Well, you could strip down the gun, sand it and hit it with a couple coats of Krylon and it would probably look good for a while, but solvents used for cleaning the rifle would eventually remove the paint in various areas that it contacted creating a mess and you would end up with the rifle looking worse than when you started.
There are spray & bake on coatings specifically designed for firearms, they are a safer bet as most are resistant to oils & solvents.
A third option is to have the aluminum parts hard anodized, a plating company will be able to do this and it really should cost you no more than about $65 to have a few aluminum pieces done.
Any way you go, the end product will look as good as the prep of the parts prior to finishing, for the bake on finishes to adhere well you really need to blast the parts first.