You can probably modify the gun arm with something different with a little Green Stuff. Personally, I don't think Storm Bolters are that great of a weapon for Infantry models. Since he's a Salamanders Captain, I think a Combi-Flamer or Combi-Melta would suit him more. Heck, even a regular Bolt Pistol would work better, IMHO. That way, with the Pistol, you can get an extra attack in CC (assuming your sword is a Power Weapon), and if you go with the Combi-weapon, upgrade the sword to a Relic Blade to make better use the combination.
But hey, that's just my personal take on the Storm Bolter...
Good luck!