I have no idea how this isn't a well-known bug and how come it wasn't fixed yet.
Sometimes, alchemer-line shots simply don't apply damage. Even though you see them colliding with your target, they take no damage, regardless of your target being well in their range. There is also the similar problem where despite your bullets showing a range very close to the Antigua line's, your bullets will never apply damage at the very end of the shown range, despite the bullets actually colliding with the target.
Video of the range bug, the random not-applying-damage is very hard to record:
http://www.youtube.com/watch?v=58QG_nI1N_Q
OOO, fix them please. I have a VH dmg vs every family alchemer collection and it's REALLY annoying and horrible, this bug.
It's because the 'damage' part of the shot is activated after a short delay. If an enemy moves fast enough, it can be hit by the projectile and move out of the way during the 'damage delay'.
You can see this a lot with Devilites. They get 'hit', dodge, and evade all damage. If a rebound bullet flew out at the Devilite's original position, you have yourself a 'dud'.
In rare cases, if you aim extremely closely to a target without hitting it (when aiming to the side of a target), the bullet will play its contact animation without ever having touched the target. The actual bullet will be invisible, ghosting past what it looked like it hit, still able to land a hit on something else.
You can see this more often with Skellies, or other slow/stationary foes. I'm pretty sure it only happens with basic shots, not rebounds or charged shots. If it does happen to those as well, I've never seen that happen.
So, uh, yeah. I hope it gets fixed myself. Just wanted to shed some light on things.