What is a magazine-fed shotgun? How a gas system works

One of the first distinctions you meet when buying a shotgun is how the gun feeds. On a classic semi-automatic the shells are loaded one by one into a tube under the barrel. On a magazine-fed gun they come from a detachable box magazine. Here is what that changes in practice, and how a gas-operated action works.

What does magazine-fed mean?

A magazine holds shells under spring pressure and clips into the receiver. As the fired shell is ejected, the spring lifts the next one and the action chambers it. FUMSAN's FS12 and FS20 series are offered with 2+1, 5+1 and 10+1 magazine options — the capacity of the magazine plus one in the chamber.

• Faster reloads: swapping a magazine is quicker than feeding shells individually.
• Prepared loads: a second magazine lets you change shot type immediately.
• Safer unloading: removing the magazine is the most practical way to make the gun safe at the end of a hunt.

How a gas system works

Both the FS12 and the FS20 are gas operated. When a shell fires, high-pressure gas builds inside the barrel. A small port bleeds part of that gas against a piston, which drives the bolt rearward. The bolt ejects the spent hull, compresses the spring and chambers the next shell from the magazine — all before you release the trigger.

The practical benefit is recoil: part of the energy is spent cycling the action rather than reaching your shoulder.

The maintenance side

Every shot leaves powder residue in the gas port and around the piston. On a gas gun, regular cleaning is part of how the system works, not an optional extra. When residue builds up, the gun starts failing to eject or to feed.

Slug barrel and mobile choke

Both series use a 51 cm slug barrel with a 76 mm Magnum chamber and a mobile choke. The choke is the constriction at the muzzle that controls how widely the shot spreads; an interchangeable choke lets one gun cover both close, wide patterns and tighter long-range ones.

Which series suits you?

The FS12 is 12 gauge, the FS20 is 20 gauge. Their action, barrel length, chamber and magazine options are identical — the difference is the bore. See our separate guide on choosing a gauge, and check the product pages for the current technical table and finish options.