If you’ve the ammunition which can usable to fire from the weapon then you can easily able to use a weapon which has the ammunition property for making ranged attack. You can expend one piece of ammunition each of your attack with the weapon. Normally, drawing the ammunition from the quiver, case or else from the other container is one of the parts of attack. But at the battle ends, you can recover half your expended ammunition by receiving a minute to search the battlefield.
If you would like to use a weapon which has the ammunition property for making a melee attack and also you treat the weapon like an improvised weapon. A sling should be loaded to the deal any of the damages when used in this way.
Blowgun 5E Weapon Attributes