12 ga. has a far more diversified variety of shells (loads) than 20 ga. If you don't want to reload, there are many shell types to choose from. Bigger, hotter, faster 12 ga. loads are best for bigger, tougher or faster birds such as ducks, geese and turkeys. 12 is necessary with buckshot or slugs for deer in some places. 20 ga. is better for smaller birds such as pheasant, grouse, woodcock and snipe. 20 is OK with slugs for deer. Both are used in shooting games like trap, skeet and sporting clays and I use both. 1 ounce of shot pellets is exactly the same quantity from either size shotgun. The gauge refers to the barrel diameters where that is the number of lead balls, fitting into the barrel, which weigh 1 pound (16 ounces).
Gauge is the term that comes to mind, such as 12 gauge (ga.) wire. With plastic bags, one might use mil, such as a 3 mil garbage bag. "Mil" indicates thousandths of an inch.
Excelsior shotguns were mfg. in Europe by Liegeoise D'Armes a Feu. The Excelsior name was also used in the US by Iver Johnson Arms and Cycle works
Go to Gunbroker.com and do a search for Bost and you will come up with at least two shotguns like yours that are for sale, and will provide some information on the shotgun itself.
Around $150.
There isn't one
12 gauge shells.
There are many different models of 12 gauge shotguns for sale at online retailers like Amazon and GunBroker. One can also check online at eBay for 12 gauge shotguns which are for sale or trade.
Remington has made many thousands of 12 gauge shotguns in dozens of different models/configurations.
12 has a bigger bore.
No.
Crescent
These shotguns came in 20, 28, 16, And 12 gauge calibers
Remington 12 gauge 3" "OO" Buckshot and Rifled slug
You can't
The lower the gauge the heavier, sheet metal, wire & shotguns...
What model is it? Need more infor as Browning has several different types of shotguns.
Numerous companies in many countries have made single shot 12 gauge shotguns.