Is it a numbered part? If yes, laser welding is an option. For laser welding service, I recommend Microarc Welding in Worcester MA:
http://microarcwelding.com/
They offer excellent service, including post-welding micro-machining. Cost some $$, but it's definitely a new experience. There are a few gun makers in the area, they use laser welding service for prototype modification, much faster and cheaper than changing the "jigs".