It was made in the 1970's and the BS means Blued Steel. Probably a Colt Combat Commander. Worth about 600-800 dollars depending on condition maybe more.
Blue Book of Gun values, Colt
Take your pick. Various Colt serial numbers and dates.cut & paste http://www.proofhouse.com/colt/index.html
all colt SAA pistols have serial numbers. If the serial number was filed off then the gun is Illegal to have, and without serial can't tell when made...............
1924
Where did you get that gun?
For Colt, go to proofhouse.com
If you want to know when it was made, you need to call Colt.
The Colt 1917 45 ACP revolver serial is most likely located under the barrel or beneath the grips on the gun. This gun was manufactured in the early to mid 1900s for military use. The gun's serial number gives you an idea of when exactly the gun was made.
about 1973
Look on the butt or the frame.
For Colt series,try www.proofhouse.com
You will have to call Colt to find out.