The most important question is?
Does it work with factory loaded ammo?
If it does, it is your powder choice, or power level, although 19.0 grains AA#9 is getting pretty close to MAX.
Could be your gas system just doesn't like the pressure curve of AA#9.
Maybe try some H110 / W296 or something.
If it doesn't work with factory ammo, you have a gun problem.
Clean the gas piston for starters.
Since it is gas operated, I wouldn't think how hard you hold it should make much difference.
If the pressure curve is right, it should work held against your leg.
rc