i pick it up in the second or third chapter when you walk into the parking grage but after "dead man walking "when you fall out of the copter i cant equip it ever again and it shows as locked. the thing is that after i picked it up on the nova in the grage i put it on the hammer and it showed as unlocked but after that dead man walking mission it shows as locked for the rest of the game and is also locked in the stats for 100 percent compleation along with 2 other attachments that i got but never unlocked in the stats either.