"Traditional" shooter help

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I would appreciate some input from anyone that has a very successful "traditional" shooter. By "traditional", I mean single rotating shaft usually with 2 wheels on it and a curved usually 2 pipe back frame for the ball to roll up.
"Successful" means shoots easily close to tower.

What wheels (size, material) did you use ?
How are you powering it (motor(s), direct or geared etc) and about what is the no-load RPM ?
About how much compression on the ball does your shooter apply as it pulls the ball through ?

Thanks