PGP (paintball marker)

The PGP is a paintball pistol originally manufactured by Sheridan. It is a "Stock Class" paintball marker, meaning that it utilizes 12 gram CO2 powerlets, and has a horizontal feed tube that holds 10 rounds.
History.
The PGP was a direct development of the earlier bolt-action PG pistol, which users often modified with third-party pump handles to increase their rate of fire. In 1984, Tim McMurray, a design consultant for Sheridan, borrowed $14000 to buy all 200 of Sheridan's unsuccessful K Rifle and modify them for sale through his company, McMurray and Sons. Unbeknownst to McMurray, Sheridan had received a larger offer from another party, and one month later returned his money on which he now owed interest. To stay in business, McMurray innovated the pump handle modification using Delrin pump handles and conversion kits manufactured by Stanley Russell and Earon Carter of South Bay Arms and sold them independently through McMurray and Sons. Shortly thereafter, PMI began marketing their own conversion kits as the "Pursuit Pump Kit." McMurray was not reimbursed for nor credited with the design. 
The earliest PGP's were sold by PMI in 1985. These early models were actually Sheridan PG's which were factory retrofitted with knurled aluminum pump handles. Whether by third-party or factory conversions, these are commonly referred to as "PG conversions" to distinguish them from production PGP models. Soon afterward PMI released the first PGP's which were manufactured from scratch for use with factory pump handles. These first generation PGP's retained the knurled aluminium pump handles from the PG conversions, but featured altered main tube geometry, a smaller diameter bolt, and a locking system consisting of a spring and ball bearings mounted within the bolt to prevent bolt rebound during firing. The knurled aluminum handle was eventually replaced with a ribbed aluminum handle, and the faux-wood brown plastic grips were replaced with black plastic versions. A short time before the Crosman buyout of Sheridan, the ribbed aluminum handles were replaced with black ribbed Delrin pump handles. 
Crosman-era PGP's standardized on plastic pump handles, no rear sight, a notched CO2 plug to aid removal by the use of a coin or other implement, and more warnings and information stamped on the brass body. These were designated "P-series" PGP's. The final old-pattern PGP's were the "PA-series" PGPs, which featured the newer cartridge-style valve. 
In 2001, the old-pattern PGP's were replaced by the new-pattern PGP's. While the included manuals still referred to these guns as "Model PGP," the parts list refers to them as a PGP2, and that they began manufacture in February 2001. Thus, this model has interchangeably been referred to as the PGP2001, PGP2k1, PGP2k, or PGP2, and although technically it retains the original PGP designation, usually one of the former is used for clarity when referring to a new-pattern PGP.
PGP bodies and frames were often manufactured and stockpiled for years before final assembly. Therefore, it is not uncommon to see final-generation PA series guns with rear sights, indicating that the bodies were manufactured almost a decade earlier. Lack of available internal PMI and Crosman documentation means that individual models can be difficult to date.
Old and new styles.
There are two main versions of the PGP, the "old-style" version, and the "new" type, which has several upgrades over the original. Crosman started manufacturing the new version after it bought out Sheridan.
The old-pattern 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. P-series PGP's have the old style valve, while PA-series guns feature the "cartridge valve" design.
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. These additions were improved versions of popular home-brew modifications that many owners made to their old-pattern PGP's.