1873 colt single action army revolver
Follow the instructions in the owner's manual.
Try e-gunparts.com
see the link below for the owners manual. The Marksman Repeater is a 4.5 .177 caliber pistol not a 5.5 .22 caliber pistol.
If you don't have a manual, find a good gunsmith.
go to the link below.
I have a model '66 and the round type is .25.
If you don't have a manual, get help from a gunsmith
If you don't have an owner's manual, find a gunsmith and ask for help
see the link below for the Owners manual.
Steve's pages might have one.
Follow the recommendations in the owner's manual.
If you don't have a manual, find a gunsmith and ask for help.