Idea for a gas operation - Page 3

Dixie Gunsmithing · February 27, 2015, 09:25 PM

James, has anyone tested the Benelli inertia system in a non-recoiling jig, or fouled the stock against anything, to see what happens when it's shot?

I know that without the receiver recoiling reward, and the rear of the bolt momentarily staying stationary, the bolt can't twist its rotary breech lock, more closed, I guess one could say, however, it is still locked. Also, without the recoil, due to the gun being held stationary, there's no force to drive the bolt back, against the weak bolt spring, for cycling. The more I thought of this system, my guess is, that it would fire, and just not cycle, instead of the bolt opening.

James K · February 27, 2015, 09:53 PM

I don't know what would happen if the butt of the gun were placed, say, against a tree. But then that is not the way the gun is supposed to be used, so it is like asking what would happen if the barrel of an Auto 5 were clamped in a vise. (The gun wouldn't work, but so what?)

Remember the cycle, though. The recoil drives the gun back while the heavy bolt carrier tries to remain stationary. That compresses the very strong spring between the bolt and the carrier. When the recoil force dissipates, the spring reasserts itself, and throws the carrier to the rear, camming the bolt open and bringing it along for the ride. There is enough force in that heavy spring to complete the carrier/bolt movement to the rear, at which point the return spring works, as in most semi-autos, to return the whole thing to battery.

That heavy spring is the key to the whole thing, but it just doesn't look like it can do all that it does. And for reasons that are not clear, Benelli seldom describes or pictures what actually happens, apparently preferring to keep it something of a mystery. To further complicate things, the inertia operated guns are only part of Benelli's line which also includes conventional gas guns and over/under guns.

Jim

Dixie Gunsmithing · February 27, 2015, 10:26 PM

The problem I see, for the inertia system, would be acceptance by the military, especially if a gun wouldn't cycle if fouled from recoiling. Say if a soldier was laying flat of his back, and the stock of the gun was on the ground. Then, while trying to fire up at his opponent, he would get one shot off, then be done. Of course they should be trained to know this, but I can envision several circumstances where a conventional action would be better. Thus, would the inertia system have any benefit to a rifle, other than sporting?

On the bolt, it's not just the bolt spring that causes it to cycle, but the overcome forward inertia, as by what I have read, the recoil is still happening when the spring expands back, so the weight of the bolt is driven rearward by the recoil too, and since the return spring is weak, the bolt has enough force to cycle it. I bet a recoil reducer would affect the cycling too, over this, since they work on the inertia basis also.

James K · February 28, 2015, 03:30 PM

The bolt won't be driven back by recoil; it tries to stay where it is. It has to be moved back by an outside force.

For the reasons you state, the Benelli inertial system would probably not be adapted to a military rifle and as far as I know there are no proposals to do so. It might work in a rifle, but so far Benelli has used it only in a pistol (I have one) and shotguns.

The return spring does not need to be very strong; the A5 is an example of a strong recoil spring and a fairly weak return spring. In the Benelli, that small but strong spring inside the bolt really gives the carrier a heckuva kick. (It doesn't take a lot of movement; look at the M1 Carbine, where the piston moves about 1/8 inch, yet that is enough to kick the operating slide and bolt back and extract the case.)

Jim

Gunplummer · February 28, 2015, 04:33 PM

45 auto----Most were when I was in the Marines, but I hit a lot of these re-works in what I would call "Secondary" military posts later when I was in the Army. It is easy to see when M-16's were reworked. It is amazing what pops up in some out of the way posts. When I was in Germany (Army) a couple of us representing all the different repair sections went around to different warehouses and identified piles of parts that had lost the stock # identification. It was unbelievable what turned up. You have to remember that some branches did not really "Buy" new equipment. I remember when the Army "gave" the Marines their outdated M60 series tanks. I have no idea if it was considered a purchase by the Marines or not. Anyway, even in the late 70's it was not unusual to find plenty of 1911's in units in Europe. I distinctly remember coming across an M-2 .50 made by colt with a 4 digit serial #. It had oval slots in the barrel support, which was odd. Sometimes when they consolidate a couple of units into a smaller one for an area the units leaving "Donate" some of their equipment to make up the new unit. Guess what the old units get rid of?

