12 ga choke screw in choke tooling is easy to find.. Harder for 10. 10 ga screw in chokes, are available though.. Single pointing and getting everything right on a lathe, would not be fun.
A Jug choke is easiest. A section of bore before muzzle, is opened up with an expanding reamer.
A simple muzzle swage is UGLY, and less efficient. Muzzle is simply crimped to smaller OD/ID.
A Polychoke style silver braze on model, would work... And be adjustable. And also a 10 Ga problem child...
Shotgun tooling is kind of $$$. Sometimes its just best, to send out to someone who has it...
You only get one shot, Then you get to buy a new barrel if something goes wrong (assuming you have barrel at ~18 in)........ A Polychoke permanently attached choke, can save you one time though.