I've got ZB down as 1974 taken from Nigel Brown's book.
I'll agree that 3 Drams plus 1 1/8th. ounce is a meaty load. 2 3/4 Dram and 1 ounce shoots sweet and you will find it all you need. For clays I just use 2 1/2 Dram to 7/8th. ounce. That stamping is for the Maximum service load rather than the recommended one.
Owen, two things to consider. If someone sends in a BP proof gun for re-proof they will just re-proof for BP unless Nitro Proof is specified. It may be that the Proof House upon examination did not consider it would pass re-proof for Nitro and would recommend that it only be submitted for BP proof. They will offer guidance and support on the decision which they base on over 200 years of experience. I think the 'Scotty' doctrine here may be appropriate; 'I dinna like to push her Jim she may blow'. Lagopus.....
