Hello everyone,
I have a few questions for an AR9 build that I am planning. Does anyone know the outer diameter of Ballistic Advantage's 16" 9mm straight profile barrel? I'm looking to build up my AR9 as a 16" rifle and would like to use a delta ring assembly, end cap, and install a FSB. I know that since AR9s are simple gas blowback that there is no need for a gas black journal. However, if the straight profile is 0.750" I can still install a gas block or a FSB to hold the end cap captive (and use front iron sights) and therefore use a 2 piece handguard.

Is there any reason to select a 1/2-28 or a 1/2-36 muzzle thread?

A2 tube, buffer, spring: ok for AR9 setup or do I really need something fancier/more dedicated? I wanted to set up an A2 stock on the rifle.

To give an overall idea of the vision, I was going to try for something like the BRN Proto but in 9mm.

Thank you for your help.

I would like to know as well.  Would make for a cool "dissy" build.  I wanted to do this with a CMMG barrel but it is undersized and even tapered.  That BA barrel could be the cat's meow.  I have their 8.3" 9mm barrel on a "pistol" and it is a shooter.

i have two colt barrels that are 1/2 x 36 and cant find a asr mount for my hybrid 46 to use on them

1/2 x 36 is colts red headed step child of threads given a choice i would go with 1/2 x 28

Thank you. I'll go with 1/2-28. I will contact BA to see if they can tell me the outer diameter of their 16", 9mm straight profile barrel.

Hi,
I got a reply from BA:

"Thank you for reaching out to us.  I hope this message finds you well.  The OD is .725" and will not fit an FSB.  Currently, we are not offering a 16" barrel in 9mm that fits an FSB."

So looks like it's not an option yet.

My AR9 carbine had a NFA 16" barrel that was .750" diameter. 1/2x36 threads.

Dang.  Another case of the barrel maker not on the same page as the gun crafters.

Try JSE surplus.

 Too easy.

Find a FSB that is .625 ID for pencil barrel.

Call ADCO, or Macon Armory,  other similar shop.

Send them parts and a check or CC number.

They will ream ID of FSB to OD of the barrel. And then stake it correctly.

Then you'll have want you want.




.

Will a non f marked be ok on a 9mm? My son wants to build an A2 style 9mm. We have a lower on the way. Reaming a fsb shouldn’t be too hard on a mill. Now I need to find a cheap one to practice on

This KAK barrel is what you want, alas it's out of stock.

If you use a 1/2 X 28 thread instead of the 1/2 x 36 for the 9mm be sure to check the bore on the muzzle device to make sure it"s the correct size.

Check out the 8th post down on the "Why are most 9mm specific buffers solid?" thread in this same PCC section.  I'm not going to repost it all here but I explained there how I repack and modify A2 rifle buffers to work with PCC blowback guns.  Works excellently for me.

YMMV

Sooo close.  If only the GB journal was at rifle length......