Colt M1903 with strange sight

I just acquired this Colt M1903 revolver. Decent shape, nice bore, and good lockup. Serial number 200311. The numbers on the crane and barrel don't match.

https://www.milsurps.com/images/impo...DSC_1796-1.jpg
https://www.milsurps.com/images/impo...DSC_1797-1.jpg
https://www.milsurps.com/images/impo...DSC_1798-1.jpg

There are 2 things which I did not notice until I got home and I am curious about. First is the inscription on the barrel;

https://www.milsurps.com/images/impo...DSC_1801-1.jpg

with patent dates of 1900 and 1905. The marking on the side is Colt D.A. 38. I know it is a replacement barrel, but from what with the 1905 date?

Second is this strange rear sight;

https://www.milsurps.com/images/impo...DSC_1800-1.jpg
https://www.milsurps.com/images/impo...DSC_1799-1.jpg

It would seem to indicate someone was trying to improve accuracy and it is very well done. I looked through my copy of Best and didn't see it anywhere, it is probably not a Colt or and Army modification. Anyone ever see something like this?

Comments?

Thanks

Howard

The replacement barrel may have been for the Army Special Model. Barrels up to 6" in .38 Colt and would have the 1905 patent date on it. I have no idea about the rear sight other then someone trying to get a better sight picture. Seems to be well done though.