Shotgun Mini Shells

12 ga Shotgun Mini shells by Aguila®™

Modification & Testing of Mossburg®™ 500A 12 ga Pump Shotgun


12 ga Shotgun Mini shells – Manufacturer Data
  • This new type of 1-3/4″ 12 ga shot shell (1-1/2″ OAL loaded) was developed as part of the innovation drive carried out by Industrias Tecnos SA de CV from Cuernavaca, Mexico, manufacturer of “AGUILA” ammunition. The original idea was to create a new shot shell with law enforcement and military applications in mind. The new cartridge would generate a milder recoil (less shoulder punishment and faster reacquisition of the target after the first shot is fired), would provide more firepower (being able to load 12-14 rounds in a 20″ bbl shotgun) and would be ergonomically friendlier (being able to grab a big lot of shells with one hand and comfortably place them in the pocket). Due to its smaller size one police officer/soldier would be able to carry about 40% more rounds than regular shot shells. All this, while providing the necessary power for Police/Military work.
  • Early in our development work it was clear that this new round would hardly cycle semi-automatics while also having difficulties in feeding some pump action shotguns flawlessly. This lead us to consider the development of a weapons system which would include a new shotgun (more about this later) especially designed for the Mini shell. In the meantime, after some testing we realized that the WINCHESTER™ 1300 series cycles MinishellS flawlessly (12 rds in an 18″ bbl “Defender”); MOSSBERGS™ and REMINGTONS™ needed a minor modification in their elevators to produce similar results.
  • All Types of MinishellS are loaded to SAAMI specs according to 12ga shotshells of regular size, namely 2-3/4″ or 3″ in length. This means that regular shells and MinishellS generate the same pressure in the chamber of 12ga shotguns.MinishellS should NEVER be used in signal/flare guns or any other firearm other than 12ga caliber SAAMI approved shotguns. Failure to comply with this may result in injury or death to the user or others.
  • While we were producing shooting prototypes and focusing in the law enforcement/military markets, information about this project was somehow leaked to the civilian market in Mexico which became intrigued by the new cartridge. Due to this, we decided to do some merchandising by selling MinishellS in a 7-1/2 birdshot load; results turned to be quite encouraging. The reason was that the milder recoil encouraged female and young shooters to fire the same 12ga shotgun carried by their older more experienced shooter, who in turn found the lighter shot load (18 grams) a bigger challenge to shoot skeet than with regular loads.
  • CENTURION ORDNANCE, INC., TECNOS’ U.S. wholly owned subsidiary started importing and selling MinishellS in birdshot and slugs loads in the U.S. market. The reaction was similar to that in Mexico, plus CAS participants who found the tiny shot shell very convenient to reload. “Coach guns” with automatic ejector are normally not permitted; WINCHESTERS M1897 cycles them fairly well.

The Above information comes from the manufacturer. Please see their site for more information.

Reloading at best is a 1 second lag in firepower. That speed is based on a lot of practice. Reloading, is the time to advance. A person can advance 21 feet in 1 second……42 feet in 2 seconds.

The moral to the story…You should always bring more than 1 gun to a gun fight. The Military brings martial arts, knife, handgun, and a  rifle. You see the difference.  You can never have enough ammo or backup.

The idea for the modification came from being to cheap to purchase a 10 rd Mossberg pump 590 aka military/police setup for two matches a year.

MY MOSSBURG 500A Modification  

aka – Mossberg Mini Plug


You assume all risks, known and unknown for this modification. This will void your warranty. This could result in miss feeds. Failure to feed has been reported by others but not by using this modification. I did not have any failure to feed during testing and shooting in matches. Additional testing by independent sources needs to be performed as to FTF.

I compete with my Mossburg 500 in USPSA Shotgun matches. These matches usually have stages with following characteristics:

Points divided by time so you cannot dilly dally.  Reloads are the largest time factor. With the modification I can carry more in the tube. Using regular or magnum 12 ga shells  the tube magazine holds five shells and one in the chamber, giving a total of 6.


Steel knockdown targets ranging from 8 inch diameter steel plates, to larger 4 foot size knockdown steel. There are stands that hold regular clay pidgins and mini pidgins. These could be as close as 10 feet and as far away as 50 feet.    


Cardboard regular USPSA target and / or USPSA 1/3 Target set at 40 to 60 feet. Scored based on pellets x Score on A-D ring


Cardboard regular USPSA target from 20 feet to 100 feet . Scored based on A-D ring

Photo of Regular Rifled Slug compared to Aguila mini slug









Minishell Buckshot


A small plastic/ nylon spacer attached to receiver with set screws.  The Mossberg-Mini-plug was designed out of nylon. Easy to cut and mold with a dremel tool. Then attached to the Mossberg receiver with two self tapping screws going through 2 undersized holes in the receiver, which in turn taps into the Mossberg-Mini-plug.

With the spacer in place you can still load regular size shells one by one if needed. This is a removable feature. Requires 2 holes drilled through the receiver. Once in place everything performs in real world situations. The matches I have used the mini shells have a total round count of at least 60 rounds. Way more ammo then you will ever use in a home defense situation.

Like any modification, it will void your warranty. I will not be held responsible for your modification.

Dimensions for the Mossberg-Mini-plug.   









Picture of Mossberg-Mini-Plug

minish4     minish3

Pictures in receiver

minish5 minish6





















    First Test was a basic cycle test. I used a foam block with heavy metal foil tape as a prototype.

    Cycle test with nylon Mossberg mini plug passed with flying colors with 200 rounds cycled.


