Airsoft "grenade launcher" spring

Here is a grenade launcher like spring system for airsoft. Please note that I didn't print it yet so I can't give you any estimation of it's range (could go from 3meters to 30meters), moreover it depends of the hop-up you will give it.

So it's able to shoot 15 BBs per shot thanks to 3 barrels with 5 BBs each. The rubbers are usefull for 2 things : they avoid BBs to get out of the barrel without shooting and they give a hop-up effect for a better range. The model's length is 17 cm.

What you