View Full Version : Technical: Instructions for Inch-pattern C1 rifles gas adjustment- from Recce

December 11, 2000, 12:53
Courtesy of Recce:

224. Adjusting The Gas regulator
1. Background
a. The force required to actuate the mechanism of the rifle is provided by a portion of the gas pressure generated by the explosion of the cartridge. A small vent hole drilled through the wall of the barrel and leading into the gas cylinder through the gas block redirects some of the gas after the bullet has passed that point. The same amount of gas is tapped off from each round regardless of the setting of the gas regulator.
b. The gas regulator separates the total gas tapped off into two portions: the portion which goes into the cylinder to drive the piston back; and the excess, which is allowed to escape. The more gas allowed to escape the less there remains to actuate the piston and vice versa.
c. The return spring will be compressed by the movement of the breechblock carrier to the rear. The spring tension remains constant, therefore its compressibility can only be affected by varying the pressure on the gas piston or by external factors affecting the backward movement of the whole rifle (recoil). Any factor affecting the recoil of the rifle will therefore directly affect the compression of the spring and will in turn limit the movement of the breechblock and carrier. The following factors are applicable
(1) variable pressure on the butt caused by firing in positions such as prone, standing, etc,
(2) variable pressure on the butt in various positions due to relaxed holding, quick firing, etc,
(3) variation in friction affecting the moving parts due to dirt, and / or sludge,
(4) variation in friction due to change in temperature, and
(5) variation in butt pressure due to the weight of the firer.
d. The correct amount of gas pressure for the best operation of the rifle is that which is sufficient to operate the action under all circumstances. The most suitable setting of the gas regulator is that which eliminates as many of the variables as possible. This is achieved when the rifle is held lightly at the hip, with no resistance to recoil other than the weight of the rifle. The amount of gas required to operate the action will then be sufficient to operate it under any circumstances. Cleaning and lubrication are also required prior to this adjustment.

2. Method
a. Set the gas regulator to the number 4 setting.
b. Take up a fire position standing with the rifle held at the hip, the Left hand holding the forestock and the Right hand at the pistol grip. The hold with both hands must be firm. The butt will not be held into the side by the elbow and no attempt will be made to lean into the shot. Only the hands will take up the movement of the recoil in this position.
c. Fire two warming-up shots and then fire single shots successively with only one round in the magazine each time. After each shot, rotate the regulator to the next higher number until the breechblock is no longer driven back sufficiently to be engaged by the holding-open device. Confirm this by firing another round with the same setting.
d. Turn the regulator to the next smaller number and fire one round to confirm that the breechblock is held to the rear by the holding-open device.
e. Rotate the regulator to the next smaller number for the most efficient setting (optimum adjustment).
f. Once the optimum adjustment has been obtained, no further adjustment of the gas regulator will be made other than normal adjustments necessary to overcome sluggishness due to adverse conditions or progressive fouling due to extended use.

Note: If the gas regulator is adjusted under normal conditions and the rifle is then to be operated in extreme cold (-32C (-25F) and below), the gas regulator should be turned one click to the next smaller number.

C1 sight adjustments (Future)

MANY thanks to Recce for sending this info

1*.....Train Like You Fight: Second Place is NOT an Option.

E.M. (Ted) Dannemiller II