calm down... you get that achiement like many others in any mode you play. if you play multiplayer you can get it too . go into the training mode and you can set up a match of any type o fyou want anywhere and whatever weapons you need. also a good way to get the specific weapon achievements

 

that's a good idea havoc! I'll just create a custom match with each gun until I get the achievement.

 

i wa sin your shoes. i had 14/15 and couldnt figure out what i was missing then i realized i was missing the boomshot. so i set up the match and got my achievement.

 

ill be on in the next 5-10 mins if anyone wants to play through the rest of the campaign with me. im at the end of act 4.

 

rrasco my buddies coming over...if we decide to jump on I'll shoot you a message and get on there with you

 

sweet, getting on now!