Let me put it to you in crayon.
Anything you propel vertically, that is in the nature of a toy, or an experimental, rocket or aircraft - > less likely to be a problem.
Anything that you propel other than vertically, if it's not an obviously low powered toy, even if it doesn't look like a gun,
will almost certainly be a problem of some kind.
If we are talking rocketry, then you may care to do a keyword search of the CASA website for "rocket"