Petrol & Powder
11-29-2015, 05:34 PM
I know this is the factory rifle section but the issue of shotgun action types came up recently on another thread and I was reminded of this issue.
Most of the folks on this forum are very knowledgeable when it comes to firearms but occasionally when speaking to someone in person it becomes obvious that they are a bit confused about action types.
One of those issues concerns the differences in semi-auto shotgun actions. I've encountered more than one person that thinks all semi-auto shotguns are gas operated. So, just for general review, there are three basic operating systems for semi-auto (self loading) shotguns.
long Recoil
gas operated
inertia
Long recoil - These are the old Browning Auto-5's, Remington model 11, Remington 11-48 and Franchi AL-48 models. There are others but those are the well known examples. In the long recoil system the barrel and bolt are locked together and upon firing, the barrel and bolt recoil together before the bolt is unlocked from the barrel. The barrel is then returned forward, the carrier lifts another round in place and the bolt is returned to battery by a separate spring housed in the butt stock. The system is mechanically complex but fairly reliable. There are no gas ports, pistons or O-rings. The majority of the hot gases and firing debris is confined to the interior of the barrel.
Gas Operation - The vast majority of semi-auto shotguns fall into this category. In a gas operated shotgun a small amount of gas is bleed off the barrel and used to drive a piston connected to the bolt carrier. Some gas systems are designed to work with light loads and vent off excessive gas pressure from heavy loads to protect the action from damage when firing heavy loads. The gas operated guns are not as complex as the long recoil systems but they do introduce hot/dirty gases into the operating system. The Berretta 300 series, Remington 1100, Remington 11-87 and Browning Gold are all examples of gas operated shotguns.
Inertia - This is the one that confuses some folks but in reality it is the simplest system. A rotating bolt head is locked to the barrel extension at the moment of firing. When the gun is fired the entire gun recoils rearward except for the relatively massive bolt carrier that remains stationary due to inertia. The gun essentially recoils past the carrier. This action compresses a large spring located between the bolt head and the carrier. When the rearward recoil of the gun slows, the energy stored in that spring is released and it drives the bolt carrier rearward. As the carrier is pushed to the rear a cam rotates the bolt head and it unlocks from the barrel extension allowing the bolt and carrier to travel rearward. A spring then returns the bolt carrier & bolt forward to chamber the next round. Most of the hot/dirty gases remain in the barrel. The Benelli shotguns are the most common users of the inertia system. The system is very simple but it does require some overall recoil motion in order to function. If the gun doesn't recoil relative to the bolt carrier there will not be enough stored energy to drive the carrier rearward and unlock the bolt.
There are some other operating systems out there, including some hybrid types but those three make up the vast majority of semi-auto shotgun actions.
Most of the folks on this forum are very knowledgeable when it comes to firearms but occasionally when speaking to someone in person it becomes obvious that they are a bit confused about action types.
One of those issues concerns the differences in semi-auto shotgun actions. I've encountered more than one person that thinks all semi-auto shotguns are gas operated. So, just for general review, there are three basic operating systems for semi-auto (self loading) shotguns.
long Recoil
gas operated
inertia
Long recoil - These are the old Browning Auto-5's, Remington model 11, Remington 11-48 and Franchi AL-48 models. There are others but those are the well known examples. In the long recoil system the barrel and bolt are locked together and upon firing, the barrel and bolt recoil together before the bolt is unlocked from the barrel. The barrel is then returned forward, the carrier lifts another round in place and the bolt is returned to battery by a separate spring housed in the butt stock. The system is mechanically complex but fairly reliable. There are no gas ports, pistons or O-rings. The majority of the hot gases and firing debris is confined to the interior of the barrel.
Gas Operation - The vast majority of semi-auto shotguns fall into this category. In a gas operated shotgun a small amount of gas is bleed off the barrel and used to drive a piston connected to the bolt carrier. Some gas systems are designed to work with light loads and vent off excessive gas pressure from heavy loads to protect the action from damage when firing heavy loads. The gas operated guns are not as complex as the long recoil systems but they do introduce hot/dirty gases into the operating system. The Berretta 300 series, Remington 1100, Remington 11-87 and Browning Gold are all examples of gas operated shotguns.
Inertia - This is the one that confuses some folks but in reality it is the simplest system. A rotating bolt head is locked to the barrel extension at the moment of firing. When the gun is fired the entire gun recoils rearward except for the relatively massive bolt carrier that remains stationary due to inertia. The gun essentially recoils past the carrier. This action compresses a large spring located between the bolt head and the carrier. When the rearward recoil of the gun slows, the energy stored in that spring is released and it drives the bolt carrier rearward. As the carrier is pushed to the rear a cam rotates the bolt head and it unlocks from the barrel extension allowing the bolt and carrier to travel rearward. A spring then returns the bolt carrier & bolt forward to chamber the next round. Most of the hot/dirty gases remain in the barrel. The Benelli shotguns are the most common users of the inertia system. The system is very simple but it does require some overall recoil motion in order to function. If the gun doesn't recoil relative to the bolt carrier there will not be enough stored energy to drive the carrier rearward and unlock the bolt.
There are some other operating systems out there, including some hybrid types but those three make up the vast majority of semi-auto shotgun actions.