S&W holster 21 signifies the "Blazer" model, which is probably S&W most prolific model. HoweverI don't find a # 78 handgun size listed for the Model 21 in any of my S&W leather catalogs. I do note the other size numbers beginning with the digit "7" are all for various Colt handguns, so perhaps # 78 is a newer style holster for a Colt. S&W made their own holsters from about 1969 to 1983 when they sold their leather company to Gould & Goodrich. Your holster appears to be designed for something like a .22 Auto pistol, judging from your photos. I would put the value in the $20 to $30 range. Ed.