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Discussion Starter · #1 · (Edited)
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This has been debated before with no actual answer past our educated guesses. The above gun is a late, 2nd Generation Colt, NRA Comm from 1971 production. The trigger guard on this gun had turned purple by the time I bought it. I had the trigger guard reblued right after my purchase and it again turned purple.

I had an 3rd Gen production gun, 1st year production, (see photo below) that did exactly the same thing and when reblued, again turned purple.

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This is a pair of the NRA guns from 1971 that are 1700 guns apart for serial number. The "purple" trigger guard is obvious (and really ugly) by comparison.

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The "plum" colors were indicative of the earliest Kimber of Oregon rifles with cast receivers.

This is a photo of the back side of a Colt trigger guard that has changed to the "plum" or purple color.
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A few years back I bought a couple of over size, rough cut, totally unfinished, but already serial numbered, Colt trigger guards off Ebay. This morning I spent some time fitting one of them to my "plum" colored NRA gun.

This is what I started with. By the serial number stamped on the trigger guard it is a Custom shop gun from 2004. Judge for yourself if Colt is using a cast trigger guard. I have no doubt in my mind the current trigger guards are an oversized casting that is then machined to fit, casting pits, mold marks and all.

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Discussion Starter · #2 ·
By comparison this is a USA made USFA trigger guard that has not been fit to a gun or final finished. It is not cast but CNC cut, from bar stock. If you own a Standard SA, it is pretty clear where their CNC program came from.

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I've always understood that turning a plum color had to do with incorrect bluing salt solutions or something like that. Pythons had an issue with cylinder release latches some years back doing it...I've seen FN Mauser sporting rifle receivers from the early '60s that way as well.
 

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The line in the center is typical of a forged part. Cast parts like Ruger uses can be made virtually ready to polish. Forged parts need to be machined to fit.
It looks like a mold parting line in the photos above. A forging mark looks different. Much wider typically.
 

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I have no clue, but I would love to hear the ultimate answer. Like Snidely, I have owned several pythons, government models and a few saa that had parts change to plum. And, I might add, I don’t like it🤮
 

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Discussion Starter · #9 · (Edited)
Forgings don't have bubbles and pits in the metal surface. Well at least least good forgings don't.

Forged parts are machined to spec. Colt frames are a classic example of that process. Parts that cast can also require machining and usually do. If you are using current MIM technology for the casting, the part can be and usually is, virtually ready to use once out of the mold.
 

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Really neither here nor there, but I've seen a number of S&W barrels turn plum. Especially the run of 26-1 guns in 45 colt made to commemorate the Georgia State Patrol. Weird.
 

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Discussion Starter · #11 ·
Lots of issues could cause the plum coloring. Could be the bluing mixture or temps. Can also be that particular steel alloy or its hardness, or simply a cast part that is different on any one of those same things. Kimber of Oregon took a beating back in the day as their Pre '64 Model 70 style actions were really nice but machined from cast parts...not forged as the original Winchers were. The plum color was what everyone was so stressed about. If they had just stayed blue and many did, no one would have bitched.
 

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It looks like a mold parting line in the photos above. A forging mark looks different. Much wider typically.
While not a Colt trigger guard this does show the difference in regards to the cast Vs. Forged line.

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Not the best pic but one of my Colt has a plum colored trigger guard. I had these pic in the computer.
I was always lead to believe this os from being a cast part ( metal issue) or the bluing mix was incorrect. Obviously if reblued and it still won't match the rest of the revolver sure points to a metal issue to me.
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As mentioned, probably has more to do with alloy and bluing than being cast. Model 1897 and early 1912 Winchester barrels were noted for turning purple after rebluing. Local gunsmith ran bluing temperature higher for the old Winchester barrels to prevent this. In the 1950's and 60's Colt had this problem with some of their Government Model slides.
 

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I have blued hundreds of guns. The ones that turn purple are usually cast. Some alloys may be more prone then others to turn this color. It is not the salts. Browning A5 shotguns turned black like nobodys business. Some alloys would not blue at all, stainless and whatever Winchester used on the post 64 94s. I have read many explanations for them and all are different. Single shot shotgun receivers always turned purple. The parts may be black for a while but will usually return to purple in short order. The pictured parts sure look cast to me. Modern hot blue is a very thin layer that offers very little protection as compared to the older true rust blue. Look at the old Lugers and Broomhandles to see how well they have held up. True rust blue is a thicker layer of true rust that has been converted from red oxide to black oxide by boiling. It usually etches the metal just a little giving that soft slightly grey appearance.
 

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If I'm not mistaken, I believe one my 3rd Generation has the cast trigger guard, but it might be the 1985 SAA.
I've had both apart to changed mainsprings and I'm sure one of them had a trigger guard that looked like an Uberti trigger guard with the casting line which are definitely cast.
 

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I used to own a Ruger M77R that was made in 1980. The receiver had turned plum color by the time it was less than 20 years old. I also owned a Winchester Model 70 Featherweight that was made in 1982 that the receiver had turned plum from where the barrel screwed in back to about the end of the loading port.

I was not surprised to see that the Ruger, with a known investment cast receiver had changed color. The Winchester was another story, it too took about 20 years before the color change was noticeable. I'm thinking the change on the Winchester may have had something to do with the forward end of the receiver having different heat treatment than the rear.
 

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Pre war Colt OP frame forging in my collection. The forging line would be thin as you can see.

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