It means you have a military firearm made by the Italian National Arms Factory in Brecia Italy, with a serial number of A9587.
Fabricated National Arsenal Brescia, serial number A3707. This is on a Carcano rifle.
Probably a serial number
The rifle scabbard and rifle should be on the fore-side (left side) with the butt toward the front at about the height of the horn of the saddle.
Gardone is the town in Brescia where the gun was produced, not the model name. Antonio Zoli 10ga guns are valued to around $600 as shooters.
Your shotgun was made by MAVI di Salvinelli , Brescia, Gardone, VT, Italy and imported by Eagle Arms of New York, NY. Both of these firms are no longer in business.
Whichever side is more comfortable
Depends on the rifle- some do not HAVE a bolt catch. On the AR15 family of rifles, it is the left side of the receiver.
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the serial number is written on the metalwork on the left hand side of the rifle.
A rifle or side arm. Mortars, rocket launchers, machine guns etc. are typically a weapons platoon or special designation within a company.
M1918 Browning Automatic Rifle .
On the left side of the receiver.