That looks liken awesome wee project.... I'm sure you will get plenty of advice and ideas.
One issue (not too bad with. 22) but empty brass is a nightmare in wheels given the right diameters and angles some sort of lip running around he edge to keep any bits and pieces falling off
Check out some of the YouTube videos for rubber ducky shooting at long range, I can see you needing all your friends and families empty drink bottles as floats....
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