Many semi-automatic weapons have a simple sear on the back of the trigger that catches after firing, ensuring only one round is fired at a time, until the trigger is pulled again. If you remove this sear with a hacksaw, file or power tool such as an angle grinder you can turn an often perfectly legal semi-automatic into an often illegal fully automatic blaster that empties its magazine way too fast, costs a small fortune in ammunition, and is almost impossible to fire accurately. The process takes less than 10 minutes.
So I mean, yeah, it’s very very easy and cheap to do. It’s just totally pointless most of the time unless you recently discovered an enormous stockpile of worthless dodgy ammo in your doomsday prepper uncle’s basement you want to burn off in one afternoon. The fact of the matter is that fully automatic weapons are pretty damn useless, and in reality most semi automatics are too. In my personal experience hunting, semi automatic .223s lack the stopping power for medium sized game like goats and fellow deer and larger caliber semi automatics have too much recoil and you might as well use a lighter, cheaper, shorter and more precise bolt action rifle. In this random internet person’s opinion, the only valid semi automatic tools for hunters are rimfires such as the 10/22 for quickly dispatching rabbits and small game, and shotguns.