While there is a danger of ruining a pup, if you follow the procedures listed in the book, keep your composure, and don't get impatient or angry in your training, you should be able to take your dog all the way through obedience, and even the basics. But you need a good program, and you need to follow it to the letter.
When it comes to basic OB, use treats to teach. Using treats won't ruin your dog. Show him what you want.Then, once he knows what behavior you're looking for, you train. In other words, repeat, repeat, repeat. Only after the behavior is ingrained thoroughly should correction be used. Teach, teach, teach, train, train, train.
Train every day. Twice a day is better, but your sessions need to be SHORT! 10-15 minutes is plenty. Leave the session with the pup wanting more.
I've not seen it, but I've heard great reviews on Jackie Mertens' Sound Beginnings video: http://www.gundogsonline.com/dog-training-books-and-videos/dog-training-dvd/sound-beginnings-retriever-training-dvd.html. Your pup is a little older now, but start from the beginning, and work through it.
Join an obedience training class. 3 years ago, I got my first dog. By the time he was 4 months old, he was pretty good at sit and here. Heel was so-so. We joined a group OB class, and I learned a LOT about how to teach OB, and different drills to work on. The socialization opportunities were excellent, as well. If you are interested in such a group, PM me, and I'll point you to some good ones.
After your dog has learned basic puppy OB, and is a little older, it will be time to "formalize" it, or enforce it. First will be with a slip-lead or choke chain, then a heeling stick, and later, an e-collar. You may have hesitations about the use of an electronic collar, but when used correctly, it is GREAT for communicating with your dog.
Professional trainers can take a dog farther, faster, than the average amateur can. Yes, people have ruined dogs by exposing them to gunfire improperly, but doing it properly is not hard at all! If you're committed to working with your dog every day, for a few minutes a day, and you do your research, you can train a very nice hunting dog. There are lots of resources available to you. Training programs, forums (such as retrievertraining.net/forums), training groups, etc., will be invaluable.