Yes you can make a living being a gunsmith. That being said do not plan to do so by working a 40 hour week. Mr Bonar and cntryboy1289 both gave some very good advise and both are speaking from experience.
Now back to the 40 hour week. Most likely you will not be able to hire anyone to help when you first start out and even when you are able to you may not want to. So that means you do your own paper work, ordering of parts, talking with customers on the phone or by e-mail and sometime after doing all this you must do the actual work on the guns. You might as well figure putting in at least 25 hours a week doing all the things it takes to run the business, so if you want to spend 40 hours working on guns you are now working a 65 hour week. To be successful you will most likely be working 80 to 100 hours a week.
Next you want to learn all the skills you can such as welding, machine skills (mill and lathe), as much finishing work as possible. The more work you can do in house the better. Remember when you have to farm work out you have to deal with that persons time frame and the amount of skill they have in doing the job.
Here's some things that were taught to me that may help you make it as a smith. Do not price your work to cheap trying to under cut everyone in the business. If you do it's almost a sure bet you will start doing poor quality work for the simple reason you do not feel as if you are making enough off the job at hand. You must set down figure what you have invested in your shop and machinery, than figure a fair labor rate that will help you survive in the business.
Do not count on making much money from parts unless you are having your own manufactured.
Be honest with your customer and do your best to provide customer satisfaction.
Do not claim to do work that you can't do.
Do not try and cheap out on parts as it will come back to haunt you. It does not cost that much more to use high quality parts and your customers will be happier in the long run.
Above all else do not knock another mans work to try and sell your own. This was taught to me at a very young age by my Dad. His words were " if you have to knock another man's work to sell your own than there must be something wrong with what you are selling".
Good luck in your endeavors and I wish you well in the business.
Regards
Bob Hunter
www.huntercustoms.com