No letter but with a serial number of 5700-'n-something it's probably 1910-1911.
A pistol this ratty would spoil your whole menagerie.
I'm thinking I posted it's tale some years ago here on Defensive Carry, among other places. Was a fun acquisition. Anyway, here it is again.
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"Pancho Villa" the Colt Model 1905
My 1905 is far from perfect. It is complete, original, has the proper magazine, and is in good order, but the blue has turned to a soft brown patina except in a few protected areas. The original finely checkered walnut grip panels are so worn that most of the checkering is completely gone.
When I worked for a bank in Glen Rose, Texas I had a Mexican lady who was my customer and who also used cleaned the bank. After her brother had died she spoke of a Colt .45 automatic she had around the house that had been her brother's gun. She said it had previously been her grandfather's pistol and that he'd brought it with him when he came up from Mexico. I love old guns and envisioned an old beater of a U. S. Army .45 so asked her to bring it by sometime. She said she would and that in fact she'd thought of selling it as she was concerned about having it about the house with her grandchildren. I didn't much think I'd want it as I had some decent military .45's. One day she brought it by my office wrapped in a rag inside a paper sack. I'm sure my chin hit the desk when I unwrapped it to find a Model 1905. Only about 6200 were ever made. Of course I was interested in purchasing it and told her so. She was hesitant as it was a family heirloom. I said: "that's ok, I don't blame you for wanting to hang on to it. Why don't you let me clean it up for you so it may be better preserved?" So I cleaned it , oiled it, and gave it a thin coating of RIG. I returned it to her and didn't think any more about it.
Several years later, and after I'd left that bank, I ran into her and she asked me if I still wanted to buy her .45. Well of course I did so I took possession of the old pistol.
I've read that the early Colt automatics with the dual link "parallel slide rule" design were unsafe to fire. The design doesn't share many of the later 1911's attributes. After examining the design closely I determined that if the slide velocity wasn't too high that the gun should be fine to fire. The .45 ACP as it was introduced in 1905 featured a 200 grain bullet, so I prepared some 200 grain lead SWC handloads with a moderate charge of Unique. I worked up from the minimum listed charge weight to a middle-of-the-road charge which gave good function. The old gun is as accurate as my other military .45's and has never jammed. I wouldn't subject it to a lot of use but am willing to take it out for occasional exercise.
I've never indulged in naming my firearms with the exception of this one which I call Pancho Villa. It just has to be one of his original guns. At least that's my story and I'm sticking to it. I keep intending to spring the hundred bucks for a Colt factory letter but haven't gotten around to it.
As may be seen it's missing a couple of grip screws. I'm certain that the same sized screw fits several early Colt semi-auto pistols but how often does one stumble across any such pistol or screws? If anyone has a suggestion for a source I'd be grateful to know it.
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Pancho Villa "roars into action" at a "meet-n-greet" in Tennessee a few years back, hosted by a member of a private forum I'm on. A fairly prominent S&W forum member's putting it through its paces while I man the camera. The smoke is from the bullet lube used. Notice the ejected cartridge case in mid-air in this "action shot."