If a person multiclasses from a Gunslinger into a Gun Chemist, would it be considered to have already aquired the Gunsmith ability if the Gun Chemist "gunsmith" ability states that the gun is identical to the Gunslingers gun obtained from the Gunslingers gunsmith ability?
You'd have two battered guns, but only one copy of the gunsmithing feat. Is that what you're asking?
No, I'm asking if they would have already aquired the gun since it's "identical" (basically the same gun they've already acquired from the Gunslinger class).
You can have duplicate class features, and unless they're said to interact, they're completely seperate. Gunsmithing doesn't ask if you have already aquired a battered gun, it simply grants one.