I have gotten a bug report recently from a user of residence and my addon for the plugin Slimefun (see the report for details). I have traced the problem to a missing check for projectiles other than arrows (my bullets are llama spits). In the same report, another issue was pointed out: my grenades do damage. That I found was a lack of an explosion damage check. I also would recommend adding a BlockExplodeEvent handler to handle explosions caused by World#createExplosion. I might submit a pull request for this.