I have a 1941 vintage Model 42 marked "Full" which mikes .015". I don't believe it has been modified. Some time ago I tested a Verney Carron SxS .410 miking .010" and .030". The shot actually did squeeze out of that .030" barrel, but I never patterned it. A friend made two honest 40 yard quail shots with it, so it must work.
Briley lists their idea of standard choke constrictions for each gauge. In .410 .010" is listed at Light Modified and .020" is called Xtra Full.
I have another 42 which has Briley screw chokes installed and one of them is .019". It puts out an effective Full pattern with 2-1/2" shells.
