just make a dummy projectile that has an hp then move it periodically with an angle offset, then add an if condition if dummy is dead then stop the periodic.
That is essentially what a missile system is, execpt its alot more efficient and configurable, and without the specifics of targeting as in your case.
I do know this - xenforo dropped the ball by not keeping the vbulletin reputation comments as a feature. The loss of the Reputation comments data when we switched to Xenforo really was the death knell for the site when it came to all the users that left. I know I missed it so much and I got way less interested in the site when that feature was gone and I run the site.