k thanxs for your help

i really appreciate it.
another quick question. Me and another student are having a heated argument over how long the barrel of the tube should be. Saying we have a four foot tube, my suggestion was to cut it in half. This way the three coils are kept close together and has a stronger punch at the beginning.
On the other hand he suggests we use the entire four feet of tubing to gain a greater momentum.
my question is. For this type of experiment, would the projectile travel faster in a short tube with the coils close together, or longer tube spread out?
by saying this, keep in mind that our robot is only 2 feet wide, 1 (1/2) feet long.