If you look at the pictures you will see that "Kg" is stamped in front of "1,350". 1,350 is just a hair less than 3 pounds. Would 3 pounds sound about right for this set of barrrels?
As for the "190" shown in one picture, the complete number is depicted in another as "21190 (proof market) RAG". Does this gun have a serial number elsewhere on the receiver and does 21190 match that number or is that the single place where a serial number was stamped?
Here is something about what appears to be an Italian gun some of the same markings on the barrels, even if the barrels appear to be German. The bottom of the barrels is stamped RAG 20866".
http://www.shotgunworld.com/bbs/viewtopic.php?t=22288
Here is something else I located from a Greek:
sorry for my english my friend im from greece
i have aRINO GALESI-RIGARMI-BRESCIA TWO BARREL SHOTGUN
THE GUN IS ENGRAVED THE BARRELS IS WRITEN FLUSS STAHL
KRUPP ESSEN AT THE BOTTOM HAS THE MARKS 24830 NITO RAG PSF XVIII
KG 1.375 18.2 17.4
20.3-70 18.2 17.5
THE GUN IS IN VERY VERY GOOD CONDITION IT HAS EXTERNAL HUMMERS AND IT SHOOTS GRATE IN 12 GAUGE
http://www.gunvaluesboard.com/i-wou...rino-gallsi-rigarmi-brescia-it...-804064.html
Here, I am thinking that the KG 1.375 is the weight of the barrels and 18.2 is the gauge in mm. Could 17.4 and 17.5 be the respective barrels' inner diameters as constricted? That sounds like a lot to me. What if the 18.2 is the outer diameter of each barrel and 17.4 and 17.2 are there inner diameters as bored?
20.3mm would be the diameter of the chambers and 70mm their length. My Remington 12 gauge hull roughly measures the same.
Using Zippy's date code the barrels were proofed in 1962.
Sloppy me. I just scrolled down and saw the markings on the second barrel of the OP's gun. The barrel pictured at the bottom of the picture, assuming I am correct above, notes the length of the chamber, including room for the opened crimp., to be 70 mm. The 18.6 is the chamber's diameter in millimeters. If the Greek is correct and 20.3mm is 12 gauge, would 18.6mm be a 16 gauge chamber?
Both barrels, carrying my interpretation of the other gun's markings forward, are marked 17.1 for 17.1 mm. The 16.1 and 16.5 are the inner diameters of the barrels at their choke point. The nominal constrictions are 1mm and .6mm or .039" and .024" (which I beleive would be full and modifieds as PetahW writes).
In sum, I think you have a 16 gauge built in Italy in 1962 that takes modern 2-3/4" ammunition. One barrel has a fixed full and the other a fixed modified.
WARNING! This is all my late night rambiling and during the day I don't know what I am talking about. Maybe the guys here can make sense of my jiberish. One thing, DO NOT RELY ON MY THOUGHTS in deciding what to shoot in your gun. Take it to a qualified gunsmith to ensure what it is, what ammo it shoots, and if it is safe to shoot, before firing it.