LEGAL DISCLAIMER: We never recommend you carry a firearm in a jurisdiction where it is illegal to carry the firearm you are carrying. Always obey the the law of the jurisdiction in which you are operating.
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This article is intended for civilians who consider it necessary to carry firearms in military theatre. Civilians should confine themselves to handguns; other small arms take too much training and are not designed to achieve typical civilian objectives of handgun carry, which are principally self-defence.
The first rule is reliability of a semi-automatic handgun. Modern semi-automatic handguns are designed to be easy to use; it does not matter if you miss the first time because the firearm is capable of firing multiple semi-automatic rounds with repeat pulls of the trigger until the target is disabled. You can even shoot 'from the hip', inaccurate but quick. If 50 per cent of your rounds miss, it doesn't matter. The other 50 per cent hit their target.
So you need your gun's semi-automatic firing mechanism (basically a spring in the gun's magazine which is in the gun's grip, pushing each new round up into the chamber after one is discharged) to be reliable and not get jammed. This is why the Glock and Walther range of semi-automatic handguns, highly reliable, are popular with law enforcement agencies worldwide.
However you must decide what gun works for you; and this depends in large part upon your own personal relationship with handguns. In particular, you must decide whether you are calm enough to draw a firearm without necessarily firing it but without giving away to your adversary your psychological state. Using handguns effectively requires total calm, and hence experience.
A Glock 35 handgun.
A Walther P99, slightly more compact than the Glock but every bit as reliable.
Civilians typically want to carry concealed handguns in theatre. Here are the options. (a) Carry in the inside pocket of a suit jacket. (b) Carry stuffed into the rear of one's trousers. (c) Strapped to one's inside leg just above the socks. (d) Carry in a small shoulder bag that is held under the armpit. (e) Carry in a lady's small social bag. Each method has different advantages and limitations.
Hence for example if your preferred handgun is a so-called AMT Hardballer (also known as a 45 longslide), a large weapon with heavy ammunition and a significant recoil, which means that most users employ it with a laser sight to ensure that the recoil does not reduce accuracy (the weight of the laser sight reduces the upward kickback), then your only option is to conceal it in a bag under the armpit. It is too large for any other kind of concealment. On the other hand, you do not need to fire it more than once, notwithstanding its semi-automatic capacity. It is enormously powerful and will blow a man's head off. It is a preferred weapon of assassins, and it is the preferred firearm of this author.
An AMT 45 longslide 'Hardballer', with laser sighting. This is the gun that Arnold Schwarzenegger used in the first of 'The Terminator' movies.
If you want to carry a large bore weapon, avoid the even more famous IMI Desert Eagle, shown here:
With multiple barrel capacity to take different sorts of rounds, combined with the need for different magazines in each case, the Desert Eagle, although often regarded as the most powerful large bore handgun, is so complex (with a gas-powered recoil mitigation system) as to have a reputation for unreliability. It may jam. Moreover it has a dodgy safety catch, so you may end up blowing off your own genitals. Avoid this gun.
For pure concealability, and reliability in semi-automatic fire, we would recommend either the Beretta Pico or the Colt 380 Mustang. These are the modern versions of the 'Saturday night special' that women used to arm themselves with in Chicago in the Roaring '20's.
The Beretta Pico.
The Colt 380 Mustang
However as any person familiar with handguns knows, the shorter the barrel the less reliable the accuracy. These guns are really only for use at point blank range by all except the most skilled of marksmen. They are quick to fire, whereas a 45 longslide may take 1 to 2 seconds to draw and aim accurately. But those 1-2 seconds may be valuable for your adversary to climb down, faced with a weapon that will clearly be lethal with a single shot.
Another option is a so-called machine pistol, fully automatic handguns with short assault rifle like stocks to maintain accuracy. Machine pistols fire low muzzle velocity rounds with virtually no kickback. They are the preferred handguns of special forces, because there is no risk of the bullet penetrating the target's body and emerging to kill or injure an unintended victim. (Contrast the Hardballer, where this is a significant risk due to the high muzzle velocity of the firearm.) The two best known machine pistols are the Uzi (Israeli) and the Heckler & Koch MP5 (German but used by the British). There are various other Eastern European manufactured machine pistols, but their high muzzle velocities make them unfit for purpose.
The Uzi 9mm
The Heckler & Koch MP5
Neither of these weapons are particularly concealable; but they do have folding stocks and detachable magazines. So it will take several seconds to get one up and running from a concealed location. Immediate use requires them to be strapped over the shoulder using a belt, something not convenient for civilians.
The principal reason why civilians should not use assault rifles is that they leave heavy bruising on the shoulder due to recoil, unless one is extremely used to firing them. In the war in Ukraine, Russian troops are inspecting averred civilians' shoulders for evidence of bruising to establish whether they are really soldiers or mercenaries.
Moreover as a civilian you never have need for the firepower and muzzle velocity of a contemporary assault rifle, the purpose of which is to penetrate enemy armour. They take several seconds minimum to activate and aim well. Plus they are heavy and they cannot be concealed. Stay away from them.
The AK-74, the principal assault rifle used by the Russian Armed Forces.
The AR-15, the principal NATO assault rifle.
If as a civilian you prefer to carry a non-lethal firearm (or less lethal), you cannot get better than a gun firing baton rounds (so-called rubber bullets). These are high velocity gas powered short barrel rifles that fire marble-sized steel ballbearings covered in a thin layer of rubber. They do not penetrate clothes or flesh so are unlikely to be lethal. However they are incredibly painful - much more so than being shot with a conventional firearm - and they can break ribs and other bones. They are semi-automatic and designed to be fired quickly from the hip.
They are lawful in France and several other European countries. Buy them in France where they are available 'over the counter'. They can be concealed in a bag under the armpit.
A gun firing baton rounds (or 'rubber bullets").
These guns are excellent for crowd dispersal, by reason of the shock and pain and the relative absence of risk of death in firing them into crowds. If you are looking to deter rioters and you do not wish to use lethal force, baton rounds are the weapon of choice.
A baton round to the head may crack the skull. A baton round to the neck may crush the windpipe. Do not aim baton rounds at people's heads. They are perfectly effective even fired at the legs; the target will collapse in pain, as though someone had kicked them in the shins with a steel toe-capped boot.
Finally, do not use guns firing capsicum or Tasers in theatre. Events move too quickly in theatre for these deterrence or incapacitation based firearms, and they just don't work.
We wish you good luck if you are a civilian entering theatre. Do not rely upon the expertise of others; their priority is the saving of their lives, not yours. And never use a firearm in theatre save in a genuine belief that your life is in danger. That is the legal test lawyers will hold you to once you have exited theatre, which it is likely that you will. So if you discharge a firearm with lethal consequences, expect that to be the standard you are held to. It is often a difficult call.