James K · February 28, 2015, 09:59 PM

Since a discussion of the Benelli got started on this thread, here is Benelli's own video showing how the shotgun works. Watch the large spring carefully to see that the return spring does not compress it, but recoil does once the shot is fired. Then when the recoil force dissipates, the heavy spring re-asserts itself and drives the bolt carrier back, a cam turning and unlocking the rotary bolt head.

https://www.youtube.com/watch?v=2UOSB8mwwlQ

Jim

Dixie Gunsmithing · March 1, 2015, 12:48 AM

Jim,

It shows what I've spoken of and read. The inertia spring action, in the bolt, happens for only part of the recoil cycle. When the spring uncoils, it starts the bolt rearward, but the recoil is also going in that direction too, which is countering to the bolt, however, the recoil speed is slowing down, where it will soon stop. The speed the bolt travels overcomes this, due to the recoil slowing down and the springs kick, so the slowing recoil helps it along, and when the gun slows to a stop, on the shoulder, the gun reverses direction, due to the shoulder, and goes forward again, increasing the speed the bolt has going back, until it goes as far as it can, then cycles with the bolt follower spring, (or stays back, due to no new round to release it). The bolt may reach its full rearward stroke, before the shoulder stops the gun, and the muscles cause it to go forward again. That I do not know, and it's not shown. Either way would work.

The cycle is similar to a cue ball, sitting stationary, which is driven against the rail of a pool table, over the sudden movement of the table shifting under it, where the cue ball would then change direction, after it meets and compresses the rail, which sends it backwards. However, in this case, the table would be moving, (recoiling), in the same direction as the reversed ball, which wouldn't work well, unless the tables motion had the brakes applied to it, (the shooters shoulder), slowing it down. It wouldn't work at all, though, if not for the recoil, (or moving table), to set it all in motion.

James K · March 2, 2015, 02:21 AM

I think that bolt carrier* moves back so fast under the impulse of the spring, that the continued movement of the gun in recoil is not significant. Even if it were, it should affect any autoloading shotgun. In a gas gun, the bolt is moving back while there is still recoil force, so it should have the same problem if that problem is there. If the shoulder were padded enough I suppose you could have something equivalent to "limp wristing" but I think a shotgun is heavy enough in itself that that wouldn't happen.

*I am calling the rear part of the bolt the bolt carrier because that is how it acts. The rotating bolt head is really the bolt and the carrier cams it into and out of the locked position, pretty much like an AR-15.

Jim

February 27, 2015, 09:25 PM	#51
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	James, has anyone tested the Benelli inertia system in a non-recoiling jig, or fouled the stock against anything, to see what happens when it's shot? I know that without the receiver recoiling reward, and the rear of the bolt momentarily staying stationary, the bolt can't twist its rotary breech lock, more closed, I guess one could say, however, it is still locked. Also, without the recoil, due to the gun being held stationary, there's no force to drive the bolt back, against the weak bolt spring, for cycling. The more I thought of this system, my guess is, that it would fire, and just not cycle, instead of the bolt opening.

February 27, 2015, 09:53 PM	#52
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	I don't know what would happen if the butt of the gun were placed, say, against a tree. But then that is not the way the gun is supposed to be used, so it is like asking what would happen if the barrel of an Auto 5 were clamped in a vise. (The gun wouldn't work, but so what?) Remember the cycle, though. The recoil drives the gun back while the heavy bolt carrier tries to remain stationary. That compresses the very strong spring between the bolt and the carrier. When the recoil force dissipates, the spring reasserts itself, and throws the carrier to the rear, camming the bolt open and bringing it along for the ride. There is enough force in that heavy spring to complete the carrier/bolt movement to the rear, at which point the return spring works, as in most semi-autos, to return the whole thing to battery. That heavy spring is the key to the whole thing, but it just doesn't look like it can do all that it does. And for reasons that are not clear, Benelli seldom describes or pictures what actually happens, apparently preferring to keep it something of a mystery. To further complicate things, the inertia operated guns are only part of Benelli's line which also includes conventional gas guns and over/under guns. Jim

February 27, 2015, 10:26 PM	#53
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	The problem I see, for the inertia system, would be acceptance by the military, especially if a gun wouldn't cycle if fouled from recoiling. Say if a soldier was laying flat of his back, and the stock of the gun was on the ground. Then, while trying to fire up at his opponent, he would get one shot off, then be done. Of course they should be trained to know this, but I can envision several circumstances where a conventional action would be better. Thus, would the inertia system have any benefit to a rifle, other than sporting? On the bolt, it's not just the bolt spring that causes it to cycle, but the overcome forward inertia, as by what I have read, the recoil is still happening when the spring expands back, so the weight of the bolt is driven rearward by the recoil too, and since the return spring is weak, the bolt has enough force to cycle it. I bet a recoil reducer would affect the cycling too, over this, since they work on the inertia basis also.

