I have no idea what was used to blast this pistol. Generally, one can "blast" with anything that will make through a blaster. Sand, carborundum, steel shot, glass beads, and eggshells are some of the media of which I have heard. I'd wager that something in the range of eggshell would likely be appropriate for a blued finish, but remember, this is a physical process and the energy of the medium is transferred to the surface, the collision knocks off material.
The surface finish of a Luger was originally established by milling, filing, or sanding, and I'd include buffing if postwar Mausers count. Under magnification, you can see exactly what the finish was established with, as all these processes leave their own distinctive evidence. Blasting of course leaves evidence, too, in the form of tiny, tiny dents; their size depends on the blast medium's aggregate size, aggregate hardness, and its velocity. Anyway, blasting seems to clean and even out a pistol's surface to the naked eye; but look closely and you will see the difference--and the damage.
For simply removing a finish, I'd go chemical in approach. Stripping of any sort removes molecules from the surface, it's just a question of how deep and how finely the top molecules are affected; chemistry gives the results while removing/changing the least. Ever dip a silver or brass piece to clean it? You noticed that clean does not necessarily mean shiny, and shiny is another matter.
I guess if we're dealing with a shooter, all is fair game, depending on how comfortable you are disturbing history, and the extent to which you're doing it. Personally, I'm leaning toward going over this AE chemically, to clean it of anything but steel; and then abrasive processes which will reestablish the "grain" found in hand work. There will be no way to do it without softening the stampings, because material will inevitably be removed; but I'm prepared to accept the required minimum of this.
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