Custom 380 barrels have the larger 9mm 3/4" threads for installing an old-school 9mm SIONICS suppressor, or adapter, as well as having 1/2"-28 threads on the muzzle for installing a modern 9mm suppressor or AR15 type 9mm flash-hider/compensator.
Barrels, are physically/metallurgical identical to our M11/9 upgraded barrels, except chambered in 380.

Materials: 4140 Chrome-Moly steel.
Alignment: Bore-OD/Center.
Rifling: Button.
Twist: 1:10
Chamber: Upgraded (proprietary) from oem specifications & polished for improved feeding and extraction.
Suppressor contacts: 3/4-10tpi (oem/sionics) & 1/2-28tpi muzzle.
Suppressor alignments: 3/4" & 1/2" threads concentric with bore axis.
Length: 5 & 5/16" (OEM length)
Finish: Black oxide
Additional: Machined 7/8" wrench-flats for easy installation/removal

Thought they were cool and I would share them with the group

Its beautiful.......so how does this work?  Do I give you my address or something?

Thank you sir.  I am not trying to advertise, just wanted to get thoughts on this configuration

I'm new to the M11/9 world. Is converting from 9mm to .380 as simple as a barrel swap?

Short answer is yes, along with spring change, mag, and if you want to reduce the rate of fire some other minor mods.

This is not the main purpose of this barrel, although it would work.  The main purpose of this barrel is to allow someone to use their 9mm can on their 380 mac

So this would be a replacement barrel for the M11a1 to be able to thread a 9mm supressor?

correct

Well color me interested

you also need different ammo

Yup, although I thought about making barrels that said "whatever fits" for the caliber markings :)

fwiw, i have a dedicated upper with a .380 barrel for my M11/nine.
i'm using the same 9mm bolt assembly and mags. it runs great with a much
slower rate of fire and of course, suppresses well.