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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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.
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.
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.
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.
January 26, 2009, 11:00 PM
I'm loving it!!!!:D
Can you send me the parts in a box? I need to build something;)
January 26, 2009, 11:25 PM
Mini-me - good job. But, you better make sure all those little parts go back together just so, or else ya got problems.
January 27, 2009, 09:35 AM
January 27, 2009, 10:25 AM
HAHA! You sir, just made my day.
January 27, 2009, 01:04 PM
Love the instructions :D As I read them, I imagined a squeaky voice speaking the words :)
Excellent way of instruction.
February 25, 2009, 03:34 AM
BUMP, for someone having MOssberg problems...
March 14, 2009, 09:26 PM
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".
March 14, 2009, 10:48 PM
500C just means its a 20ga. 500A is a 12, 500D is a 410. The lesser seen is the 500B which is 16 gauge.
March 16, 2009, 02:34 AM
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?
March 16, 2009, 03:55 AM
I dont have to pull the trigger on my 590 to remove the group.
March 16, 2009, 08:05 AM
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.
March 16, 2009, 09:10 AM
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.
March 16, 2009, 11:58 AM
Pure Win !!!
Funny and Educational with Great Info.
Bravo and Well Done, Sir !!!
February 24, 2010, 08:20 AM
Must TTT this
Purely because it is so awesome.
April 29, 2010, 12:21 PM
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.
April 29, 2010, 12:26 PM
Quite brilliant...! :D
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... :)
April 29, 2010, 01:50 PM
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?
April 29, 2010, 08:51 PM
Great job I like it.:cool:
April 29, 2010, 11:14 PM
A picture is worth a 1000 words.
And a picture with Mini-Evan astride, in, or next to shotgun is worth 2000.
May 2, 2010, 02:13 AM
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?
May 28, 2010, 10:00 PM
This is one creative posting. Thanks very much. My girlfriend wants the name of the little guy with the muscles.
June 9, 2010, 01:40 PM
oh my god. awesome. lol thanks!
August 17, 2010, 08:37 PM
LOL! THAT'S THE GREATEST!!!! Hahahahaha
August 23, 2010, 01:40 PM
I have done some work to my mossberg 500.
I have the short action for-end tube.
I finally found a replacement for-end grip i was able to grind down enough to accept the for-end nut I bought from midway to fit a Houge over mold grip.
I had to remove a small spring on the action arms just under the tube.
It looks like it serves no purpose.
My question is will the shotgun be reliable with out this spring.
from what I see the action arms are pined to the for-end tube already and the spring just keeps the action arms pointed up during reassembly. I think I can manage to reassemble without the spring from now on.
August 29, 2010, 09:10 AM
If anyone is still reading this post I figured I'd ask: My 500 FTF the last shell 99% of the time !! I was thinking I need a new srping ?? What say ye ??Thanks:confused:
August 30, 2010, 11:34 AM
Springs are cheap. Scrub out the mag tube when you install the new one. Betcha the problem's gone.
October 11, 2010, 01:30 AM
Hey Mini-me do you think you could do one of these presentations for disassembling a Browning Auto five?
December 12, 2010, 01:33 PM
That made my day!!
January 7, 2011, 04:13 PM
I've just purchased a Mossberg 500 in .410 is there any way that I can modify it for a home defense setup because I would like to use slugs and buck shot (I have shoulder and neck trouble that prevents me from using a 12 or 20)
The factory barrel is 24 inches and it has a fixed full choke,also for some reason it is plugged to hold only 3 shells (two in the mag one in the chamber,the factory info says it should hold 5+1).
Any help would be appreciated.
January 7, 2011, 04:33 PM
You will have to remove the plug to be able to load it to full capacity.
They place plugs in them due to the migratory bird laws when your hunting such species.
As it come right out of the box it is capable of shooting slugs and buck shot.
Most 410's I have seen use full chokes because of their small shot payload compared to other gauges.
January 7, 2011, 04:51 PM
But wouldn't the full choke be a problem with accuracy if used with slugs?
It's a 500 E if that helps matters (I took it down and couldn't see any type of plug )
Also I'm using 3-inch shells (Birdshot for now)
While I have no doubts that it is a fine hunting gun,it is going to be used as a home defense firearm and at the most it will be used as a pest control tool (garden gun)
January 7, 2011, 05:53 PM
Pfletch,again most 410's use a full choke and since in my strongest opinion these gauges should never be used for deer hunting,I am not sure how much slug use you intend to use your 410 for but the truth be told just because it has a full choke does not mean it wont fire a slug somewhat accurately.
I doubt seriously the slugs will hurt it.
And the buck shot certainly will not hurt the barrel.
