Yup...if Factory 3 inch Barrel, then would be a Round Butt.
4 inch Barrel ones were Square Butts.
Possibly some Special Order 13s could be otherwise.
Personally, I think they should have offered any variation a person could want, of Barrel Lengths from 2 to 10-1/2 inches, and in either Butt syle, and with Target Sights as an option.