Heck, that ain't a stupid question, BS Billy.
There is a sequence of numbers that will determine which frame size you have.
In fact, with the S/N sequence you can determine the model of ANY Ruger, either long gun or handgun.
It is on one of the Ruger websites, if you wanna see where ALL Ruger S/N's.
If'n you can't get it searched...
I'll look it up & get back to you.
MG