Smoke - you should be able to load to the same expansion as T-7 gave - however is some bores/calibres/barrels/loads - it gets a bit flighty - with jumpy pressure readings.

I would load up some real black powder loads to set a maximum load for pressure reading - if you want the middle 'African' load, use the 5.5dram (150gr.), or perhaps 7 dram (191gr.) for the top 2 3/4" load. There was also a 3" hull with 9 dram load for a special heavily built DR, but you will not like shooting that one - I guarantee that. The 7 dram of real black powder won't be much fun either, in a light gun. My double 12 weighed only 7 1/2 pounds - 7 drams 2F kinda hurt in BP, but not the equivalent velocity load in smokeless - 1,550fps. My first shot with 7 drams spun me around like a weathercock. I needed to hold the gun a bit more deliberately, I found. After that it wasn't really bad, just not as much fun as shooting the equivelent speeds with smokeless.

Measure the case expansion - probably new hulls are best for consistency. That should give you a max. for useable loads. It might be interesting to compare those measurements to the T7.