6mm ARC

[A5BLASTER]

I think you still want to go with a longer gas system if possible. It's not 100% port size, even with an adjustable gas block, you can still have timing issues that make the gun more finicky to tune. I'm betting that Proof has this this cartridge pretty well figured out, so whatever barrel I buy is going to have the same length gas system, which from their page is rifle for the 16", rifle +1 for the 18", and I'd assume you'd want to go rifle +2 for over 20".

That's cool but I'm still going to test and see if normal gas lengths will work. If I do get one it will be a 12 inch.