View Full Version : Barrel Wobble in Mossberg 500, Need Advice

November 19, 2008, 05:51 PM
I have a Mossberg 500 with a field barrel and a rifled barrel. When I switched from the rifled barrel to the field barrel, I noticed that there is a very small amount of play between the barrel and the receiver. I have followed all of the directions in the manual, which does not even address this issue. I have fired many rounds through the shotgun in this condition. The same play is present in the rifled barrel, which has a cantilever scope mount. I read that the reason that the cantilever mount is included because if the scope wobbles with the barrel, eliminating the inconsistencies present with a receiver mounted scope. I am very happy with my Mossberg 500, and when I switched from the rifled barrel to the field barrel and back, the scope still held zero, which I thought was pretty amazing. Very nice deer gun and dove gun and general all-purpose firearm. I basically only notice the wobble while I'm holding the barrel in one hand, the stock in the other, and gently wiggle the parts.

Is this very slight wobble in the barrel safe and/or normal? Is it something I need to address? Is there a good way to eliminate it? Am I just worrying too much?

November 19, 2008, 10:17 PM
Hey Buckhammer. I've got the same setup and let me see if this helps. I've had problems seating both barrels after swapping. The manual talks about opening the bolt 1/2 way, but mine sure is finnicky about that. It might be more like 5/8 or so. The way I know for certain is the gap between the mount for the barrel nut (if that's what you want to call it, I don't know the official name. Its the piece the bolt is attached to that screws into the end of your magazine tube). If the barrel is fully seated, there is no gap. If there is any gap, the barrel has not fully seated in the receiver.

Once mine is screwed on tight, it doesn't wobble.

Let me know if that helps. If not, I'll go look at it tomorrow and see if I can figure something else out.

November 21, 2008, 07:29 PM
Tried everything. Did what the manual said, which was while seating the barrel into the receiver to gently rotate it back and forth. I tried to put it in with the bolt more/less open. I tried everything except tightening the screw with a wrench (which the manual said NOT to do). Still a little bit of wobble. The rifled barrel is still accurate and it seems safe, so overall, I'm not terribly worried about it. Thanks for the advice anyway. There really isn't much wobble at all, but there is a wobble present. My main concern was, and is, safety. I would, however, feel more comfortable with NO wobble, so if someone has a sure-fire way to fix this issue, please let me know.

November 22, 2008, 12:31 PM
I would not recommend that you attempt to tighten the barrel attachment nut to the point of barrel lug pinch against the end of the magazine tube.
Any such advice is faulty and can mean that force is being used to tighten a nut made to be finger-snugged only (pliers are right out) or else you have one of very few examples that don't have the best fit of parts from the factory. If the tube was a bit long or not fully seated into the frame, it would extend slightly more and take up the 1/32" or so gap normally seen when the barrel is fully seated and the nut snugged.

Get the owner's manual here:


Look at page 6 to see this:
Slide the barrel into the receiver and tighten the takedown screw, finger
tight only. DO NOT use pliers or a wrench to tighten the takedown screw.
A little space between the magazine tube and the takedown mount is

The wobble is something that may be reduced or eliminated by other means, such as a refit of certain parts to decrease the clearance to the point of a jam-fit, but then you don't have rapid barrel swap, do you?

One process to make parts interchange but mount securely is done with lug-nuts torqued to 80 foot-pounds; in other words, special design parameters that cost time and precision machining are not going to be incorporated in an economy design (and sometimes not in expensive designs, either).

A simple improvement would be to install a washer shim between the mount and tube end that was no thicker than the gap when measured with feeler blades, or maybe .002" thinner, at most, and only for use with that specific barrel or others that measured the same gap. That would allow a "pinch" at that end to eliminate a portion of the built-in slack, and any barrel swap would not be compromised in speed.

Any excess tightening of the barrel attachment nut to draw in a gap will cause a bend in the barrel/lug joint along the barrel underside and make a deformity that I have been able to see inside the bore.

I advise you to take this advice.

