As I recall they are about 4" but you can determine easily enough what is needed by this method. Start sticking rounds into the magazine until no more will go. Then measure how much of the next shell will go in. Add up that length and the length of the shells that went in that were more than two and cut the plug a hair more than that. Add it and verify it will then hold only two in the magazine. If I had a clue where to find one I'd measure a plug for you but I've not had one in a gun in so long I'd not even know where to look.