My Lab-cross is now 6, but was 5 when i started training him. He was very gun shy to begin with, but the more I exposed him to it, the more used to it he got. Just dont let him run away from you. I took a leash and a stake and pegged him to the ground right next to me. After 10 rds out of a 22 he wasnt even flinching anymore. Now a 12g fired wont even scare him. Just be patient, and reward with attention not food...especially if you want him retreiving the kill.