[email protected]

November 22, 2008, 12:37 PM
Even if you use channel lock pliers you will still have a gap 'tween the lug and mag tube... If you overtighten it you will break the barrel or damage the tube or both.
What I do suggest in your case is to mic the reciever and barrel. Also look for a fracture of the receiver. USE A BRIGHT LIGHT... I have no noticeable wobble once my barrel screw is hand tightened.

November 22, 2008, 10:55 PM
Get the owner's manual
I'm not trying to be rude, and with all due respect, I originally hoped that this part of my original post:
I have followed all of the directions in the manual
would relay the fact that I had a manual (which came with the gun), had read it, and had followed the directions that it contains. I did not and will not use a wrench or pliers. I am worried that that came off as rude, which is certainly not my intention. I do appreciate the response.

So, would I be correct in saying that the wobble is something I'm just going to have to live with, unless I undergo expensive and taxing work on the weapon? As I said, the function is flawless and reliable, and it shoots straight. As long is there is no safety concern, then I can live with a slight wobble. I'll make sure to check for a fracture, although that does not appear to be the case (I could be wrong, I am not a gunsmith).

Thanks for the input, I'll look into employing one or more of these ideas.

Katrina Guy
November 23, 2008, 09:52 AM
...getting a Mossberg 500 field shotgun and a secondary HD Barrel, I'll stick to plan "A" which is to buy a Mossberg Persuader.
It pays to come in here and read threads!

November 24, 2008, 12:19 AM
Once upon a time, I used to note with my postings that the information that I might impart would be of help if it included more than just the basic or minimal information needed by the original post or subsequent queries and answers.

The world of internet forums is not a vacuum with only person A and B in the conversation, so any spare or possibly redundant or seemingly filler info. is for the benefit of future readers that may not have the benefit of having the owner's manual, for one particular instance here, for example. That's why I posted "get the owner's manual here", not "get the owner's manual".

It never pays to take an incomplete thought out of context.

That is why I also included the paragraph from the available manual- to save time for some readers to note where I was referring.

I was definitely going to make a note that the globemaster was offering information that would be incorrect in almost every instance and referenced the factory info. as added ammo. I also noted why it might have been that way for his specific example beyond the point of sloppy factory tolerances of length match-up, so that readers would not then consider that I was slapping him about.

The possibility of frame cracking is much less than dirt or burrs at the barrel breech end and seating surface inside the frame inhibiting solid contact. More than one part has come from the factory with a fresh floor bounce ding or 2.

The variable fit and snug nature of different frame/barrel combinations can be improved with only moderate expense and still be to the point of decent R & R & R, but for me to do work to minimize slack in parts would require having the parts and barrels here for reworking and precision fitting.

Now you must decide- curious or serious.

Mossberg and other action reworking is one specialty of mine.
See my other posts for more input from a gunsmith's perspective.


November 24, 2008, 07:13 AM
globemaster was offering information that would be incorrect in almost every instance

Kirby, thanks for the slap. As an owner/operator of this firearm, I know how it operates, have read the manual, and did not/would not suggest someone to do something against either, since that would be unwise/dangerous.

Notice I did NOT suggest to him to use anything (read tool) to tighten up the bolt used to attach the barrel to the end of the mag tube. One thing with this combination is the barrel will seat partially, but not all the way, with the bolt assembly not in the correct position. In this case, you could partially screw your barrel bolt into the mag tube, but it would not be fully seated as indicated by an expansive gap between the two parts as described, wobble incredibly, and be dangerous to shoot. I find with MY particular gun that it needs to be open a little more than the factory recommends. Is that suggesting something dangerous? Are you kidding?

It sounds like the OP is still experiencing some wobble with it fully seated. As offered, once I clear the plate a little, I'm going to go look at mine, as offered, and see if I am missing something.

November 24, 2008, 07:55 AM
it may have already been posted,but make sure the magazine tube is tight. eastbank.

November 24, 2008, 12:51 PM
If what I mentioned wasn't easily noticed, I will repost here.