February 28, 2015, 03:30 PM	#54
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	The bolt won't be driven back by recoil; it tries to stay where it is. It has to be moved back by an outside force. For the reasons you state, the Benelli inertial system would probably not be adapted to a military rifle and as far as I know there are no proposals to do so. It might work in a rifle, but so far Benelli has used it only in a pistol (I have one) and shotguns. The return spring does not need to be very strong; the A5 is an example of a strong recoil spring and a fairly weak return spring. In the Benelli, that small but strong spring inside the bolt really gives the carrier a heckuva kick. (It doesn't take a lot of movement; look at the M1 Carbine, where the piston moves about 1/8 inch, yet that is enough to kick the operating slide and bolt back and extract the case.) Jim

February 28, 2015, 04:33 PM	#55
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	45 auto----Most were when I was in the Marines, but I hit a lot of these re-works in what I would call "Secondary" military posts later when I was in the Army. It is easy to see when M-16's were reworked. It is amazing what pops up in some out of the way posts. When I was in Germany (Army) a couple of us representing all the different repair sections went around to different warehouses and identified piles of parts that had lost the stock # identification. It was unbelievable what turned up. You have to remember that some branches did not really "Buy" new equipment. I remember when the Army "gave" the Marines their outdated M60 series tanks. I have no idea if it was considered a purchase by the Marines or not. Anyway, even in the late 70's it was not unusual to find plenty of 1911's in units in Europe. I distinctly remember coming across an M-2 .50 made by colt with a 4 digit serial #. It had oval slots in the barrel support, which was odd. Sometimes when they consolidate a couple of units into a smaller one for an area the units leaving "Donate" some of their equipment to make up the new unit. Guess what the old units get rid of?

February 28, 2015, 09:59 PM	#56
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	Since a discussion of the Benelli got started on this thread, here is Benelli's own video showing how the shotgun works. Watch the large spring carefully to see that the return spring does not compress it, but recoil does once the shot is fired. Then when the recoil force dissipates, the heavy spring re-asserts itself and drives the bolt carrier back, a cam turning and unlocking the rotary bolt head. https://www.youtube.com/watch?v=2UOSB8mwwlQ Jim

March 1, 2015, 12:48 AM	#57
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	Jim, It shows what I've spoken of and read. The inertia spring action, in the bolt, happens for only part of the recoil cycle. When the spring uncoils, it starts the bolt rearward, but the recoil is also going in that direction too, which is countering to the bolt, however, the recoil speed is slowing down, where it will soon stop. The speed the bolt travels overcomes this, due to the recoil slowing down and the springs kick, so the slowing recoil helps it along, and when the gun slows to a stop, on the shoulder, the gun reverses direction, due to the shoulder, and goes forward again, increasing the speed the bolt has going back, until it goes as far as it can, then cycles with the bolt follower spring, (or stays back, due to no new round to release it). The bolt may reach its full rearward stroke, before the shoulder stops the gun, and the muscles cause it to go forward again. That I do not know, and it's not shown. Either way would work. The cycle is similar to a cue ball, sitting stationary, which is driven against the rail of a pool table, over the sudden movement of the table shifting under it, where the cue ball would then change direction, after it meets and compresses the rail, which sends it backwards. However, in this case, the table would be moving, (recoiling), in the same direction as the reversed ball, which wouldn't work well, unless the tables motion had the brakes applied to it, (the shooters shoulder), slowing it down. It wouldn't work at all, though, if not for the recoil, (or moving table), to set it all in motion.

March 2, 2015, 02:21 AM	#58
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	I think that bolt carrier* moves back so fast under the impulse of the spring, that the continued movement of the gun in recoil is not significant. Even if it were, it should affect any autoloading shotgun. In a gas gun, the bolt is moving back while there is still recoil force, so it should have the same problem if that problem is there. If the shoulder were padded enough I suppose you could have something equivalent to "limp wristing" but I think a shotgun is heavy enough in itself that that wouldn't happen. *I am calling the rear part of the bolt the bolt carrier because that is how it acts. The rotating bolt head is really the bolt and the carrier cams it into and out of the locked position, pretty much like an AR-15. Jim