Yes you can build a heavy barreled double, with barrels
as heavy as used on the NEF Ultra Slug gun.
The diameter needed for our slower powder 12ga loads, is
1.20" at the breech and 1.050" at muzzle. I have a
Zabala 10ga double that if I get time and money I want to
build a heavy barreled 12 ga bore gun. Like a 700NE only
our cases is longer and .029" more bore. But getting one
done is really expensive.And even 12ga doubles that are
premium, I haven't seen any with heavy enough muzzles.Ed