12 gr. valves:
What seems to be happening with a 12 gr. Crosman valve is that the piercing pin acts as a valve stop, limiting the distance the valve can be opened. The valve cannot open any farther than the distance the piercing stem can move forward and that forward movement is halted by the 12 gr. jammed into the valve seal.
(BTW: if you really nut down on the end cap, the 12 gr. will compress the seal and reduce the seal’s inner diameter. The piercing pin will then contact that seal’s now smaller inner diameter, use up it’s energy in friction, perhaps fail to pierce the cartridge on your first try, and shoot slower. Tighten just enough to keep the gas from leaking to get full speed and if that seal has already been squished closed, replace it.)
A once the hammer spring opens the valve to the limit, why does a heavier spring still gain some power? Because the valve has to close by forcing the hammer AND the spring tension back down. What a stronger hammer spring seems to do is increase valve dwell.
Past a certain point, the gas escaping the valve isn’t adding much to the pellet’s speed, just squirting gas out after the fact, making the gun loud but not faster.
QB’s have the same results, but to a lesser extent, because the 12 gr. isn’t jammed up quite so close to the piercing pin (they aren’t jammed into a seal on the valve body because the tube itself is pressurized). Still get to the point where whacking the valve harder doesn’t do anything good.
As a QB experiment, drill the neck out of an empty 12 gr. cartridge as wide as you can (leave it more than paper thin as it still has to hold it’s length). BE SURE ALL METAL SHAVINGS ARE OUT OF THE CARTRIDGE!!!! Drop that drilled 12 gr. in first, neck down, then a full 12 gr. pointed up for the end cap to pierce. Piercing pin assembly is still in the valve, so it acts as a gas flow restrictor, but will ba allowed to move out farther because it won’t contact the 12 gr.’s seal. You’ll see at least a small jump in vel. from the valve being allowed to open farther.
IF you wondered what bulk filling your QB would give you in speed, The above experiment would be very close to that speed using a standard QB valve.
Haven’t figured out an easy bulk fill speed test for the Crosman’s because of their design.
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If you want faster, then look to smoothing and enlarging the gas passages rather than whacking the valve harder and harder. Want the gas to reach the pellet in a large burst, not a long line.
Think of 3 tubes filled with BB’s. One tube is shorter, but 1†inside diameter. The other tube is longer and 1/4†inside diameter. The third is just like the 2nd (same length and inside diameter) but has some “kinks†and roughness inside. they all hold the same amout of BB’s. Take the plugs out of the three tubes at the same time. Which drains all its BB’s the fastest?