I would not recommend that you attempt to tighten the barrel attachment nut to the point of barrel lug pinch against the end of the magazine tube.
Any such advice is faulty and can mean that force is being used to tighten a nut made to be finger-snugged only (pliers are right out) or else you have one of very few examples that don't have the best fit of parts from the factory. If the tube was a bit long or not fully seated into the frame, it would extend slightly more and take up the 1/32" or so gap normally seen when the barrel is fully seated and the nut snugged.

This is what I was referencing from globemaster:
If the barrel is fully seated, there is no gap. If there is any gap, the barrel has not fully seated in the receiver.

Once mine is screwed on tight, it doesn't wobble.

The point was also referenced to the owner's manual statement about the gap.
If you had read my posting thoroughly, I believe it would be noticeable that I wasn't saying all of what the globemaster posted was bound to be incorrect (in almost every case) since what I referenced was in my opening sentence and the following comments addressed the specifics of that point, as well. You will find no reference to anything about how far a bolt must be open, etc.

Since you (globemaster) say your gun will allow the barrel to barely enter and feel snug just from the first bit of barrel takedown screw thread engagement, perhaps it is now prudent to mention this particular warning from the owner's manual referenced:

(all models): Check to be certain that the barrel is fully seated into the
receiver by looking through the ejection port. The barrel extension must rest firmly
against the corresponding cut in the top of the receiver as shown in Figure 4.

I am certain that would be of benefit to readers beyond the specifics of a particular finicky gun. Your situation is anecdotal but can certainly be of interest. It just doesn't happen to fit the predominant expected condition.

You must decide whether I would be better to leave incorrect information without correction, include additional details for beneficial analysis, make note of available manuals for other readers, or take offense when none was intended. I am not offended by any particular mistaken impression- just by specific accusation. Even then, I will attempt to assuage any mistaken hard feelings and will also point out my own mistaken impressions or incorrect information, wherever found.

The note about checking magazine tube tightness should be useful, since it is something easily checked by hand, but not always recognized when first starting to loosen.


November 24, 2008, 05:06 PM
OK, lets clear a few things.

I checked mine, got out my owners manual, and sat down and swapped barrels on both my 12 ga and the daughter's 20 a couple times to refresh my memory. I might have given a false perception before that the gap was between the block and the mag tube. That would be false.

The gap I was thinking about was between what the manual calls the "takedown screw" and the "takedown mount". In both cases, when the gap was taken out, the "barrel extension" was fully engaged with the "ejector tang." Now, when fully loosened so the "magazine takedown screw" is fully disengaged from the magazine tube, on both guns you can see a gap between the screw and the "takedown mount" to the point where the ball that acts as a detent that engages in the mount is visible on the aft surface of the screw. This is the gap I remembered/was trying to explain in my ramblings.

As far as the open "bolt", what I was trying to explain was the bolt in the chamber. The directions specify to open the chamber 1/2 way. (Listed as step 2 on my barrel manual" Depress the action lock lever and move the forearm rearward until the front of the bolt is in the middle of the ejection port." Instead of 1/2 way, my particular 12 ga likes it a hair more, about 5/8 way. As long as the barrel extension seats in the tang and the magazine takedown screw is tightened finger tight, that is the objective.

I did check the "wobble" in both. On the 12 ga, with the "takedown screw" fully seated (always finger tight), I had an almost imperceptable amount of play by attempting to rotate the barrel clockwise/counterclockwise in relation to the longitudinal axis of the gun (possibly 1/32 inch?). On the 20 ga, there was absolutely no play whatsoever (yes, the "magazine takedown screw" was only finger tight.)

So, to the OP, you can use this as a benchmark to gauge your wobble. I've owned the 12 ga for only 20 years or so, the 20 for about a year.

Perhaps the mistake was mine in my inferior references. I see what I meant in rereading my post, but see how if you were not in my head I was not clear. Hopefully, now that I have had time to reference the book on this, go out and handle both my weapons, I've been able to provide more measureably accurate data for which to make an opinion on the severity of your "wobble".

