The forcing cones on older guns, like your Parker, were designed for shells using fiber wads. The forcing cones needed to be more abrupt to get the fiber wads to seal in the bore. Plastic wads seal much better and benifit from having a more tapered forcing cone. The forcing cone reamers that Brownells sell have nothing to do with with hull being made of paper or plastic. They are designed to change the shape and length of the forcing cone. The recoil reduction Brownells is refering to comes from a longer, tapered forcing cone. The chambers have to be measured with a gauge. A dial caliper will not work. Find out what the chamber length is first before you do anything. Above anything your ammunition needs to be the correct length for your chamber.
Also, paper hulled shells like Federal Gold Medals or the older Champions, are loaded with plastic wads. Just because it has a paper hull does not automatically mean it has a fiber wad. Gamebore cartridge loads some of their cartridges with felt wads. Check out Gamebore and get your chambers measured.
