Crosman Pell Master 700 .22 CO2 rifle balanced valve HPA conversion
Posted: Sat Dec 14, 2024 11:43 pm
Yet another vintage pellet gun resto-mod 
The Pell Master 700 is a somewhat unique CO2 rifle that was first manufactured by Crosman in 1967 and only made for four years. Unlike most similar devices pellets are loaded through a rotary tap rather than a bolt, and the hammer and valve are in line with the barrel, with the gas flowing through the hammer into the breech.
The original rifle was charged with a 12 gram CO2 cartridge and could fire around 40 shots at around 6 ft lbs of muzzle energy.
Here it is disassembled:
Some detail shots:
Naturally I wanted power power so I went with an HPA conversion, The CO2 piercing cap was replaced with a chamber extension with foster type fill nipple and the firing valve was replaced with a balanced design. This reduces the force keeping the valve shut and therefore prevents valve lock at higher pressures with the standard hammer setup.
Chamber extension fitted:
Balanced valve parts made to fit in the original valve body:
Firing cycle animated:
At 1200 psi higher muzzle energies are possible although as air is much less energy dense than carbon dioxide, the number of useful shots is reduced to around five. In this case the following muzzle energies were recorded:
Shot 1 - 762 fps - 18.4 ft lbs
Shot 2 - 733 fps - 17.1 ft lbs
Shot 3 - 657 fps - 13.7 ft lbs
Shot 4 - 605 fps - 11.6 ft lbs
Shot 5 - 563 fps - 10.1 ft lbs
The average muzzle energy is more than twice that of the original, and in spite of the considerable drop in velocity over 5 shots, accuracy remains good enough for plinking at 30 feet as shown in this footage:
The Pell Master 700 is a somewhat unique CO2 rifle that was first manufactured by Crosman in 1967 and only made for four years. Unlike most similar devices pellets are loaded through a rotary tap rather than a bolt, and the hammer and valve are in line with the barrel, with the gas flowing through the hammer into the breech.The original rifle was charged with a 12 gram CO2 cartridge and could fire around 40 shots at around 6 ft lbs of muzzle energy.
Here it is disassembled:
Some detail shots:
Naturally I wanted power power so I went with an HPA conversion, The CO2 piercing cap was replaced with a chamber extension with foster type fill nipple and the firing valve was replaced with a balanced design. This reduces the force keeping the valve shut and therefore prevents valve lock at higher pressures with the standard hammer setup.
Chamber extension fitted:
Balanced valve parts made to fit in the original valve body:
Firing cycle animated:
At 1200 psi higher muzzle energies are possible although as air is much less energy dense than carbon dioxide, the number of useful shots is reduced to around five. In this case the following muzzle energies were recorded:
Shot 1 - 762 fps - 18.4 ft lbs
Shot 2 - 733 fps - 17.1 ft lbs
Shot 3 - 657 fps - 13.7 ft lbs
Shot 4 - 605 fps - 11.6 ft lbs
Shot 5 - 563 fps - 10.1 ft lbs
The average muzzle energy is more than twice that of the original, and in spite of the considerable drop in velocity over 5 shots, accuracy remains good enough for plinking at 30 feet as shown in this footage:
