If there are two barrels really next to each other, you double tap grab button and will get the two, one will be thrown automaticly, but you will still keep the other barrel even though you don't have the animation of still having it, to get rid of it you just throw it or click on the action pad. The barrels have to be put one then put another one slightly on top
-Graal816688

Lol, Yeah, I was there

If you place a barrel and then place your car right on top of it, then double tap to grab, you grab the car for one second, then if you move, grab or click on action pad it throws the barrel and then spawns the car
-Graal 816688