http://www.shotgunworld.com/bbs/viewtopic.php?f=118&t=197756You can do a home remedy of installing a "soda can shim," as described in the informational link above. "Worth messing with...?" Yes.
From what I've researched, folks at Remington feel the best that you can expect from a stock 870 rifled slug gun is 3 moa (100 yards), due to the tolerances involved (barrel/action slop). That isn't bad, for woods hunting.
The soda can shim rivals pinning a barrel, is less costly, and may improve accuracy enough to meet your needs. It's certainly worth a try, since it is inexpensive and simple.
I haven't done it yet, but I plan to try it as a winter project. I also have another thing I want to try. I think that if you use a good release agent on the interior of an 870 action (ie multiple coats of wax), you could reduce the action/barrel slop by putting a thin, uniform coat of good epoxy/bedding compound (ie steel bed or marinetex) on the exterior of the barrel (where it would be in contact with the receiver). After the epoxy it applied to the barrel/chamber area, slip it into the receiver, and lightly tighten the barrel nut and let it cure for a few days. Once it sets, I believe that you should have a minimal tolerance ("tight") barrel/action interface, which is removable, and low cost, and leaves the action unmodified in case you want to clean it or use another barrel.
For some reason, pinning a barrel never intrigued me. You'd need at least three pins around the chamber area to lock it up (3 points determine a plane)-and keep the bore axis centered. Epoxy does this and more. The soda cam shim is the similar appoach, just completely reversible in minutes. There was a good comment on that thread the mentioned a benefit of using a longer shim, that would wrap around the barrel more than 180 degrees. This would go along with the theory of keeping the bore axis centered, and hopefully improving accuracy.
Good luck. Make sure you get several fired groups to make a "BEFORE" and "AFTER" comparison, to give a finite result to your accurizing project. Should be a fun thing to do.