November 24, 2008, 05:50 PM
Sorry, Kirby, didn't mean to take anything out of context. I was really not trying to attack you. I was just saying that I own the manual, the hard copy, which came with the weapon, and had it in front of me, so I didn't really need an online one. I also noted that I had read it and followed the directions contained in it. Then again, on second thought, that information could be helpful for those with a similar problem but do not have the manual. Again, I apologize if you feel attacked or exploited or taken out of context in anyway, that was really not my intent. My intent was that information from the manual didn't help and I needed advice besides what's contained in the manual.

I fully apologize for any offense my previous post may have caused, you are trying to help me, and I fully thank you and appreciate the advice.

EDIT: Also, my wobble is almost imperceptible, so I guess its no big deal?

November 24, 2008, 06:29 PM
Buck, I bet Kirby has thick skin too and likewise wasn't intending any offendin'... This innernet thing is easy to misunderstand...
Also I don't think you have an issue with your gun... If it jangled when you jiggled it... I would send 'er in...:D You'll find I am not aware of a "fine shotgun" since these mossbergs are great for me. When I walk in the woods I always have it in to hands. The forestock in a twist to keep it and the action bars quiet:rolleyes:....

November 24, 2008, 06:48 PM
Buck, I'm thinking you are OK with that. Mine has shot slugs well using the 400gr winchester platinum 2-3/4", FWIW. The last shot I took with it was a 130# boar at 75 yds. Got the heart, both lungs, and recovered the slug right under the skin on the opposite side. He took 5 steps, found out he was already dead, and dropped right there.

I guess that's my long winded way of saying I've not experienced any problems with the wobble.

November 24, 2008, 08:43 PM
Alright, I'll stop worrying. Thanks, guys.

Ricky B
November 25, 2008, 01:07 AM
I was going to suggest that the OP take the gun to a gunsmith to have it looked at, but I guess that's too obvious a suggestion. My Mossberg 500 barrel doesn't wobble, but if it did, I would take it to a gunsmith.

November 25, 2008, 03:19 AM
i got my mossy 500 when i was 12. it had "barrel slop" for almost 10yrs, till i fell and dented the mag tube.
now there is no slop. go figgure.

March 27, 2009, 01:29 AM
Alright, I'll stop worrying. Thanks, guys.
Well, I was unable to stop worrying. After being frustrated and upset often by seeing my friends' Mossbergs without any barrel wobble, I finally just decided to disassemble it entirely and go from there. Upon disassembly, I discovered that the magazine tube was slightly loose. This is what was causing the barrel wobble. When I reassembled the shotgun, I made sure that the magazine tube was tightened properly. It now has no barrel wobble at all. I could not tell that the magazine tube was loose without disassembling it.

I realize that this thread of mine is old and I'm resurrecting it, but I only just now fixed the problem and I thought that it may help others in a similar situation.

Thanks everyone for your advice and assistance while I was having this problem, I greatly appreciate it. I feel like an idiot for not realizing what the problem was sooner, and lazy for not disassembling it earlier. I hope my experience will help someone else who may be having this problem.

Ricky B
March 27, 2009, 11:31 PM
Good for you for figuring out the problem, and I'm glad you came back to give us this report.

March 28, 2009, 12:51 AM
Hopefully I can add my .02 into this thread and warn people to take a good look at what the barrel looks like seated before they disassemble it to properly eyeball-gauge it when they go to put it back on for the first time. Don't let the heatshield gap fool you as it did me on the 590 when I didn't know what I was doing either...best to open the chamber and see if the tabs are threaded in there. Can be kind of confusing but the best place to look is the side of the barrel and inside the receiver where the barrel tabs meet the grooves.

April 7, 2009, 07:26 PM
to fix a mossberg you:

1. say a bunch of nasty words really loud.
2. swing that mother as hard as you can against the biggest tree in your yard.
3. put the gun away as it is either fixed, or worth the same amount as before you beat it on your tree.
4. drink more beer