Merkel offered a set trigger option for their small caliber doubles fairly recently, 9.3x74 and down (don't know if they still do

). Cape Outfitters had a few of these some years back, but I haven't seen any for sale in the US in the last few years.

For a short time I had a Continental Arms 450 3.25"NE that had set triggers front and back. It was an unusual rifle in that it was under 8 1/4 pounds (in fact if I recall correctly, it may have been closer to 7 3/4). Unfortunately, the groove diameter was under .454.

Jim