[ithacaartist]

The barrel to upper fit, as Rich mentioned, is an interference fit, and not easily accomplished with a file, it really needs a lathe to make this adjustment. Sending the assembly to G.T. for the adjustment--which amounts to the same moves you'd make to change barrels--is something I'd recommend. A ~9mm barrel rod might not be that much of a problem...but I'm afraid the competent "regular" 'smith would not have the barrel vise, receiver wrench, or receiver reinforcing block on hand unless he has properly changed Luger barrels previously. They'd need to be sourced or made from scratch. These are specific to the job to prevent damage to the parts. Moreover, each different barrel length would present a slightly different taper, requiring specific inserts made for the taper being addressed. G.T. has already put in the "head-scratchin'" time, which saves subsequent clients from at least part of the expense of creating the tooling. A few bucks for shipping and a week or so to wait are well worth it, IMHO!