Go to the mission where you have to shoot a doe and find the nontypical buck. From where you start, go to your left and go up the hill. Here comes the boring part, stand still for 10 min. and you'll hear a jingle noise. Immediatly look up (you have to do this fast or you'll miss it). If you have a S.A. shotgun you can shoot him down and he will crash his sled into the hunting lodge. Go up and talk to him and he'll take your gun and steal your truck.
Press BLACK, BLACK, L, BLACK, X, Y, B, A.