i have a hinged spanish small ring bottom metal that i am going to use on my Yugo 24/47 in 6mm. the hinge on this bottom metal is like a door hinge, that is to say, proud of the bottom and not inlet like an argentine or aftermarket. I do not have a tig welder, but a mig. welding with regular mig wire (gas shielded, not flux core) what kind of color should i expect should i decide to blue this gun? my other option was to duracoat it professionally, in which case, coloring wouldn't be a worry, correct?

with metal finishes other than bluing, what kind of fit can the parts have? if my hinge is really tight and the gun is duracoated, will the coating chip off where the barrels of the hinge come together? (again, think door hinge)

I don't use anything but TIG for gun work, but I bought a spool of ER70S-6 in the event I ever seen a need to use a MIG. This is basically the same fill rod I use when TIG welding and I haven't had any color problems with bluing.

Can't help you with the duracoat questions because I don't use it, but I don't believe a mismatch with the color of the metal would be any concern.

Any product that adheres to a surface can close critical tolerances. Depending on how tight the pieces are, there could be some interference.

Mig is Maybe it's good??

As in tig is the only way to go unless you have a big area to fill and can afford the clean up.