The gas system has a broad operating range and does not require minor adjustments when set properly for the type of ammunition and powder being fired. Gas pressure can increase or decrease with different types of ammunition, ammunition production lots and atmospheric conditions. Proper adjustment of the gas system is needed to prevent violent ejection that results in excessive wear and tear on the rifle. Alternately, it can be rotated the opposite direction, away from the front sight, to open the gas vent, thus reducing the amount of gas pressure applied to the piston rod._ The sleeve is screwed farther onto the gas cylinder toward the front sight in order to block the gas vent reducing its size, thereby increasing the pressure applied to the piston rod. This adjustment is used to regulate the amount of powder combustion gas that is applied to the end of the piston rod. A threaded sleeve is provided on the outside of the gas cylinder in order to adjust the opening size of the gas bleed vent. The gas cylinder is located under the front handguard. Big open port hole + lots o gas pressure=wreaked rifle. Please CLOSE the gas port and open a little until it functions ok. The bottle cap opener on a swiss army knife also works to make adjustments on the gas system of an FN. In addition, the tool is handy to have when adjusting gas on a rifle that has been fired a number of rounds – the gas adjustment sleeve tends to get a bit hot… While many rifles have gas adjustment sleeves that are relatively free to turn (making the tool unnecessary), some have many years of powder fouling that do require a tool (and these should be disassembled and cleaned to make them easier to turn).

The key also has a screwdriver blade sized for the stock end cap screw. The gas adjustment tool (called a “gas regulator key” by FN) is a multi-purpose tool that is not only used to adjust the gas adjustment sleeve, but also to tighten or remove the various FN-provided muzzle devices. Gas Adjusting Sleeve Tool, Original FN Mfg., VG to Exc $14.20

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