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Old September 12, 2009, 03:11 PM   #1
drew747
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Gas operating vs inertia

Can someone give me the simple definition of the two?
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Old September 12, 2009, 03:30 PM   #2
RNB65
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In a nutshell: An inertia system uses directly recoil energy to push the bolt back and cycle the action. A gas system uses gas ports drilled through the barrel to vent propellant gases into a gas piston which pushes the bolt back and cycles the action.

Here's more detail:

http://www.chuckhawks.com/autoloadin...un_actions.htm
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Old September 12, 2009, 03:31 PM   #3
lockedcj7
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Simply put:

A gas operated gun bleeds a small amount of the propellant gasses off to cycle the action.

An inertia gun doesn't. It uses the force of the recoil to cycle the action.
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Old September 12, 2009, 04:45 PM   #4
the rifleer
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I have a question. Obviously if it is used properly, both can be very reliable, but what if you do something like use a light load and shoot with one hand from the hip or something stupid like that where then gun is going to use a lot of the recoil driving your hand back. Would an inertia operated gun still cycle properly?
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Old September 12, 2009, 05:23 PM   #5
RNB65
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Don't know. I've never tried limpwristing a shotgun. For that matter, it's been many years since I last shot an inertia operated shotgun. I imagine that if the load is light and you allow the energy to drain away with rearward movement of the gun, it may well not drive the bolt back far enough to eject the empty shell and load a new one. Similar to limpwristing a pistol.
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Old September 12, 2009, 06:04 PM   #6
Creeper
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Quote:
I have a question. Obviously if it is used properly, both can be very reliable, but what if you do something like use a light load and shoot with one hand from the hip or something stupid like that where then gun is going to use a lot of the recoil driving your hand back. Would an inertia operated gun still cycle properly?
I have a Benelli M2 Tactical. I've found that with anything other than really soft, "reduced-recoil" and "Lite" loadings, the gun will function when fired from any position... off the hip, and even one or weak-handed.
I purposely tested this aspect to confirm that I can operate the gun in any state of conscious physical condition.
I'm no expert, but it seems to be more an issue of a minimum energy requirement than of a braced or unbraced shooting position.

With Lite loadings, my gun in particular (but not all M2s I'd imagine) will fail to eject fully... which means that after the rotating bolt head unlocks, the bolt carrier almost but not quite made it fully to the rear to effect the eject function.
I've only tried Lite loadings when I was still breaking in the gun... so it's possible that after several thousands of shots, it may function successfully with many of them now.

The advantages to an inertia gun are they are typically lighter in weight than an equivalent gas gun, and that they shoot very clean and can't "gum up" like a gas gun can... a perfect all-day, every-day field or patrol gun.
The downside to inertia operation is ammo limitations and typically, greater felt recoil.
I'm not particularly recoil sensitive, so I went with the M2. If I was recoil sensitive or had a desire to shoot Lite loadings, I would have bought a heavier and gas-operated gun like the M4.

As a point of reference, my typical practice loading is B&P "Baby Magnum" which is 1.5 oz of 0.0 shot (an Italian shot equvalent to about a "1.5" bird shot) @ 1280 fps.
This is a fairly "soft shooting" ammo, all things considered, as B&P incorporates the "Gordon System" into many of their shells.

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Old September 12, 2009, 06:53 PM   #7
mwar410
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before I chronographed my 12 ga. reloads, they were just over 1050fps. shot them all the time from a 391, never had any problems. And my fore arm hand doesn't even hold the gun.
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Old September 12, 2009, 07:10 PM   #8
jaguarxk120
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I've seen postings on the Franchi forum about the shotgun not cycling properly. The owner took the gun to a gunsmith who test fired and it functioned perfectly. The owner was limpwristing the gun, not holding it to the shoulder tight enough.

During the firing cycle the recoiling barrel and breach bolt move backward locked together against the recoil spring. If not held fimly, the gun will jamb or miss feed.
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Old September 13, 2009, 07:47 AM   #9
lockedcj7
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A gas operated gun can fail to cycle properly with light loads but I don't think limp-wristing it would be a problem since it doesn't depend on resistance to function properly.

FWIW- I've had 1100s and 11-87s and some of them didn't like light loads. Some cycled them perfectly. I had a "magnum" 1100 that only had one bleed hole and it needed 3" shells to cycle properly. I swapped in a LT-20 barrel for 2 3/4" shells and it worked great. That told me that the action wasn't getting enough gas pressure with light loads and the magnum barrel.

As an aside, I have both types now and I prefer the gas guns even though they require more intensive cleaning and maintenance. If I was going to Argentina I'd take the gas gun as a primary and the inertia gun as a backup.
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Last edited by lockedcj7; September 13, 2009 at 10:39 AM.
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Old September 13, 2009, 10:33 AM   #10
B.L.E.
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If I understand correctly, the Benelli system will not cycle if you do the opposite of limp wristing, that is putting the stock against something that prevents is from recoiling. It relies on the whole shotgun moving backwards while a weight inside the bolt does not to rotate the bolt that unlocks the breech.
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Old September 13, 2009, 07:46 PM   #11
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The 11-87 I owned would not cycle light loads when fired from the hip. I have never tried it with my Benelli
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Old September 13, 2009, 08:46 PM   #12
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Quote:
If I understand correctly, the Benelli system will not cycle if you do the opposite of limp wristing, that is putting the stock against something that prevents is from recoiling. It relies on the whole shotgun moving backwards while a weight inside the bolt does not to rotate the bolt that unlocks the breech.
I'll have to give that a try sometime, to see if there's any truth to it... butt the gun up against a fence post or tree and pop a few off.

I do know that hanging a bunch of farkles like sidesaddles, some of the heavier lights, bulky optics and other tactkool trinkets can cause a M1 or M2 to not cycle properly with anything other than full power loads.

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Old September 14, 2009, 01:43 AM   #13
impalacustom
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BLE is right, the 2 piece bolt system in the Benelli needs to have the whole gun move backwards which is the whole point to their "inertia" system. If you block up a Benelli inertia shotgun to the point where the gun is unable to move it will not cycle a round. That is why there is a recoil spring and inertia spring in the Benelli, the inertia spring compresses first as the bolt head stays put for a split second while the whole gun moves back, then the spring pushes back on the bolt to cycle the action. Gas and recoil operated will cycle.

If you want to get a kick out of the Benelli sales pitch go read about their new In-Line Inertia Driven System. I didn't realize that there were gas operating shotguns in the 19th century, lol. I am stuck in the humpback era and still use yesterdays technology with no problems, even last year my humpback cycled just fine at -23*F
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Old September 14, 2009, 11:46 AM   #14
BigJimP
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In terms of light loads - my Benelli Super Sport 12ga will cycle loads down to 7/8 oz as long as they are at least 1200 fps. It will not cycle loads at 1150 fps.
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