I am looking to take on my first fix up firearm. I am looking to buy a used gun that I can replace parts on fairly easily and parts are readily available. I'm hoping to also be able to put upgraded parts on. I have not done any upgrades on my firearms before, but I do have a background in industrial maintenance. I am looking for suggestions on gun models to look for. I'm leaning more towards a rifle, possibly a shot gun. Not too much a pistol. Tips are appreciated also.