what part actually hits the bb?

[boydo]

thanks

 

[Nutster]

The air

Unless I'm mistaken, nothing actually touches the bb?

 

[jcheeseright]

no part of the gun hits the BB, propulsion is entirely by a push of air or expanding gas.

 

[Mike636]

The only part that will touch it is the hop up nub as it passed through the hop up.

 

[Tariq]

The only part that will touch it is the hop up nub as it passed through the hop up.

Indeed. And this is not a hit, but just a brushing touch on the side to create backspin.