    1- Cycle Test.  Holding shotgun down, up, and at different angles.

    2- Shoot 10 shots total waiting 15 sec between each shot.

    3- Shoot 10 shots total rapid as possible.

    4- Shoot 10 shots total rapid as possible, mix shot, slug, then reload 10 and shoot rapid as possible.

    5- Shoot 15yds shot for pattern test twice

    6- Shoot 25 yds slug for analysis using Modified cylinder and rifled choke

All tests passed.  No misfire of any kind. No miss feeds due to  Mossberg-Mini-plug

Pictures of 25 yard test of the Slug, below    

Exif JPG 422











Pic 1a.

25 Yard Sandbag rest   Mossburg Shotgun 12 ga Pump

Modified Choke  Wolf 12 ga slug Standard size.

Not too bad of a group 3.5 Inches.

Exif JPG 422










Pic 1b.

25 Yard Sandbag rest Mossburg Shotgun 12 ga Pump

Modified Choke Aguila Minishell Slug

Seems to open up a bit. 11 inch group.

For personal defense works fine out to 25 yards.

But for the long shots in USPSA there is a margin of error.

Exif JPG 422











Pic 1c.

25 Yard Sandbag rest  Mossburg Shotgun 12 ga Pump

Rifled Choke  Aguila Minishell Slug

Seems to tighten up a bit.   to 9 inch group.

For personal defense works fine out to 25 yards.

But for the long shots in USPSA there is a margin of error.



I came out to the range to shoot a shotgun match. Everyone took bets from;  It won’t have enough power to knock down the steel, ha ha ha…  Sure they work? it will jam just watch …etc. 

Time to put up or Shut them UP!.   In a quick test in front of the Range Officer, crack-a-towa- the Minishell shot did have the power to take down the steel.

The Minishells shot worked great all match.  The slugs have no stabilizers , ie. rifle grooves. so once you get out to a distance the slugs tend to spread a good bit compared to regular rifled slugs. I even tried a rifled choke to add some spin.  In a match I missed , or had a low D ring score on the targets at 80 feet. I did some tests and took photographs. The difference is obvious.

A regular size shell can be inserted as needed one by one. For example add a regular size rifled slug for the far away shots.

I no longer use the mini shells in matches due to the new rules on power factor. The matches I did shoot showed the modification worked in the heat, dust, repetitive firings, and staged scenarios of those days.   




The testing and matches proved the rounds are manufactured well and offer reliability.

There are limitations for the Slugs, which come into play once you get past 60 to 75 feet range.

The difference I found was the diameter of the slug. Regular slugs fit tighter in the barrel. The factory

might be able to improve this.  25 yards is well within a practical home defense parameters.

The ability to load a regular rounds is a plus. Especially for a 100 yard shot.

I personally opt for more ammunition. In this case 40% more for a total of 10 rounds at the same weight as 6 rounds.

The rounds are 30 to 40% less powerful, less recoil, still effective at home defense ranges.

This set up could work for Military or Police.

So take a look at your shotgun, and if it is a pump, you may be able to make the modifications and up your on board firepower by 40%.  The Aguila site has information on other shotgun modifications and an actual Shotgun designed from the ground up for the mini shell.   


More testing as to the (FTF) failure to feed or jams needs to be performed by independent multiple sources. I did not have any FTF, even in rapid pumping mode.

  • More testing as to the design of the Mossberg-mini-plug, and improvements needs to be performed by independent multiple sources.
  • Change the two screw system in the prototype to a punch pin.
  • Manufacturer should investigate the diameter of the slug compared to other manufacturers slugs as to tighten the fit to decrease the spread at 25 yards.
  • Manufacturer should investigate the addition of rifling on the slug compared to other manufacturers slugs as to to decrease the spread at 25 yards.
  • Manufacturer should investigate the use of more 1 buck and less 4 buck in the buckshot round. 1 buck is considered the smallest round to use to be effective.
  • Additional test photos of shot pattern and buckshot pattern to be included in next revision of document.




Shotgun Shell type Comparison
By USPSA Power Factor
Min Power Factor to knock down steel is 125
Aguila Mini Shot  Reg 3 Dr Shot
FPS speed 1175 FPS speed 1145
Projectile Weight 277.78 Projectile Weight 492.00
Power Factor 326.39 57.94% Power Factor 563.34
Aguila Mini Slug  Reg slug
FPS speed 1250 FPS speed 1600
Projectile Weight 385.808 Projectile Weight 438
Power Factor 482.26 68.82% Power Factor 700.8
Aguila Mini Buck  Reg OO Buck
FPS speed 1200 FPS speed 1200
Projectile Weight 304.2 Projectile Weight 484.2
Power Factor 365.04 62.83% Power Factor 581.04
Buck Shot Pkg size wt grains
four 1buck rounds 0.3 40
seven 4buck rounds 0.24 20.6
Total Wt grains 304.2
7.62×39 123g 5.56
FPS speed 2400 FPS speed 3100
Projectile Weight 123 Projectile Weight 55
Power Factor 295.2 Power Factor 170.5
.45 cal HG 9mm cal HG
FPS speed 920 FPS speed 1125
Projectile Wt 230 Projectile Wt 124
Power Factor 211.6 Power Factor 139.5


Mossberg, 500A, 590 Mossburg®™  O.F. Mossberg & Sons, Inc. – Firearms, Shotguns, Rifles

Aguila®™ Ammunition                      Aguila Ammunition / Centurion Ordnance, Inc.

Wolf®™ Ammunition                         WOLF Performance Ammunition 

Federal®™ Ammunition                    Federal Premium ammunition

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