Under the circumstances, I'd ask Numrich's your question about whether the barrels will fit your 16 frame. If they don't know, buy a set of 20s and a set of 12s and keep the receipts. I've always been able to send parts back to them OK as long as I did it by the book. That way you can see for yourself what fits and return what doesn't.
Somebody here may have actually fitted 420 barrels or have a method in mind. I don't know that action but if they are as easy as the hammerless single shots (220) you should have no problem.
Mike Armstrong aka Mesa
