European Black Market of Guns and how does it work?

Im in argentina, i can buy any rifle bolt action or level action rifle, i can buy any handgun or revolver, i can buy shotguns and i can buy 22.lr semi-auto rifles.
Usual burger semiautomatic rifles are Banned.
We can own primers and gunpowder but it is controlled by the state.
It is very easy to get a illegal firearm, i have owned one in the past, it was very easy i bought it from the cops.
Also i own a 380 pistol and a shotgun of 12 gauge.

Fine gun, those are not legal here.
Seriously any relevant in modern warfare rifle is illegal, but easy to get if you have money and take the time to get yourself one.

In some countries in Europe are illegal.

Dont forget homemade grenades. Knives molotovs and clubs you dont need to start out with a gun just a weapon to kill someone who has a gun.

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Find a dodgy russian gun runner

You can make a basic pump shotgun with spare parts, just make sure the pipe you use for it is steel that is rated the same or better than those used in manufactured shotguns. Get a length of 8mm thick steel and use a plasma torch to cut the slats and grooves needed for the slide mechanism of the pump. You can use either make thin plastic sheets yourself to cut into shells or use paper, just make sure that when you use paper you don't store shells for a long period of time because the powder can sweat nitro glycerine.

You can literally load steel ball bearings into the shells if you want but getting a batch of lead shouldn't be heard and you can use strike-anywhere match stick heads for primers.

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Why not make a single shot? much simpler.

Can you even buy ammo in Yurop?