The HUSKY 16 bore I had ran 2 5/8" for the chambers. Thus, new Federals were 1/8" too long once fired. They actually shot well - however, if they'd have been 1/4" to long, I'd not have used them.

The Brass I bought from Buffalo Arms, was 2.4" - they fit just fine & shot well with paper wads, shot and BP.

In my MOST HUMBLE opinion (that's a joke, btw nothing humble about it, most of the time) the 16 bore rifle is perfectly balanced for NA large game shooting - all of it, with round ball. Ed Rayle makes his 16 Bore barrels at .670" (bore dimension) so the standard .662" Lyman mould is the right size.
.670" is 1/2 way between the 16 and 15 bore sizes.