Here's WW Greener's views on the subject at the time, from 'The Gun and Its Development':

The Double 4-bore with 20-inch barrels weighs 14 to 18 lbs; charge weight 12 to 14 drams; spherical ball 1510 grains.
Most were smooth-bore for use up to 60 yds max.

Double 8-bore:
Paper-Case Rifle: spherical ball 1092 grains.
Brass-Case Rifle: conical ball 1310 gr.
Gun weight: 20-inch barrels 11 1/2 lbs; 24-inch barrels 15 lbs.
Charge weight 10 drams, up to 12 drams with spherical ball.

A Greener 8-bore shot at the 1883 Field Rifle Trials with 10-dram load and spherical ball weighed 'only' 13 lbs.

This table of recommended bore-gun weights is presented:

It appears that Greener varied the gun-weight according to barrel-length, rather than charge weight. It is not clear whether the gun-weight dictated the barrel-length, ie if a customer specified an 11-pound 10-bore, then he got 26-inch barrels whether he liked it or not!

More to follow.....