Over the last few weeks I’ve gone through several design iterations for the Nerf Cannon. This is mainly due to my insistence in trying to use a continuous rotation modded servo to move the darts into position. I have finally given in and used a stepper motor. This is something I should have done right from the start with hindsight.
However, the darts are now lining up perfectly with the gun barrel every time now and the 3D printer is busy beavering away printing out what I hope will be the final version of the gun. Once the gun is finished and fully working I shall post up a video of it in action.
Medway Makers 
Do you have the model of stepper you are using as I am having a similar problem. I was thinking of using a 360 servo with position feedback.
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