There are two main versions of the PGP, the "old-style" version, and the "new" type, which has several upgrades over the original. The latter is commonly called a "PGP2001" or simply "PGP2." Crosman started making the new version after it bought out Sheridan.
The old style PGP is made of three tubes of soldered brass, powdercoated black. A trigger frame is attached to it by two screws, and the feed caps are also secured. The rear cap is removed by twisting and pulling out. It has no external velocity adjuster, so the gun must be taken apart to adjust it, either by cutting the spring or adding shims. It has the old style valve, which is considered more efficient than the newer "cartridge valves."
The new PGP has an external velocity adjuster, and a plastic feed cap that allows for quicker reloading time. However, it is commonly lost or broken. The quick changer allows for faster CO2 changes than the old style.