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Discussion Starter · #1 ·
Hello,
I have a 1966 or so Mossberg 500a 12 gauge that I broke the slide tube arm. I am trying to find online a source for a replacement but I am getting conflicting info. I have attached pictures of my broken slide tube assembly. Can you look at the picture and tell me the correct length? It is a single arm slide tube. There is no way to use a double arm since the receiver only has one hole for one arm. Please help me find a source to order a replacement that is in stock.

This is what Brownells has to say about it.
Prior to 1973 all action slide tube assemblies utilized tubes with a length of 7-¾". In 1993, running production changes commenced to change over to a tube with a length of 6-¾" in all gauges. The change will typically found in the Model 500's with serial number prefix K3 and Model 835's with serial number prefix UM or higher (K4, K5; UN, UO). There is an exception: All Special Purpose, Persuader and Cruiser produced to date still use the 7-¾" action slide tube assembly.

The current production 6-¾" action slide tube assembly, with appropriate forearm, may be used on models previously using the 7-¾" action slide tube. In some instances modifications will be required as noted below.

Single Arm Action Slide Tube Assemblies: Early production Model 500 shotguns utilize an action slide tube assy. (forend tube assembly.) with a tube length of 7-¾" and a single action arm. This tube assembly is obsolete. A twin bar action slide assembly with a tube of the appropriate length may be used as a replacement for the obsolete single arm action slide assembly. If both the action slide tube assembly and the forearm are being replaced, they may be replaced with either 7-¾" or 6-¾" action tube assemblies and matching forearms as available.

Thanks, Tony



 

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Mossberg told me to cut one of the action bars off the new style double action bar part, it worked great
 

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Discussion Starter · #3 ·
Chuck,
I am going to try to weld the broken piece back tomorrow morning. If it doesn't work I will order a double bar from Numrich tomorrow. Thanks for the info. Tony
 

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Discussion Starter · #4 ·
Well I was able to weld the piece back onto the end of the slide tube assembly. With a little help from my Dremel to clean up the welds I have it back together and the gun will be function tested next week. Thanks again, Tony
 

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My post from a few weeks back on the same topic;

"any two arm slide will work, just remove the one bar. It's the same basic part. It's a copper or bronze pin on most models, steel on some. Takes like five mins to pop the one arm off the modern slide tube. First caveat here is the standoff bushings. Those spiral springs on the original mag tube that keep the slide tube from rubbing the tube all over. Your original slide tube is a straight wall tube. A modern slide tube will have the dimples on the tube and those won't work with the spirals. Ideally, you'll want to find on old straight wall two arm on Ebay....still a common part. Second best, a modern dimpled slide. You'll need to either pop those spirals off the old tube and hope they didn't rust it through too bad that it can't be cleaned up....or you'll just need to buy a new mag tube. If you go new mag tube and new dimpled slide tube, you're looking at $50. Old two arm straight wall slide tube, you're looking at $25. That gun can be made whole again for not a lot of dinero, though. Well worth the effort."

A pinned action bar forearm will be a bit looser than the original welded part. It's not a detraction, though. Tack weld it if you don't like it that way. If you're all set to weld, just grab the bar from a current tube and weld it to your old tube.

Yours is a 7 3/4" (7 5/8"). Measure it from the edge of the action bar collar to the front edge of the threads. If you go for the new slide tube, measure it the same way.

Measuring your forearm to find the tube size....another post of mine;

"On the inside of your forearm, on the back side, you'll see two tiny ledges machined. Pretty close to 3/4" between the two. The action bar attach collar on the action slide tube fits there when the wood is mounted. Measure from the backmost ledge, it'll be where the slide tube back edge is, all the way to the front of the wood on your forearm. At that front, you'll find another tiny ledge just short of the front edge of the forearm itself. That'll be pretty near to where the front of your slide tube will hit, barring individual manufacturing diffs of course. So backmost ledge to frontmost ledge and you'll get your tube size."
 
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