Mag tube won't screw into receiver on 500A

Discussion in 'Firearm Maintenance, Safety And Troubleshooting' started by Bridgebuster, Oct 4, 2017.

  1. Bridgebuster

    Bridgebuster Copper BB

    I have an older 500A combo pak (18" barrel and 28" barrel, walnut stock and pistol grip, from early 80s. I also bought a new 500 and conversion kit to build what amounts to one of the new Shockwave 14" before they actually released the Shockwave already setup.
    I decided I would like to put the new 18" barrel, WITH HEAT SHIELD, and its magazine tube onto the older 500A. Got everything disassembled and to my distress the new 500 mag tube would not screw into the older 500A receiver. The threads on both the older and newer mag tubes looks exactly the same to me. I took a plastic pick and chased the threads on both mag tubes and the older receiver just to be sure no crud was holding up the works. The new mag tube will begin to thread but then stops for some reason. I don't want to force it lest I cross-thread something.
    Is it possible the new mag tube is bigger (thicker) than the older receiver? I've read that this is a compatible swap. The old mag tube will screw right onto the old receiver but the new tube just won't Any ideas would be much appreciated.
  2. RichardL

    RichardL .410

    Turn the tube *backwards* til you hear and feel it click into the threads....that guarantees you won't cross thread. Once it starts, insert your finger into the receiver and push the mag follower up into the tube and then finish the mag tube screwing in. The follower often blocks the tube if you don't.

    Welcome to the forum, BB!
  3. Bridgebuster

    Bridgebuster Copper BB

    Thanks RichardL. I thought about that and took the "guts" out of both mag tubes; same problem. The original tube goes into the older 500A smooth as silk. The newer 500 (longer) mag tube goes in a turn and a half and just stops. Refuses to go any further and I'm extremely reluctant to try to force it. I've tried lubing the threads to see if stiction is the problem . . . no go. I have no idea why it would act like this. I thought it would be a really easy swap. Not the first time I've been wrong. :)
    Any ideas on what to do next? Would the folks at Mossberg answer if I could find a way to reach them?
    Thanks for any additional help.
  4. old mossy

    old mossy Global Moderator Staff Member Global Moderator Forum Moderator

    Sorry to hear about your problem.

    Sounds like it's got some bad threads.

    Is the mag tube you are having a problem with brand new? If so send........
    Joseph Zakher

    an email explaining your problem.

    Mention you are a member here and they might send you a new one. ...?????
  5. Bridgebuster

    Bridgebuster Copper BB

    Thank you brother. What a wonderful asset this forum is! I'll certainly give it a shot, and report back what happened.

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