There are tons of people who shoot "sub-gauge tubes", people who own one $15,000 O/U, shoot skeet in all 4 classes (12ga, 20ga, 28ga, .410 bore), and they use the exact same 12-ga shotgun to do this, so that thge gun handles exactly the same.
Other folks do the same thing with the same shotgun with 3 additional sets of barrels in each gauge, for an additional 10-grand or so............
The folks using 20-gauge have trouble with the tubes cracking if you get close to the full pressures of the 20-gauge, because the insert tubeset is VERY thin.
No such trouble with 28 and .410 because the tubes are plenty thick.
I don't always venture out into the sub-freezing darkness, but when I do, it is hunting season, and I carry a Browning. Stay hungry my friends.