The JC Higgins 33 was made by High Standard for Sears in the mid 1950's.
Marlin Firearms
100-1000 usd
Gun Shops And Internet!
Marlin
50-160 USD or so
Numrich Arms
www.histandard.info
The J C Higgins model 20 pump shotgun is one of the finest pump shitgun out their made from 1947 to 1962 two and three quarter inch 12 gauge game loads no 6 shot have always worked well for me. I prefer federal ammunition or Winchester that's your choice
The JC Higgins Model 20 is a well-made firearm. Provided you have it checked by a competent gunsmith, it can handle any standard 12ga 2 3/4" shotshell. If the gun is not choked 'FULL' you should be able to use slugs.
you may find some info at the savage arms website.This was the maker of your shotgun,savage/stevens.
50-260 USD or so