New Life for an Old Model 500!

I had two Mossberg 500 barrels that I wasn’t using on my main hunting shotgun, and that spelled “PROJECT”! One was an 18 inch cylinder bore riot barrel with no vent rib and a tritium front bead. The other was a parkerized 20 inch vent rib barrel threaded for choke tubes. At one time I had owned three Model 500’s, but was down to one.

I looked in pawnshops for about six months until I found the gun in the topmost pix of this page. It was a neglected mutt, and used plus abused! It had started life as a black stocked, mil-spec M500 with2 3/4 inch chamber and a riot barrel like the spare 18 inch one I had. The original barrel was MIA and the added barrel was 28 inches with a 3 inch chamber. It would fi re a 3 inch shell, but not eject the spent hull as the port was made for 2 3/4 inch shells only. Then there were several layers of spray paint camo applied over the matte black fi nish on the aluminum receiver and synthetic stock set...

In this picture, look at all the rust and corrosion on the internal surfaces of the receiver and on the mag follower, but the price was right at $100. I knew from past work on these guns that if the follower was that bad, the spring would be worse. Adding to the diffi culty, MOST Model 500 mag tubes are red-Loctited in place. You have to heat the steel mag tube up just enough to make the loctite begin to smoke, but in a careful, gradual manner that won’t warp the aluminum receiver.

Since the barrel headspace is set at the factory by the distance of the muzzle end of the mag tube to the front face of the receiver, it’s pretty important to get the mag tube BACK to that position at reassembly. So I counted (and made a note) of 2 exposed threads not set into the receiver, then used a small sharp chisel to leave a witness mark on both receiver and mag tube to assure proper indexing of the tube.

For safety, I prepped my work area carefully before fi ring up the propane torch. A fi re extinguisher is right off camera, and note several layers of heavy-duty foil protecting the table. Also notice that I have a fairly clean work area and no paper nearby. Gloves and a BBQ lighter fi nished the prep work.

In the picture below, I have clamped the receiver as tightly as I felt I could without crushing it between the two wood blocks. That blue clamp is a BEAST that weighs about 12 pounds!

This set-up would insure the best chance of breaking the tube free once the right amount of heat was applied.

Once I fi red up the torch, I never let the fl ame get any closer than 3/4 of an inch from the receiver or let it stop in one spot for more than 5 seconds at a time. I worked back and forth around the tube from about 3-4 inches from the receiver to back within that 3/4 inch. It took about 5 minutes of this for the fi rst smoke to rise from the Loctite.

I shut down the torch, and grabbed my pre-positioned strap wrench. Note that I put the rubber strap no closer than shown to the heated area. I had done a dry-run of this part before I started with the torch so I knew that I would still have a ton of mechanical advantage from this position to bust that sucker loose.

It came loose with only about two-thirds of my strength brought to bear, and I rotated it around two full turns before I took the wrench off to turn by hand.

Notice I still have heavy gloves on. That tube is hotter than it looks!

Carefully fi nish turning the tube out. Be aware - there’s a big captured spring in there! Keep control of the tube and ease the pressure off slowly as the tube comes off.

Make a note of this, I would only apply blue, removable Loctite upon reassembly. Since the factory worries about improper headspace if you don’t take caution, they use the permanent threadlocker to lessen the chance of liability if reassembly is done wrong.

YUCK! In this case, I hate being right!

Since the mag spring is not easily serviceable, most I have encountered have been pretty well abused.

This one is as bad as they come though...

I straightened the kinks as best I could, then counted coils instead of measuring length. That will always be more accurate after the factory spring has been under compression for several years. I also add at least 2-3 coils at fi rst and leave them if the weapon functions with a full load of shells. If it won’t accept the specifi ed amount of shells, then I remove and clip back a couple until it will.

Note the kinks in the spring that are even more worrisome than the rusting. I might HUNT with that spring, but not bet my life on it!

The new spring comes from Wolff Gunsprings(www.gunsprings.com) and I also went with a high-visibility synthetic follower. This model from Choate (www.rifl estock.com) is as rugged as it is functional, and it will never rust like the factory one.

Wolff replacement springs are made to trim to fi t. Clip the spring neatly with a quality wire cutter, then remove the burr at the cut end with some fi ne sandpaper.

I use a pair of non-marring (without grooves) pliers to bend the spring to have a fl at coil at each end. This will also help eliminate kinks.

It is easy to see how the fl at end would produce a more even pressure on the follower.

I chucked an old section of synthetic ramrod into a hand drill and put some 000 steel wool into a slotted shotgun rod tip. I plugged the muzzle end of the mag tube and squirted in a healthy dose of light oil. Then I put on goggles and a shop apron and went outside before polishing the heck out of the inside of the mag tube.

Replace the wad of wool as needed.

Keep this up until a patch comes out clean.

That will be a while!

There are a world of gun assembly books with info on the disassembly/reassembly of this fi rearm. But DO use one, as there are a few tricks that will save a lot of frustration.

After I fi nished polishing the mag tube, I stripped off the layers of spray paint from the tube and receiver. The original matte black fi nish on the receiver was still under the paint. I used a matching bake-on fi nish on the magtube exterior. Quite a difference from the gun I brought home from the pawnshop!

I used it two months later to harvest this Tennessee Tom during spring turkey season. Satisfying on many levels, I assure you...

When I change to the riot barrel, it makes a dandy home defense weapon as well!

- perklo

Notes on the Model 500 mag tube and model variants:

1) Because of the design, there aren’t aftermarket mag tube extensions for the Model 500. The military “Combat” version, the Model 590, has a longer mag tube and thereby a different location for the barrellug that screws into the mag tube. It also has a bayonet lug and heat shield.

2) A sub-model (Model 500A) was produced for a few years with a few mechanical differences. Most notable was a safety on the triggerguard instead of under the thumb on top of the receiver.