Howdy
I picked this one up a number of years ago. SN 158XX. 1906 manufacture.
This one is clearly a commercial New Service. Caliber is 45 Colt.
The only markings on it, other than the SN under the crane, are New Service 45 Colt on the side of the barrel, and on the top of the barrel:
COLT'S PATENTED FIREARMS MANUFACTURING CO
HARTFORD CT. USA. PAT AUG 5 1884 JUNE 5 1900
This is a really big gun, it is the biggest revolver I own.
It dwarfs a S&W Model 1917.
I took it apart once just to see what was inside. I do not expect to repeat that exercise, it was a pain to get back together again. There is no safety mechanism of any sort inside, other than the rebounding hammer.
The 45 Colt cartridge all the way on the right in this photo is one of the rounds made specifically for this revolver. Note how wide the rim is, compared to all the others. This round was made at the Frankford Arsenal in December of 1913.