I guess my Google-Fu is getting weak. I just can't find one of these anywhere online.
I want to put a sling on my Mossberg 20GA 500C, and need this gadget to attach the sling to the magazine tube or barrel.

Any help would be appreciated.

Here's one that claims to be a universal barrel/magazine tube clamp mount for a sling swivel.

http://www.impactguns.com/tacstar-b...ng-swivel-stud-1081172-751103011720.aspx

that might do it. I'll call them tomorrow. Thanks

Uncle Mike's has a set just made for that -
It has a short threaded stud that screws into a pre-tapped hole in your magazine cap. At least the ones that I have were pre-tapped. IIRC it is a NF (fine) thread. If the cap isn't tapped, it can be drilled and tapped for one.
The rear stud is has a regular wood screw thread.
Makes for a really neat looking installation.

Myron

Here's another one that's similar to your's but it's a complete replacement end cap for the magazine tube w/sling swivel stud for Mossberg 500 12, 16, 20 gauge.

http://www.midwayusa.com/product/15...erg-500-maverick-88-12-16-20-gauge-black