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Can't wait to see the after pics. I've seen quite a few guns over the years that were rusted because of contact with blood, mostly from deer. It always looked a bit different than regular rust. That S&W 40 has that look...Hmmm

 

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I don't think this is the same but worth a look.
Walther PP PPK Hammer

 

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Or try calling this place.
https://walther.parts/

 

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Numrich Gun Parts stresses that point on their catalog site. I liked the old way of ordering parts from them. Call it in and if they had it they sent it C.O.D. That was a last ditch try at a long-term project. They also sent out a notice if they did not have it.
Roy

C.O.D., now there is a blast from the past. I used to order lots of things like that, especially car parts from Summit and Jegs. I think companies getting burned on shipping costs for non payment and UPS drivers getting robbed stopped that.