Contact John at Retro Arms Works. I’m not sure if he’ll do a chop and thread but it wouldn’t surprise me if he did and he was super fast to deal with. I have a thread about using his shop from the last two or three months I think.
I’m not sure what his turnaround time is but it is absolutely worth the call. If you want The Best. The Jedi Master of Barrelogy…
He’s done cut downs for a buddy of mine, several in fact, and some ball milling for me that was just beautiful craftsmanship. Marvin can cut down and rethread, re-profile, flute, ball mill, cerakote and quite a bit more. I’ve got a price sheet if you want I can email it to you. I think his prices are fair, but his work is worth it regardless.