My brother has a Joseph Lang, but it is a single shot, built in 1853.. in 99% condition.

16 bore

That day at the range, we tested only one load, .022" patch and a .648" round ball. The patches were just a little thin, but the 85gr. 2F GOEX charge did not burn them.
The muzzle is a little sharp cornered and mildly cut the patches on most every land, but sealed well enough to only scorch the patches in the groove locations.
At 50 yards, we both cut a single hole for 5 shots.
At 100 meters, the 5-shot group Taylor printed, was approximately, iirc, 1.650" x 1.624".

I shot my 14 bore against him. He got to buy lunch. My extreme spread was just a tiny bit better than his, however, mine were centered on the bullseye and had 4 in just over 1", with one flyer caused by me.

So - maybe I already have my "big Bore".