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Let's Talk Benelli Inertia Bolt System


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The operation of the inertia bolt system, like the M1 & M2, is ingenious in its simplicity. Here's some information and illustrations of just how it works and explains why malfunctions of the cycling action may occur when too many accessories are attached to the gun or the gun is not properly held.


Here we go.


The accompanying text to the my diagram, in case it is not clear in the photo.


1. Ready to fire position. Bolt head is in full battery; it is important to understand that the mass of the bolt is NOT rigidly locked to barrel-receiver, the bolt-head is!


2. Upon firing, the firearm recoils backwards into the shooter's body. The inertial mass, i.e. bolt, remains stationary. The bolt head remains instantaneously locked to barrel. The rearward force of the barrel-receiver compresses the spring into the still stationary inertia mass (bolt). Because the bolt is stationary but the bolt head lugs / barrel is moving rearward, the bolt head rotates by its cam surface within the stationary bolt and thus unlocks itself from the barrel lugs; the bolt head remains fully compressed against the front of the bolt.


3. The compressed inertia spring contains all the necessary energy to cycle the action; it now expands transferring its energy to the bolt moving it rearward (as now both bolt and gun are moving rearward). The action link spring is just beginning to be compressed, retarding the rearward bolt movement to allow time for the shot charge to exit the muzzle before the breech is fully open. The energy contained in the inertia spring also has to extract / eject the cartridge and cock the hammer spring.


4.The bolt is arrested in its fully rearward position and begins to move forward (with the rest of the gun) by the force of the expanding action recoil spring, pushing the next cartridge on the carrier into battery and again and locking the bolt head by rotation into the barrel lugs.


5. The shooter recovers from the shot, moving the firearm forward into position for the next shot.



Caveats regarding this inertia mechanism:

1. The weapon MUST be free to sufficiently recoil about the bolt for this mechanism to work i.e. not secured in a rest or butt stock held against rigid ground.

2. Accessories that add too much mass to the gun can cause action cycling malfunctions.





Edited by benelliwerkes
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