Let me say first that you will need to have a special micrometer to measure shotgun bores accurately, a simple snap mike wont do.

In the case of the 16 gauge, if measured correctly it would be considered "modified"

In the case of the 12 gauge, if measured correctly it would be considered "full"

The nominal bore diameter for a 12 ga. is .730" ( give or take a few thousandth's for different manufacters)


Here's a simple break down of constrictions. These can be applied to any gauge, you just need the nominal bore diameter of the shotgun in question. Take the constriction and subtract it from the bore and the result is what your gun is choked at. Here's an example.....bore mikes out at .731 and the muzzle/choke tube measures .711", you wind up with "modified"


CONSTRICTION

Cylinder .000"

Skeet .005"

Imp Cylinder .010"

Lt Modified .015"

Modified .020"

Imp Modified .030"

Lt Full .035"

Full .040"

X-Full .045" +


The first measurements seem to be a bit odd, you stated .724", then .780" then .673"
This sounds as if the first measurement could have been .730" and the barrel is over-bored to .780" and then choked to .673. Over bored barrels are supposed to pattern better due to less shot deformation.

Hope this helps, doubleA