"Normally" chamber dimensions are identical regardless whether the gun was inteded for Brass or Paper hulls. Those made especially for use with brass cases usually have an oversize bore as the walls of brass cases are thinner than paper ones & call for oversize wads.
The gun I mentioned with the prw 1887 marks is not marked "Not For Ball" either, but it is cylinder bored in both barrels so that mark would not have applied.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra