If you stand at this specific location by the taser, you can see the dispenser with the AK 47 behind the bars floating in the air.
I spent a couple of days thinking about how to get it and came to this method.

1. Grab the barrels from the first floor and move them to the second floor.
2. Make a tower that you could get up on it. Be extremly careful: every movement around the barrels can move them and ruin the tower.
3. Climb the tower, then do the following in the .gif.
4. Jump on the wall on the first floor, next to ak47.
5. Аccelerate, jump on the invisible surface and jump again. After that grab the AK 47 in the air. It could take a few tries.

Thank you for reading this small guide. I hope it was interesting!