Upgrading the military shotgun – part 2 – the barrel and history of use


Part 1 HERE.
Part 3 HERE.

There is at least 35,000 Mossberg shotguns in use by our military. Means there are at least 5 or 6 of these guns for every M1014 in use. So there are plenty of them stack away in various armories.

In the civilian world, the shotgun is seen as a very versatile tool. From hunting small game, big game, or self defense, we have a wide variety of options in ammo and configurations. The military not concerned about the hunting side of things. The shotgun was generally used for riot control, security forces, and breaching.

I’m told the Army has more Mossberg 500s for each Infantry Brigade than M240B machine guns.

Riot Control
Security Forces

Using the Marine Corps as an example, in the past they used The Remington Model 11, Winchester Model 1897, Remington Model 10, Winchester Model 1912, and Ithaca 37 shotguns in the past. Eventually the Mossberg was adopted to replace all previous pump action shotguns.

It is often said that the Mossberg M590A1 is the only shotgun to pass the military torture test. This leads people to believe that the M590A1 model is the only one used by the miltary. Fact of the matter is that the M500A is used a great deal more than the 590.

Originally the military specified 3 types of shotguns for use:

The Type 1 was the classic trench gun with bayonet lug and capable of taking a heat shield. This is what we commonly see sold by Mossberg as the M590A1. Sources say about 1000 were purchased by the Army and USMC.

Type 2 shotguns are mostly 18.5 inch barreled M500 shotguns purchased by the Army. Older ones might be bright blued finished, later procured ones would be parkerized. Army choose to go with the plastic trigger group as they very rarely fail and it was decided it was cheaper to replace an entire trigger group than to attempt to repair or rebuild one. These are often standard M500A or M500 MILS shotguns.

Type 2 shotguns purchased by the Navy and USMC are M500 shotguns built to M590 specification using the 5+1 mag tube. Navy likes to buy 17 inch barreled models and the USMC often buys the 20 inch barrel length. These are often called M500A2 or M500M MILS shotguns. Heavy barrels, 590 style mag tubes, bead sights, metal safety and trigger group.

Type 3 shotguns are specified to have rifle sights. It is unknown if the military every bought any.

Navy 17 inch barreled M500
Army M500 where the stock has been replaced with a pistol grip

Let us not forget that the Mossberg shotguns share a common receiver. A 500 could be turned into a 590 by replacing parts, or the other way round. The majority of the parts also interchange with the Model 835 and Maverick 88.

With current use of military shotguns, they have primarily become a breaching tool. Functioning less as a weapon, but an additional piece of equipment for a soldier to carry.

I’m sure this guy just loves carrying two weapon systems.

You would think that breaching with a shotgun would be quick and easy. Shoot the lock, kick the door, enter.

Unfortunately there are any number of things that can go wrong. You need to be at the right angle and distance from the lock. You need to be able to see the lock. If there are multiple locks on the door, you need to be able to engage each one.

There are all sorts of things that can go wrong with breaching. When attempting to breach quickly and/or in the dark it can be hard to get the right stand off distance. Worst of all, you can end up bursting the barrel or having fragment come back and injure yourself or friendly troops.

On the left, a 20 inch M500 barrel, the right a 18.5 inch breacher barrel

That is why the military decided on a fixed breaching stand off. Tests were done on choke based or removeable standoffs but there were failures leading to the decision to go with a permanently mounted one.

This new barrel is approximately 16 1/4 inches in length with out the stand off. The permanently attached standoff brings the barrel to 18.5 inch overall length.

Now, there was a little problem trying to source this barrel. Mossberg is a major manufacturer of shotgun barrels. You can buy all manner of M500, M590, and 870 barrels from them.

590 style threaded cap on the left, 500 style screw in barrel on the right.

Your average Mossberg M500 uses a barrel that screws right in to the magazine tube. The average M590 uses a ring attached to the barrel that and a cap that screws onto the magazine tube. But, Mossberg has made 500s that use the 590 configuration, and 590s that use the M500 style barrels.

Generally, only “tactical” style barrels are available in the 590 setup. All the specialized hunting barrels are set up for the 500 system. Why Mossberg has two different styles of barrels is something I don’t understand. I would have thought they would have picked one system and discontinued the other long ago.

As I said, Mossberg makes all sorts of barrels. You can easily buy a M500 style breacher barrel from their website. You can even buy Mossberg manufactured 870 breacher barrel from their website. But, for some reason unknown to me, they do not list the 590 style breacher barrel for sale.

When I finally decided to pursue this project, I decided I would get the barrel first. I never imagined it would be such a pain in the ass to find one for sale. It finally got to the point where I was expecting to have to buy a whole additional shotgun that came from the factory with this barrel just to get the barrel. Fortunately I got contacted by Pro Patria, who sold me a used barrel as a good price. Around that time a used barrel of this model also showed up on ebay. There are a good many of them out there, but most all of them are mounted on guns.

Changing the barrel on the Mossberg shotgun is very easy. Unload the gun, open the action slightly. Unscrew the magazine cap (or on a M500 the screw on the barrel). Then slide the old barrel off. Slide the new on on and screw on the mag cap.

This new barrel is 1.5 inches shorter than the old barrel. While that is not much, it is enough now to let me case the gun in my 33in rifle case with out disassembling it. That is convenient.

The bead front sight is replaced with a white dot front sight. This sight screws in place of the brass bead and has a white plastic insert. I’m undecided if that is really a worth while upgrade or not. There is a tiny gap between the base of the sight and the barrel and I question if it is any more durable than the bead sight.

But, most of the bead sights on the shotguns I used in the Corps were broken off, so having a front sight is already an improvement.

In the next section I’ll talk about the rail system.


  1. We had every manner of shotgun in our arms rooms over the years. Then when detainee ops was big and everyone needed training on the less than lethals those old guns that had had dubious maintenance at best started falling apart and no spare parts were to be had. The 500s came along but the last weapon procurement I saw before getting out of the Air Force was the 870 MCS. It was supposed to replace all others in our inventory. Don’t know if it did and highly doubt it if so.

    I’ve never been a fan of the scattergun but they’re useful to have around.

    • I really like the 870 MCS, but I almost never seem to see them often in use.
      I’m tempted to make a snide comment like, “The Air Force has all these old weapons because they never use them.”


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