Falling Projectile

You should be able to achieve this by doing something like this:

• Create a ranged weapon that fires your projectile normally, with the creative tab set to None because this item is just so that you can use the projectile later and wouldn't actually be used by or accessible to the player
• Make your actual weapon (probably of the Item or Tool element type) and have it perform a summon command on right-click at the players look location. You would have to use the "look position of entity" blocks and the join text block to create the command.

Unfortunately Imgur seems to be down right now, so I can't upload a picture of an example. Sorry if this was a bit obtuse.

Imgur is working again, so here is an example:

Link if the image doesn't show: https://imgur.com/a/uFfyOSb