The case contracting would cause the opposite of sticking. That is one of the knocks on steel cases; they don't contract as much as brass and therefore lead to harder extraction. The timing of good extraction is such that it should not happen until the chamber pressure had dropped enough to allow the case to contract some. If you have the gas up too high, it could cause the extraction to start early, leading to more stress on the extractor as it pulls out a case that is still expanded hard against the chamber walls. Extreme case of this, and you could rip the rim off a case. This will also happen if the case is stuck hard enough for another reason. I can't think of a way that not enough gas would directly contribute to cases sticking. Cases sticking may *become more evident* through lousy extraction if your gas setting is low, but having the gas low will not be a direct *cause* of the sticking. (I believe that to be correct and hope it makes sense.
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One simple test to see if your cases are really sticking, would be to just turn the gas all the way off and fire a shot. Pull charging handle. If it is difficult to extract, your cases are sticking.
See thats what I would think would happen from my basic knowledge of how shit works!!, BUUUT, knowing that the timing is as important as the amount of gas, I think that the opposite is actually happening.
the round goes boom, bullet travels past gas bleed, and starts to fill piston, bullet leaves barrel and pressure drops. (heres where it gets tricky) since there was not enough gas bled off into the piston, there is still too much pressure on the cases which would in turn mean that the timing was basically not right in the whole system. There is still enough gas to extract and cycle the action, and even rip the case rim off, but the timing of the contraction of the case is too slow and thus it sticks.
If the gas were higher then more gas could be sent into the piston and thus allow pressure drop a millisecond or so faster and let that case contract enough for reliable extraction. In reality, the piston aint gonna move any sooner with more gas, and the bullet is long out of the barrel before it does start to move, but it will move with more authority and have more gas acting on it.
If you add other mitigating factors like polymer case coatings, differences from round to round and crud build-up, then you start to get a better picture of the whole situation.
Now, I dont know if this is actually the case, but it would seem to explain why it's doing what it's doing.
your method of testing may show some result. but with the sticking only a sporadic thing, it may be many shots before you got a result.
