Take the speargun and defeat corrupted beach crabs

[speedyandy]

lately I get to 47 of 50 killed and cant get completed even using rifle or my weapon I have had this problem from day one of the game.

[DarkArekkusu]

I've had this issue a lot lately as well. It takes a lot longer to finish the quest using your normal weapon too. I'll get to about 15-20 out of the 50 kills needed, and then the gun randomly stops working. Even throwing it away and getting a new one doesn't fix the issue.

[GerryStew]

There is a bug in this quest, where is you kill one of the large crabs with the gun, it will not work any more. you will need to drop the quest and restart it at that point. Make sure you do not kill one of the large crabs with the gun, just the small ones, till you get 50, then kill a large one with your regular weapon to complete the quest.

[Hazgaz]

Kill the little ones first then kill big one last.  If you kill the big crab before the 50, it stops working.

 

[Udunnome]

6 hours ago, Hazgaz said:

Kill the little ones first then kill big one last.  If you kill the big crab before the 50, it stops working.

 

or invite someone to party and let the other guy kill the mobs for you :D

[Shautru]

This happened to me but it let me finish up with normal weap.

[Valthan]

I was on my summoner and when the gun stopped working, I just made the cat do all the work. (Which isn't any different from normal, let's be honest...)

[Metleon]

I think my gun stopped working when I picked it up so I just used my normal weapon to destroy them. Granted, I was probably 10 levels above what they intended me to be. 

 

I tend to find that the weapons you pick up aren't really worth it unless they're single use.