So it would be my guess you have a Model 610 that has a stated barrel length of 3&7/8 inches and so the actual length is measuring at 1/16th shorter, which would not be unusual.

In the case of J-frames with a 1&7/8 inch barrel, Smith & Wesson does in fact state the length as precisely that. However, many in the gun community refer to them as 2 inch.