Looked at a Spanish shotgun from 1980s era. It is 12 gauge. On the barrels all the normal stamp are present but i has this following the weight in grams of the barrels - qmus or gmus. I haven't seen this before and haven't been able to find it in my references on Spanish proofs. Is this a proof mark or a builders mark? and what might it mean?

It is not a proof mark, it is a starting barrel weight

GMOS = grams

Example: 1400 GMOS is 3.1pounds (1400/28=50/16=3.12)

1560 GMOS is 3.5 pounds,

I use 28 grams equals an ounce.
Actually it is 1 Ounce = 28.3495231 Grams
close enough

Mike

Thanks skeettx, I knew the 1410 was the gram weight but had never seen the marks, which look more like qmus than Gmos. They are very lightly stamped on this example and rather small too. Sometimes things just don't connect. Was the starting weight of the barrels as they left the proof house or was it of the raw barrels before final striking and finish? I would assume it was after final finish as a means of knowing whether the guns were still in proof?