Wire brush out the paint/coating, go to your local auto parts store and get a can of Metal-2-Metal metal reinforced body filler, smear on, sand down, paint it and enjoy! Because the body fillers that bond well to aluminum only come in 1 qt and up sizes, expect to pay $45-180 for the body filler, and another 6-10 for the hardner. Cheaper body fillers (fiberglass resiens and puddys) will not stay when you fire the gun, they will pop out. You would need the much more expensive metal bonding fillers or you would be treating your gun daylie/weekly/monthly depending on how much you shoot.
If it bothers you that much, start saving up and find anouther lower, much cheaper and easier.