The gun force depends on your current velocity, so you get the most boost when firing just after jumping/moving in the direction you were firing. So when just shooting while standing still wont boost you nearly as much. This was done so you could fire in the opposite direction to cancel out any momentum you had. So kind of like breaks to help stop yourself from slipping off an edge. But in practice it can just end up making things feel inconsistent and even more frustrating then it already is. If I had the chance to redo some stuff I think I would've had one gun instead of two, make it a bit more powerful, and cut the "breaks" mechanic entirely.