I recently purchased a M590 from a fellow officer. When I purchased he said it could not be loaded with more than five rounds without the follower binding on something. But the price was right so I figured what the hell. After I got home with it I tried to put six in the gun and sure enough the follower hung and I had to disassemble the gun to unload the mag tube and unbind the follower. Using a flashlight I found the problem. The mag tube has a very small dent that did not even scuff the finish on the tube. But, it is enough however to bind the follower and stop the gun from feeding. I called the guy up and asked him what he did to damage the tube like that. He said the gun started messing up on the range while practicing some room clearing. I figure that he swung into a door jam or corner. Here is the scarry part the damage to the tube is only visible in good light it is so minor. I tried to take a pic with my digital camera and could not get it to show upits so small. Anybody have any suggestions on a fix. Is replacing the mag tube a viable option for a doityourselfer. Anybody have a source for the tube other than Mossberg? I have a Email in to them about it but I have not heard anything back yet. What do ya think?

Get a large wooden dowl rod that fits in the tube just right and push it all the way down to push the dent out.  You may need to use a mallet but be carfull. this should nock it out for you.

A gunsmith that specializes in shotgun repair should have a hydraulic dent remover.  Used to fix dented barrels & mag tubes.  Brownells's sells the tool but it's kinda $$$$$ ($467!!!!!! ) for a one time DIY project.
Hydraulic dent raiser

They also offer a simpler mag tube dent raiser for much less $$$$ (still not cheap though, $75) half way down page

The mag tube shouldn't be too hard to replace, I've done it before on my M500 Mossberg.  Place receiver in padded vise, grip mag tube near base with strap wrench & twist.  

Numrich Arms/Gun Parts Corp has M590 mag tubes here but it doesn't say if it's the long version or the short.  $25

Havlin Sales & Service is another good place for Mossberg parts, probably better than GPC.  Havlin Sales

+1 on Numrich.  If you have questions on the size of the tube they are pretty good about answering questions.  But I do know that they list both a model 500 mag tube and a model 590 mag tube.  The 590 tub is the longer one.  They also showed Parkerized or Blue finish versions.

I beleive a Wilson or Vang Comp HI Viz follower is smaller diameter and would pass over the dent no problem.

I think I will try the Wilson follower. I was able to remove some of the dimple by using a small fine rattail file. The dimple is approx four inches from the muzzle end of the tube and I was able to file the worst of it off I think. The factory follower still will not function but I think it is getting there.

You could, in true WECSOG fashion, drill/Dremel the dimple out.......
It'd work but you'd end up with a "drain hole" or vent in the mag tube.