So pretty much zero options for a factory built aftermarket barrel unless you have an op rod custom made.
On the + side to that a custom barrel cut from a match blank while costing you $500 will allow you to address the gassing and tune the rifle perfectly if you have access to a quality drill set with very small increments between bits. This is how I tuned my NR ACR 300BLK barrel, I had my barrel maker/machinist drill a tiny hole then tested and used my drill press to open it up a little at a time till it cycled my supersonic and subsonic loads perfectly.
I'm in the process of making up a prototype barrel with exactly that - 18.6" / carbine gas system... I'll post more once I've been able to test it on the WK 180. A .300 Blackout conversion would be excellent as well!


















