About the plug.
Did you take the magazine cap off and remove the innards to reveal the plug?
Unless the 410 is a completely different gun from other 500's,which I doubt, there is a plug in there to keep you from loading five rounds into the magazine instead of the factory plug induced two.
I have never pulled the plug from my old early 80's built Mossberg 500 but the one in my Maverick 88 is nothing more than a wood dowel.
Remington 870's use a plastic type of dowel.
Your owners manual surely shows you the disassembly procedure.
January 7, 2011, 06:16 PM
I took care of it
It's hard to get a hold of the little sucker (let alone see it) I had to load a few dummy rounds in the mag before I could get my hands on it.
January 7, 2011, 06:30 PM
Now all I need is an 18.5 inch barrel,a few boxes of slugs,a few boxes of buckshot and I'm set.
January 11, 2011, 02:04 AM
That was outstanding. I just ordered a manual so I could take my Mossberg down for a thorough cleaning and polishing and it isn't anywhere near as entertaining or easy to understand as this is. :what:
January 13, 2011, 06:05 PM
Thanks for the write up, I read through my manual but this was what I used to break my 500 down the first time.
January 14, 2011, 11:50 AM
Excellent piece!! Although I'd consider laying off the cartoons for a while.:D
February 22, 2011, 03:03 PM
I just signed up and this is the first post I read. Hilarious! Thanks for that.
March 2, 2011, 10:52 PM
haha! you sir have made my day! thanks for posting such a funny and useful thread!
June 3, 2011, 02:36 PM
Evan, You are very talented, this shows a lot of thought went into it. Very entertaining. It made me think of those comic book/maint. manuals they sent out with
M16s. Made my day.
June 13, 2011, 02:28 AM
Funny you should mention solvents on the trigger group as I once turned mine to goo in some nasty solvent. My fault!
June 30, 2011, 02:44 AM
I forgot to take note of which way the safety hook goes.
Which way does it go?
June 30, 2011, 03:12 AM
Nevermind, figured it out.. only goes one way.. the open side of the hook goes towards the barrel. A little good ole trial and error human learning.
June 30, 2011, 05:37 AM
Now just having trouble re-assembling it.
July 1, 2011, 07:30 AM
Ok, all done. Thanks to the OP for a good and illustrative guide.
Between disassembling my Mossberg 500 and painting it, and converting a SAIGA 7.62... I'm feeling like a regular saturday gunsmith..lol!
July 27, 2011, 07:40 PM
Awesome. just awesome.
July 28, 2011, 09:55 PM
Great job for mossy 500 owners.
July 28, 2011, 10:06 PM
LMAO!!!! 5 STAR POST!!! In all this time, I had never seen this post! :D:D:D:D Excellent sir!
August 4, 2011, 12:09 AM
Shame, shame. Mini-Evan had his leg in the trigger guard before he was ready to shoot.
Excellent guide, by the way.
August 31, 2011, 07:37 PM
haha Interesting way to learn; however I have had A mossy 500 for several years and I have never had to take it down that far...
August 31, 2011, 08:44 PM
Hey Evan, super cool/informative post.
September 5, 2011, 01:23 PM
How about having the little guy take a shot at a Rem 870. From what I can tell it looks like most of the Moss 500 will apply, but have never actually taken one apart. Just got a pawnshop 870 and need to repaint the receiver and barrel [flat black] to deal with some surface rust. The whole gun is black so the match won't be an issue, just think it best to disassemble the gun to avoid getting overspray on the trigger group or whatever. Anybody have any suggestions or advice on the paint touch-up?
September 25, 2011, 01:07 PM
I have not visited this board in a while. As an Armorer, this thread tickled me to death. Very cute and informative. TOGGLELOCK
January 11, 2012, 06:32 PM
Great post, thank you.
April 29, 2012, 04:04 PM
Hilarious, good job .
July 26, 2012, 01:26 PM
A little cheesy, but accurate. Nice job.
I just picked up a Western Auto Revelation 310A (modifying for tactical/home defense) and it is virtually identical. I will document the differences as I determine them.
I had to repair a broken safety and found that the 310A's Safety Block uses a different hold down screw and shorter detent spring. So far most parts interchangeable.
August 26, 2012, 09:08 PM
HOLY, HOLY CRAPOLA.....this was, in fact, the most enjoyable "firearm" thread I have ever read. Funny, funny, funny, and smart!
September 3, 2012, 09:26 AM
Picked up a Mossy 500 at the Indy 1500 last weekend. Looking forward to stripping it and cleaning it now! Great post. Very creative.
March 24, 2013, 07:31 PM
I'm sure I will use this when the MBerg 590 comes home...;)
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