Odd Markings on Colt 21/28 Navy

[JBabb]

This just hit gunbroker.  Markings on the left side of the receiver are very odd.  Stamping forward of the Model / Serial number markings looks to be "GTR" and there looks to be some additional markings of "CAL 45 M1928" towards the rear of the receiver. 

https://www.gunbroker.com/item/1094666290

[Got Uzi]

Glad to see they are still up to their usual tricks of keyword spamming and calling everything they sell “rare” 

Does seem odd that the caliber was marked like that, but one would have to look at its history and maybe where it was required it?

[Merry Ploughboy]

GTR -> Grand Trunk Railway ?

[Not to be confused with GFR -> Grand Funk Railroad, whose cover of "Locomotion" once was a wedding reception favorite tune.]

[TD.]

I took some pictures of Colt NO 6718 in late 2018. I found the markings on the right-side receiver to be is a very unusual and stated these markings would probably detract from value. What really got my attention was the "GTR" mark. I now wonder if this is the inspection mark of Capt. Garland T. Rowland, US Army. I do not know for sure but will say the "CAL 45 M 1928" markings, also on the left side receiver, appear military in nature. What I really hate is the parentheses markings around the nomenclature. I do not mind the dot or punch mark to the bottom right of the overstamped number "8" as I have seen this before on military Colt's. Could NO 6718 have been a Colt submitted to the US Army for testing and later returned to Auto-Ordnance Corporation and sold commercially? 

Based on the information in Gordon's 6th Edition, it appears NO 6718 was originally sold to Sheriff's Department in Kansas but quickly returned to Auto-Ordnance and later sold to a prison in Boston, Massachusetts. Could all of these 'extra' markings on the left side receiver have been the reason for the rejection of NO 6718. Whatever the reason, something obviously did not make Sheriff Robinson happy about NO 6718. 

When I took pictures of NO 6718 in 2018, I can show it was equipped with an original two-piece NAVY actuator and a bright or in the white Colt bolt with the number "18" stamped in the bolt body. Also, while the butt stock appeared to be Colt, the anchor mark was not visible. If interested in NO 6718, I would recommend a thorough inspection as it appears some parts have been changed out over the years. I also have information where NO 6718 was sold on gunbroker.com in early 2018 that I will share with anyone seriously interested in bidding on NO 6718. 

All good stuff!!!