At four months of age you still have plenty of time to introduce the gun to your pup(when you get one). Let him point, bump and chase birds till he is just plum crazy over birds.(get him wired 220 about birds!)Then when you know that birds is all he has on his mind, then you fire a cap gun or 22 after he is a good ways out from you chasing the bird he has pointed. If he shows no sign of discomfort from the shot the move on up. 410 or 20 ga etc.Whatever guns you have access to.