I've got a year old brittany. Took her to the trainer at 8 months. His advice was to build their desire to hunt/kill first, then introduce the guns. Once they're all riled up to chase birds, they'll never think twice about the gunfire. I was there for the first time with a starter's pistol and the dog never slowed down. All she wanted was blood - a friggin' machine. Granted, this is a pointer and not a retriever, but I would think similar thinking would apply. The one thing I've consistently heard is NEVER take them to the gun range. Being kenneled/leashed with all that noise is the worse thing you can do.