On how much leakage is tolerable:
The graph below is an experiment in which the leakage area increased and the pressure in the carrier cavity (cylinder) was measured. Line (1) is confusingly listed as zero (0) leakage, when it is actually the system in nominal condition, which for reference, is an equivalent leakage area of about 0.700 mm^2, that includes the barrel-front sight, front sight-gas tube, gas tube-carrier key, carrier key-carrier, and carrier-bolt interfaces. The other lines, (2), (3) and (4) are the cavity pressure with the listed leakage area. The leakage area was controlled by increasing the clearance between the gas tube and carrier key. Under normal conditions, the gas tube-carrier key interface accounts for about 80% of the total leakage.
(2) is about 2X normal leakage
(3) 3X
(4) 5X
The resultant bolt/bolt carrier velocities are:
(1) 63.32 fps (100%)
(2) 49.97 fps (79%)
(3) 44.29 fps (70%)
(4) 37.73 fps (60%)
This graph is based on a standard M16A1 rifle length gas system, for a carbine length the cavity pressures will be about 10% higher.
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