chamber is broken and polished round so that projectiles do not get caught on the edge of the chamber.

Sorry the uppers are together otherwise I'd take pics for you.

Is probably a good idea to cut the ridge at the end of what would be a barrel extension a bit thick ... as that allows facing the chamber end and moving the back edge of that ridge forward if you need to reduce the depth of the chamber.

[Richard/SIA]

Cannot be assured they will always be used on a Colt set-up.

There are several kits on the market, all back-ordered right now.
Brownells even caries them.
I was thinking of something like this, which should work with all of them.



I just need to get a mag for testing.

[redtazdog]

You don't realy need a 12:00 index pin.

[eastern_hunter]

No you don't need the pin, but it does remove one degree of movement freedom which is never a bad thing for accuracy.

[redtazdog]

No you don't need the pin, but it does remove one degree of movement freedom which is never a bad thing for accuracy.

Without a gas block front sight the pin does nothing for accuracy if your barrel nut is tight like it should be.

[Richard/SIA]

I always understood that it primarily kept a consistent point of impact/aim.

[redtazdog]

I have several short barrel 9mm builds and made several 9mm barrels and none of them have a 12:00 index pin and they have never changed POI or have had any accuracy change.
Some of the barrels I have purchased in the past didnt have a pin and was not even drilled for one.
How would a small pistol caliber barrel move or twist at all when the pressure from a nut is holding it in place.
The pin is more for the gas guns to get the bolt lugs fsb and gas port at 12:00
You can install a pin on a super short 9mm barrel if you feel the need as it only takes another few minutes but
if you dont have a front sight on it that needs to be at 12:00 then why.

r

[Richard/SIA]

Even most STEN's had an index pin.

Any real difference would probably only be apparent at longer ranges.

[TOOL1075]

Have cut 9mm barrel stock into AR barrels in the past. Using a COLT bolt, I cut the chamber such that the end of the case is exposed by 0.130". Means the bolt will just barely clear the barrel putting full force on the end of the case. As you cut the chamber, test fit a case and watch the coverage of the case move back ... should be well into the internal web of the brass!

A COLT barrel does not have a ramp per se ... ramp is built into the front magazine block. The edge of the chamber is broken and polished round so that projectiles do not get caught on the edge of the chamber.

Sorry the uppers are together otherwise I'd take pics for you.

Is probably a good idea to cut the ridge at the end of what would be a barrel extension a bit thick ... as that allows facing the chamber end and moving the back edge of that ridge forward if you need to reduce the depth of the chamber.

Bumping and quoting for good information.

This is part of a string of posts pertinent to the issue of quieting the 9mm AR platform (reducing bolt closing noise by offsetting bolt impact from chamber face).

[Mageever]

Cool info. I love the idea of making a 9mm AR that is quieter for the shooter. I recently metered one that was almost 10 dB louder at the shooters ear than an MP5.

Thanks for dredging this up Tool. And welcome back!