Originally Posted By: "PeteM"
Miller,
The nitro proof mark was introduced in 1898 for military arms. They started using it for all arms in 1903.

That is essentially what I said. Only difference is info I have would indicate that in 1903 Smokeless proof for shotguns was still considered an option in Belgium so it will not necessarily be found on "ALL" shotguns. It was thus used only on those arms requiring or requesting smokeless powder proof at that point in time.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra