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Old January 26, 2009, 10:12 PM   #1
evan price
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Mossberg 500 Shotgun Disassembly Guide by Mini-Me

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.
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Old January 26, 2009, 10:13 PM   #2
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>Part II of Mossberg Disassembly Guide<





The round thing in the receiver I'm pointing at is the trigger group retaining pin. It goes all the way through the receiver (and can be seen on either side) and keeps the entire trigger group in place.





To remove the trigger group requires a pin punch. I find that the easiest thing to use if you don't have one handy is a common nail. If you're worried about scratching the end of the pin, file down the sharp tip. My experience is to go left-to-right and push the pin all the way out of the receiver.





Here's the receiver pin, removed. There is a spring retainer in the trigger group that engages the groove on the end of the pin to keep it locked in there. Just pushing out the pin releases it, there's no funny business here.





The trigger group tilts slightly up at the back, then slides a little towards the butt to disengage the front lip from the receiver. Then it just lifts out. Don't worry, it's all one captive unit and it won't kersplode when you take it out.





This is the trigger group, removed. It's all one unit and it is not necessary to take it apart unless something is really wrong with it. If it needs to be cleaned, be aware that the main body is made of plastic, and any solvents or cleaners used need to be safe with plastic. An aggressive solvent may turn the plastic white. It might also turn it to goo. Generally a good brushing out and some gun oil on the moving parts is all this needs.





Inside the receiver, a couple of parts may have fallen out when the trigger group was removed. The slots in the receiver they ride in need to be cleaned of old grease and dirt.





The small bar of metal on the side of the receiver is the shell stop. It keeps shells in the magazine tube.





This is the interruptor, it is the piece that goes on the ejection port side. It has a pivot that fits into a hole in the receiver. Its job is to prevent shells from double-feeding from the magazine tube.





With the shell stop and interruptor out of the way, we can see this piece of metal. It is called the bolt slide. It is what links the bolt to the action bars and cams the bolt up to lock into the barrel when cocked. It can be lifted up, disengaged from the action bars, and removed. Make a note of how it goes in.





With the bolt slide removed, you can now remove the action bars and slide. My friend here helps me with the heavy lifting and he wanted to be in a picture, too. The action slide & bars just pull straight out of the receiver. Check the bars' attachment to the slide for rust or looseness, I have seen the welds break once in a while. Also clean the slots in the receiver where the bars ride because these are dirt traps.
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Old January 26, 2009, 10:14 PM   #3
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>Mossberg Disassembly Guide Pt. III<





This is the shell lifter. It is what drops down to pick up the shell coming out of the magazine, then lifts it up to the bolt. It should be fairly loose now.





The shell lifter has two pivots, one on each side of the receiver, where I am pointing at.





To remove the shell lifter, raise it up and squeeze it together until you can get the pivot pins out of the holes in the receiver. Then just lift it out.





Once the shell lifter is out, the bolt assembly just pulls straight out of the receiver. You can see the two spring-loaded extractors (held in place by pins). Clean these so that they move freely. If they get crud trapped between the extractor and the bolt body, the extractor may slip on the shell rim and you get jams.
You can also see the firing pin. It should be clean and move freely in the bolt. The bolt ramps are what locks in to the bolt slide and cams the bolt up to lockup with the barrel when the action is cocked. It should also be clean. A little gun oil here will work wonders on how the action feels.





This is the tang safety. The Maverick 88 won't have this. This safety is held on by the small flat-blade screw in the center. There is a small steel ball pressed into the receiver under the safety knob. It shouldn't come out, but it might. Before you remove the screw, look inside the receiver and see how the metal safety hook is pointing. I like to touch up the red paint in the safety "Fire" position.





When the screw is unscrewed, the safety hook falls out.





Here are the pieces of the safety: there is the plastic knob, there is a metal spring plate that is under the plastic knob (has holes in it), there is the screw, and there is the safety hook.





This screw holds in a small metal piece which is the ejector. It is what pops the spent shell sideways out the ejection port. Remove the screw and the ejector should just lift right out of the slot it fits into. Take a look at this and make sure it isn't bent, that the slot isn't full of crud, and that the hook on the end isn't worn out. With the bolt removed, the ejector should be sitting with the end furthest from the barrel up higher than the slot. The ejector pushes down when the bolt moves past it, then springs back up to catch the rim of the shell and flip it out the ejection port.





Here's the ejector. Check it over for cracks or wear. It should be fairly stiff but springy. Often a weak or worn ejector will cause jams as the spent hull does not leave the chamber. New ones are not expensive, and bending a worn ejector will only work for so long.





To remove the buttstock, first you have to take off the recoil pad. This is usually held on by a couple of Phillips screws. Just stick a screwdriver in the holes in the pad and feel for the heads of the screws and unscrew them. You can see the screws in this picture.





The buttstock is held to the receiver by a longish, largish screw. Some of them are Allen headed, most are straight-blade screwdriver slotted. You need an extra-long 1/4" blade screwdriver to reach to the bottom of the buttstock to remove the screw. Then, the buttstock just pulls off the receiver.


The receiver should be checked for damage, cracks, and wear. Ovaled shell-lifter pivot holes are possible. While the receiver is not stressed to chamber pressure in the Mossberg design, it is still possible to be damaged by mishandling or abuse. All the slots and grooves in the receiver should be cleaned and lubricated with gun oil. All the pieces of the gun should be cleaned and checked for damage or wear before reassembling. I have seen where action bars have had the spotwelds that hold them to the action slide break loose, usually from somebody trying to "Hollywood" the action (one-handed cocking by flinging the gun up and down) or on heavily used & poorly maintained guns. It's normal for some side to side slop on the action slide as it sits on the magazine tube, and some twisting looseness is normal.

Re-assembly is the reverse of dis-assembly. Use caution and function test the gun after putting it back together before you put it back into service. I use a couple trimmed, empty shells to test for feeding and function before using live ammo. Above all, check the function of the safety and trigger parts to not fire if bumped, slammed, or banged.

The Mossberg pump is a simple, durable gun, and if maintained properly, will provide years of service.

Happy shooting.
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Old January 26, 2009, 11:00 PM   #4
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I'm loving it!!!!

Can you send me the parts in a box? I need to build something
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Old January 26, 2009, 11:25 PM   #5
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Mini-me - good job. But, you better make sure all those little parts go back together just so, or else ya got problems.
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Old January 27, 2009, 09:35 AM   #6
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Very nice.
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Old January 27, 2009, 10:25 AM   #7
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HAHA! You sir, just made my day.
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Old January 27, 2009, 01:04 PM   #8
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Love the instructions As I read them, I imagined a squeaky voice speaking the words

Excellent way of instruction.
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Old February 25, 2009, 03:34 AM   #9
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BUMP, for someone having MOssberg problems...
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Old March 14, 2009, 09:26 PM   #10
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Hi Mini-Evan,

I can't get the trigger group out!
Or the magazine tube!

Can I, in theory, do the rest of the disassembly with the magazine tube in?

I've drifted out the trigger group pin, but the assembly won't move. I can actually push it *into* the receiver at the rear, maybe 1/16" when the pin is out. Then I can use my brass punch to lever it back down into place thru the retaining pin hole. It feels really tight. I can't get it to budge at all in the coming-out direction. :-(
Do you have any suggestions?
I have a 500c. I'm guessing 'c' means "with stupid one-way screws on the safety and ejector".

Thanks,

-Daizee
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Old March 14, 2009, 10:48 PM   #11
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500C just means its a 20ga. 500A is a 12, 500D is a 410. The lesser seen is the 500B which is 16 gauge.
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Old March 16, 2009, 02:34 AM   #12
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OK, the mag tube will unscrew, but you might need to use a rubber jar-opener thingy to get traction, or else wrap the end of the tube (where the barrel nut goes in, there's a groove crimped in) with tape, and carefully use channel-lock pliers to break it loose- sometimes Mossberg put sealer on the threads.

The trigger group- hmm. Might try taking off the butt, sometimes it overlaps the receiver just enough that it jams the plastic in there. Also, the trigger is pulled, right?
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Old March 16, 2009, 03:55 AM   #13
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I dont have to pull the trigger on my 590 to remove the group.
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Old March 16, 2009, 08:05 AM   #14
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If it's a pistol grip stock or pistol grip only, it's almost guaranteed to completely block the rear of the trigger guard housing.

And I never pull my trigger during disassembly, either.

The magazine tube is generally supposed to be left in, which is why it's in so tight. For someone that really needs it off, I'd try a rubber strap wrench near the base, before trying channel lock pliers.
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Old March 16, 2009, 09:10 AM   #15
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The OP said to use the a rubber strap jar opener/oil filter wrench in the first post. You may need to take the magazine tube off to change the stock mag spring to a newer one.
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Old March 16, 2009, 11:58 AM   #16
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Pure Win !!!

Funny and Educational with Great Info.

Bravo and Well Done, Sir !!!
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Old February 24, 2010, 08:20 AM   #17
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Must TTT this

Purely because it is so awesome.
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Old April 29, 2010, 12:21 PM   #18
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Bolt slide

This is a very useful article. The only issue I had Is with the bolt slide. I had to play with it a bit to get it into place. But other than that, no problems. I have a mossberg 500 full tactical shotgun and this covers it all. If you have a colapsable stock or pistol grip this must first be removed in order to get the trigger unit out.
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Old April 29, 2010, 12:26 PM   #19
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Quite brilliant...!

I believe Mini-Evan needs to be put to serious overwork, performing the same instructions for a whole slew of shotguns, rifles, pistols, and revolvers...

.
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Old April 29, 2010, 01:50 PM   #20
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Very nice!

A couple of points:

Removing the mag tube is only needed if there is some work required on the mag tube itself. It will require a strap wrench. Do not use pliers! Normal cleaning and servicing does NOT require removing the mag tube.

Be sure to open the bolt BEFORE you try to remove the barrel.

So where's the reassembly guide?
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Old April 29, 2010, 08:51 PM   #21
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Great job I like it.
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Old April 29, 2010, 11:14 PM   #22
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Very creative.
A picture is worth a 1000 words.
And a picture with Mini-Evan astride, in, or next to shotgun is worth 2000.
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Old May 2, 2010, 02:13 AM   #23
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Brilliant! Nothing short of pure pleasure and one of the most clever ways to convey info!

I noticed Westerfield on the underside in one of the pics. I have a spitting image of this SG. Does yours have the C-Lect choke?

Will this SG accept slugs?
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Old May 28, 2010, 10:00 PM   #24
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Mr Price,
This is one creative posting. Thanks very much. My girlfriend wants the name of the little guy with the muscles.
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Old June 9, 2010, 01:40 PM   #25
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oh my god. awesome. lol thanks!
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