Thanks for your replies.
oosyrag OK I changed '200' to 'dt*12000', I now have: Self.Bullet.Speed/dt*12000
But it rotates almost instantly, so it's way too fast.
Or does changing the other lines' lerp code (line 75 & 77) influence line 79?
BadMario So used lerp(Self.BulletSpeed,600,1-0.1^dt) as you said, it accepts that line, but should it be exactly like that or did you mean that the 1-0.1^dt part is variable and you posted an example? So that it could be ranging from 1 to 0.1? And shouldn't it be 1-0.1*dt instead of 1-0.1^dt?
I'm a bit puzzled by all of this. Sometimes it feels like I just don't seem to be able to understand code that's beyond a basic to intermediate level. I love making games but sometimes I have my doubts!