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Shotgun Feeding Tubes - Control

Discussion in 'Shotguns' started by mnrivrat, Nov 20, 2005.

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  1. mnrivrat

    mnrivrat Member

    Dec 24, 2002
    Shell Feeding Control - Pumps & Auto's

    There are two major players (parts) that control the feed of a shotgun shell from the magazine . This is true for both pump and auto shotguns that use a tube magazine.

    There are several simular names used for these parts , but for the purpose of this little story I will call them the cartridge stop and the cartridge interuptor.

    Purpose & discription: The purpose of the cartridge stop is to retain the shells in the magazine tube until the feed function calls for their release into the action. The cartdridge stop is a metal part that has a leading edge that makes contact with the base of the shell case to retain it from coming rearward out of the tube when the gun has it's bolt forward at rest .

    The purpose of the cartridge interuptor on the other hand is to prevent a second shell from feeding out of the tube during the feeding function of the previous shell.

    So lets start the feeding cycle and see how it works: The magazine is full of shells that are under spring tension pushing them rearward against the cartridge stop. As the action starts its rearward travel it activates the cartridge stop, moving it out of the way and allowing a shell to move to the rear to be picked up by the shell lifter. As the action continues rearward , and before the first shell clears the feed tube, the cartridge interuptor is activated moving its forward edge into a blocking position at the rear of the magazine tube. This prevents the next shell from prematurely feeding out of the magazine tube. The action reaches its full rearward travel ,and as it begins coming forward it picks up the lifter, moving the first shell upward for the bolt to feed it into the chamber. As it continues forward the cartridge stop moves back into positon , and as the forward travel continues, the cartridge interuptor moves back out of it's blocking position allowing the next shell to move slightly rearward from the magazine tube and coming to rest on the cartridge stop as the first shell is chambered.

    Different guns use different ways of activating the cartridge stop & cartridge interuptor ,but the functional purpose remains the same.

    Examples : The Remington 870 stop & interuptor are acted upon by the operating rod arms. Each arm has a ramp that makes contact with small tabs on the front part of the stop and the interuptor to control their in and out motion during the feeding cycle.

    On the Mossberg 500 the cartridge stop is controled by the left action arm in much the same manner as the 870 , but the interuptor is controled by the bolt carrier acting on a vertical protusion on the rear section of the interuptor arm. In the case of the 870 the interuptor head is moved horizantaly to make contact. And in the case of the 500, the interuptor is pivoted up and down to perform its function.

    Each gun has its own design - they all work well when clean, properly adjusted and not worn out.

    Bottom Line : If you are having trouble with a shell being released from the magazine, then look at the function of the cartridge stop . If you are having trouble with multiple feeding out of the magazine , then look at the function of the cartridge interuptor .
    Last edited: Nov 21, 2005
  2. sm

    sm member

    Dec 22, 2002
    Between black coffee, and shiftn' gears
    Thank you!

    Another excellent write up!
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