1. A DEVICE FOR COMPENSATING VARIATIONS OF THE FIRING TEMPERATURE OF PROPELLANT POWDER CHARGES FOR PROJECTILES TO BE FIRED FROM A RECOILLESS RIFLE BARREL HAVING A PROJECTILE RECEIVING AXIALLY EXTENDING BORE PARTIALLY DEFINING A PRESSURE CHAMBER FOR THE PROPELLANT POWDER CHARGES, COMPRISING: AN INERTIA MASS OF SUBSTANTIALLY THE SAME DIAMETER AS SAID BORE TO DETERMINE ONE AXIAL WALL OF THE PRESSURE CHAMBER; CONDUIT MEANS INCLUDING AT LEAST ONE GENERALLY AXIALLY EXTENDING OPENING SPACED RADIALLY INWARDLY FROM THE OUTERMOST DIAMETER OF SAID INERTIA MASS FOR EXTENDING THROUGH SAID INERTIA MASS AND CONNECTING SAID PRESSURE CHAMBER FOR THE PROPELLANT POWDER CHARGE TO THE ATMOSPHERE FOR EXHAUSTING A PREDETERMINED FIXED AMOUNT OF THE PROPELLANT POWDER CHARGE GASES FROM SAID PRESSURE CHAMBER TO REDUCE THE PRESSURE WITHIN SAID PRESSURE CHAMBER A CORRESPONDING PREDETERMINED FIXED AMOUNT; ADJUSTMENT MEANS OPERABLE TO ADJUST THE EFFECTIVE CROSS SECTIONAL AREA OF SAID CONDUIT MEANS TO SELECTIVELY CHANGE THE FIXED AMOUNT OF GASES EXHAUSTED IN A DIRECT CORRESPONDENCE WITH THE TEMPERATURE OF THE PROPELLANT POWDER CHARGE TO MAINTAIN SUBSTANTIALLY EQUAL PROPELLANT CHARGE GAS PRESSURES FOR PRODUCING SUBSTANTIALLY EQUAL PROJECTILE STARTING VELOCITIES REGARDLESS OF THE TEMPERATURE OF THE PROPELLANT POWDER CHARGE; SAID ADJUSTMENT MEANS HAVING A RELATIVELY FINE ADJUSTMENT ONLY BETWEEN TWO LIMITS; SAID ADJUSTMENT MEANS AT ONE LIMIT OF ADJUSTMENT PRODUCING A SUBSTANTIALLY ZERO CROSS SECTIONAL AREA OF SAID CONDUIT MEANS TO SUBSTANTIALLY PREVENT THE EXHAUSTING OF PROPELLANT GASES FROM SAID PRESSURE CHAMBER OPERABLE TO PRODUCE A STANDARD GAS PRESSURE IN SAID PRESSURE CHAMBER AT THE LOWEST FIRING TEMPERATURE TO BE ENCOUNTERED; AND SAID ADJUSTMENT MEANS AT THE OTHER LIMIT OF ADJUSTMENT PRODUCING THE MAXIMUM CROSS SECTIONAL AREA OF SAID CONDUIT MEANS TO EXHAUST THE MAXIMUM AMOUNT OF PROPELLANT GASES FROM SAID PRESSURE CHAMBER OPERABLE TO PRODUCE THE STANDARD GAS PRESSURE IN SAID PRESSURE CHAMBER AT THE HIGHEST FIRING TEMPERATURE TO BE ENCOUNTERED.