I just got a 336 R.C. that belonged to my grandfather. According to oldguns.net it was manufactured in 1968. It had some smith and wesson brand 30-30 ammo with it with a S&W headstamp. I never saw S&W branded ammo, just thought I'd share.

Perhaps some interesting information on your ammo

http://www.trapshooters.com/threads/cartridge-head-stamp.112698/

A grandfather's rifle is a class weapon. You're lucky.

Real classy.