There are a couple good sites. First thing is to ID production. Its an actual Walther gun, hence the AC code. If you follow this link it will download a guide to production codes to determine approx. Manufacture.
pistole38.nl.server3.starthosting.nl › tech
There are some magazine ID sites to check if those are the correct style of manufacture for that particular pistol and whether they are properluly serial numbered to the gun or not.. You will also want to look up the holster. Type, maker, etc. They can even help determine if it was likely issued with that particular gun. That is your starting point. Considering that good original holsters seem to run as asking prices $140-175, as well as values for original mags (asking over $100 each) it is important to get that footwork done before valuating it.
EDIT: YOU NEED TO DISSASSEMBLE AND CHECK THAT BARREL, LOCKING BLOCK, SLIDE, AND FRAME ARE ALL DATE CODED THE SAME.
One thing you may want to ask is if the pistol was a WWII begin back by a veteran. Generally soldier were suppose to get a "certificate" that the War trophy was of no Military intelligence value. From what I understand is there was no specific War Department form. The certificate could be a locally produced "form," letter or certificate. Military Regulation, War Department Memo W/370-3-43 dated 22 July 43, USAFFE Circular No. 21 5 March 44 and Circular No. 267 were the general guidance for war trophies. I have found of these "certificates" located in the bottom of the holster of the gun where the GI can easy access to the authorization. The certificate could add value to the gun.
Values begin around $400 and run on up to around $2,000 and probably beyond. I have an original 1944, (I forget the manufacturer) unissued, never fired (except for possible factory testing) P38, originally ensconced until after the War in Switzerland by the Nazi's. I would call it an NRA 100%, (except 100% NRA ranking doesn't actually exist and it has import marking). To an assiduous collector this import marking means a lot. To a normal collector it means nothing. It's still the real thing and it's really clean. I also have a shooter -- nice gun, historically important in the realm of firearms development and politically, accurate, deadly, and fires relatively inexpensive 9mm, feeds any 9mm well.
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