What module are you using? The Adventure game one?
I any cases :
Check your projectile object... set "player weapon", both Edge and Solid reaction should be " Destroy Me", set acceleration and speed, and a bounding box. That's all (don't set any of the action step flags).
Then if it's a platformer game:
You have to set the "ignore gravity" flag for the action step 0.
If your projectile still doesn't move AND you're making a plaftormer game, you maybe forgot the important part about the "UserSubroutines.asm" and "HandleHorisontalInertia.asm" scripts ( 3/ and 4/ in the tutorial http://www.nesmakers.com/viewtopic.php?f=3&t=1703) for fixing the "igonre gravity" issue.