This is a three-part article to show how a Mossberg pump shotgun is disassembled and cleaned up. Not every shotgun will need to be taken this far apart. If you are not comfortable doing this sort of work, it is best left to an experienced armorer or gunsmith, but really, there is nothing hard about the work. The gun used for this article was a "bargain-rack" junker bought for not very much money because it was in neglected condition. The barrel was brown with surface rust and had pitting at the rollmarkings. The entire gun was covered with greyish crud and the action was so stiff it took both hands to work it. The fired hulls would not eject unless you turned the gun sideways with the ejection port down. Sometimes it double-fed when cocked. Sometimes it did not feed a shell at all. The safety was stuck in the "fire" position. But generally, when a shell was loaded, it locked up, fired, and worked OK, and I didn't see anything that was actually BROKEN, just a lot of dirt, dried grease, and neglect. I did not include pictures of the barrel refinish or cleanup of the stocks because I didn't think to take any until afterwards. I hope that anyone who reads this finds it useful. Howdy, I'm Mini-Evan. Today I will be your guide as we explore what's involved in tearing down and inspecting a Mossberg shotgun. If your eyes are sharp, you'll notice this specific shotgun is actually a Western Field. These were distributed by Montgomery Ward under that brand name. Like Sears, Monty Ward didn't actually make any of their specific branded products, and they were made by well-known makers. This shotgun is actually a Mossberg M550A, which is a 12-guage pump with a 5-shell magazine and wood furniture. The M500, 550, 590, and 600 should all be pretty much the same as this, and the Maverick 88 models will be similar, with a few minor changes such as the lack of a tang safety (the safety is included in the trigger group as a cross-bolt style in the Mav88) and the method of attaching the foregrip to the action bars. The first thing to do before starting any work is to visually and physically inspect to make sure the gun is unloaded. Check it twice. Open the action and stick your finger in the magazine tube and chamber to make sure no surprise shells are left in there. If you're small like me, you can just climb on in and get a really close look...leave the action open halfway for the next step. To start disassembly, this knurled knob needs to be unscrewed. It is what holds the barrel on. Sometimes they are very tight and padded-jaw pliers might be needed. As the knob turns, you will feel clicking or notchiness. This is a series of grooves machined into the surface to act to lock the knob from unscrewing. Once the knob is spinning freely you will see that it is retained in the barrel lug and as it loosens it draws the barrel forwards. Once it is all the way loose, you can pull the barrel out of the receiver. Make sure the bolt is not closed since a lock lug in the bolt engages the barrel. Also depending on the shape of the foregrip you might need to move the action in or out a little to get clearance to lift the barrel off of the magazine tube. Once the barrel is off, set it aside. This is the magazine tube. It screws into the receiver with a standard thread. It must be unscrewed to remove it. Often this is very tight or may have sealant on the threads. The best way to get it broken loose without damaging it is to use one of those rubber pads used for unscrewing tight jar lids. If that won't work, padded-jaw pliers on the very end of the tube where it is welded closed on the barrel nut might work. Don't try this in the middle of the tube or it might dent. As you unscrew the magazine tube, be aware the magazine spring and follower are under tension. Keep a good hold on the magazine tube to prevent parts from explosively disassembling themselves. The follower will often be left in the receiver, and the spring just pulls out. If your gun had a magazine restrictor plug, this would be how to get it out. The magazine tube and spring pull out of the foregrip and the spring just pulls out of the mag tube. The follower only goes one way, the cup shape goes over the spring. I like to paint the end of the follower a contrasting color (besides black) to be able to better see if there are shells in the magazine. Since 12-ga shells are usually red, I painted this one blue. The foregrip is retained on the action tube by this castellated nut. With the magazine tube removed you have more room to get to it. A pair of needle-nose pliers or a strong flat-blade screwdriver applied sideways (or, the correct style wrench if you have it) unscrews this nut. The foregrip nut is off! The wooden grip just slides carefully forward to remove it from the action slide tube. Sometimes lacquer or crud makes it stick on the tube, just jiggle and pull and it should come right off.