Thanks dougk and Drilling Man for your assistance.
I was being careful to avoid barrel heating, as I knew that I had a very limited amount of ammo and wanted to make it count.  I had pretty much resigned myself to sighting in for one barrel and just using Kentucky windage for the second shot if it was needed.  I couldn't find anything on the gun indicating recommended bullet weight.
I wasn't totally happy with things so I passed on using the gun for hunting this year.
I tried a few more boxes of various brands/weights of ammo that I was able to scrounge at local shops ("You want a box of what?") and gun shows with various results.  Then at a local gun show recently I picked up two boxes of Fiocchi 170gr loads.  WOW!  Two shots from each barrel produce two 1 1/4" groups that OVERLAP at 100 yards!  By the time I got them sighted in I had only 23 rounds left.  I am hoarding them for next year's hunting season.  I have a trip planned to Quebec for caribou, my first time for these critters.  The Zoli will be my second gun (that has such a cool sound to it!).
I'm thinking of disassembling one of these priceless gems for some clues as to what kind/weight of powder they are loaded with.  Best of all, my favourite local shop thinks that they can get me more.  Until they do, or until I can dupllicate this load, I don't dare play around at longer ranges.  So for the time being, I'm going to consider this a 125-150 yard gun at maximum.  That's okay, I'm not real big on long range shooting, I'm a .45-70 fan.
Life is good.  

    Thanks again for your help.
John