Keep in mind that a gunsmith is an odd blend of both wood and metal worker. With the wood side having a strong lean towards carving and custom "non square" shaping. And to be fair a lot more focus on the metal working side of things.
Then the "gunsmith" part is tacked on over top of those two foundation stones. Otherwise you're simply a parts changer. So if you don't have a combination wood and metal shop to start with that would be a good place to start. It's far more than just book or online learning.