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How does inertia system work?

4697 Views 5 Replies 4 Participants Last post by  wwb
I know that Benelli, for instance, and at least one Beretta use inertia systems in their autoloaders. They seem touted for having few moving parts and good reliability. Anyone know how these things work? I know the ins and outs of a gas gun, but I can't easily picture the mechanism behind these guns. I obviously don't own any. Just curious.
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I've seen diagrams with brief explanations in the Benelli advertisements many times. However, I probably don't remember it well enough to describe it here. Try the Benelli website.

Ah, what the heck. I'll take a stab at it from memory. If I'm wrong, I'm sure that someone will be along shortly to correct me. When you fire a round, the gun recoils. The rearward movement of the gun causes a coil spring in the bolt to compress due to the "inertia" of the bolt resisting the rearward movement. Then the bolt unlocks and moves rearward in relation to the receiver due to the stored energy in the compressed spring. This causes the empty shell to be ejected. The hammer is also cocked on the way back. Then the spring in the bolt compresses again (due to the inertia of the moving bolt) when it hits the end of it's travel (near the rear of receiver). This compressed spring provides the stored energy to return the bolt forward, picking up the new round on it's way.

How's that? Hopefully I'm right, but even if I'm wrong, I should get an "A" for creative writing, right? :wink:
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Hey Ulysses,
Sounds good to me...I even checked your spelling.
Jay G.
Ulysses -

If you want to really polish up your creative writing, explain the A-5
Explain the A-5? :?: Piece of cake, my man. :wink:

The Browning A-5 is John Browning's design of the long recoil operated autoloading shotgun. This design is approximately 100 years old. It is called "recoil" operated (as opposed to "gas" operated) because the recoil of the shell pushing on the bolt face actually supplies the power to cycle the action.

Let's start with a loaded gun. Pull the trigger and the shell fires. The bolt is locked to the barrel extension via a recess in the barrel extension at the top of the bolt. The recoil impulse of the shell pushes against the bolt face causing the bolt and entire barrel to move rearward. At the same time this is happening, a ring welded to the bottom of the barrel and fitted around the magazine tube moves rearward with the barrel. This ring compresses the recoil spring which is around the outside of the magazine tube. After a short distance of traveling together, the bolt and barrel separate with the bolt continuing to travel to the rear and ejecting the empty shell. Once the bolt reaches it rearmost point, the recoil spring has been fully compressed. The recoil spring then releases its stored energy driving the bolt and barrel forward and picking up a new round supplied from the magazine tube via the carrier. This shell is pushed into the chamber and the bolt and barrel then lock up again ready for the next cycle. The friction ring around the magazine tube serves simply to regulate the speed at which the bolt and barrel travel to the rear. Too much speed and the gun gets battered too hard. Too little speed and the bolt doesn't have enough energy to complete the reloading cycle.

How's that? :lol:
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Excellent work!!! You get an "A" on your essay.

You would have gotten an "A+" if you had remembered to mention that they sound like a steam-powered threshing machine when they cycle, with all that chunking and clanking going on.
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