I've been thinking about a solution for retaining the mag cap on 870 express models where the dimples have been removed and the barrel lacks the old-style detent. The concept shown above is to prevent mag cap rotation via pressure from a compressed rubber plug which grips the inside of the mag tube near the end. The rubber plug is compressed when the sling stud screw is tightened after screwing the mag cap onto the mag tube. The stud screw presses the nut into the metal washer which presses against the shortened spring cap from a dimpled 870 express. The spring cap press against the teeth on the inside of the mag cap just like it did with the dimpled mag tube. The stud screw is tightened enough that the rubber plug is compressed and expands until it presses against the inside of the mag tube. The friction of the rubber plug prevents rotation of the spring cap which prevents rotation of the mag cap. The metal washer provides even pressure on the rubber plug and also prevents the mag spring from pressing against the rubber plug.
If the sling stud (or ordinary machine screw) is used, the nut and metal washer will have to be connected somehow to prevent rotation of the nut. I'd use a nutplate, but those are expensive and this needs to be cheap and easy to make. Also the rubber plug must not rotate against the shortened spring cap or washer.
One alternate way of compressing the rubber plug uses a cam lever (like used on better bicycles for quick removal of the wheels only smaller) instead of the sling stud. That would also avoid having to secure the nut to the metal washer. The downside is I have no clue where to find a small cam lever attached to a machine screw.
Thats my concept, anyone have ideas for improvement or specific materials?
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