When a body is fired,when does the force on it ceases to act

When a body is fired from a gun , there are four forces acting on it:

1) The forward driving force from the propellant. This force ceases to act on the body immediately it emerges from the gun barrel.
2) gravitational force - which acts downwards on the body and never stops acting on the body. Before it is propelled , during its travel up the barrel , while it is in the air and finally at rest on the ground, the body is subjected to a downward gravitational force
3&4) Air resistance/ friction force which acts on the body while it is moving. Travelling up the barrel , air resistance and friction forces act on the body. The friction force reduces to zero when it leaves the barrel. Throughout its movement it is subject to air resistance force. This ceases when the body is stationary.

The net force is zero only where the acceleration is zero.
Which means only after it has stopped. And is no longer moving.
The net acceleration then is zero.

at the end of the barrel.