Ok so you need a missile that is a size and shape fitting another sprite you are using, correct?
In that case, it would be helpful for you to link a copy of the weapon image that said missile should be launched from...
Basically you want a projectile sprite, not an ammunition drop item...
I'm sorry if I have suddenly confused you, just ignore that, it's essentially me thinking...aloud...(in text?)
Anyway, please post the weapon you need the projectile to fire from, so that it may be fitted correctly.