Closing as won't fix. The bounce-off-solid code is pretty complicated, and in order to properly calculate the correct angle of reflection given the angle of the surface it's collided with, it's necessary to push it out a few extra pixels. Normally this is not noticeable since it only adjusts it for the one tick a collision happened. However your code forces the bullets in to the solid every tick, so the adjustment becomes an increase in speed. The 'Bounce off solids' is simply not designed for this, and you'd probably need to use the Physics behavior exclusively to properly simulate this type of interaction (including sliding, friction etc).