My son had a similar problem. He would thow up projectile over my shoulder onto the floor. It seemed like a lot of milk. Try to get an idea as to how much it really is by pouring an ounce of water on the counter. Sometimes it looks like more than it really is.
I had an overproduction problem. My ds would feed from one breast for four hours and it was still too much milk for him. He wanted the comfort of nursing so he would nurse, throw up, nurse, throw up. I read that the muscle that closes the thoat is weak in babies that's why they spit up so much. My son stopped spitting up so much at 8 months. Even at 1 year he still spits up sometimes.
If your son is gaining weight well I wouldn't worry about it. It's just a pain to clean up all the time and of course more laundry to wash. If you are still worried you could talk to your doctor about it. Hang in there