Enter Von Croy's apartment, go to where the Rig 9 handgun is. do not pick up the gun first, that brings the cleaner. instead, go to the ammo clip right next to the column (where the dining room table is). I found that if you pick up this magazine first, it wont dissapear until you pick up the handgun. I picked up 60 magazines, and could have done many more. As soon as I got the gun, when I went back and picked up that clip, it then dissapeared.