Hello:

Wobbly gas piston should not be a problem except a loose fit between the piston and the cylinder will allow gas to escape around the piston - reducing the rearward impulse and potentially requiring a higher gas setting to run the gun. This type of fit/wear issue is why there are multiple gas nut channel sizes in the original design.

I did not clearly communicate. I have never seen a gas nut where HA has drilled out all 4 of the gas channels to oversize... usually it is just one. So, when you say you are going to use setting 4... if HA drilled out channel #2 to oversize... 4 might not actually be allowing more gas than the drilled out 2 setting. You would need to determine if your barrel gas port is reamed out to be larger than as issued... and which if any gas nut setting has been drilled out to oversize... AND.. compare the gas channel sizes in the gas block itself (channel that feeds the gas nut) on the barrel to see if that channel was also drilled out oversized... all of this is just to determine if the gun has had its gas system modified to allow more gas into the cylinder to power the semi auto internal cycling. You need to find the combination of elements that allows the most gas and test this for feeding function... if max gas does not sufficiently recoil the internals to allow for reliable feeding... it could still be multiple contributing elements... spring issues... not enough gas, magazine feed lip/round positioning issues... if hand cycling the action provides reliable feeding of rounds, then running the gun should too. If not then each element(s) need to be investigated in the search for the cause(s).

"but what is the risk of using the gun on 4 all the time?" This is the scenario I mentioned regarding gunners running their guns over gassed... it can lead to damage of internals over time... in the case of a semi auto of HA design... potential crushing of the striker spring comes to mind. All of my focus on the gas channel sizes is to allow you to accurately determine what combinations really provide more or less gas... and whether the barrel and gas nut have been modified for semi auto use in a HA semi auto system. If you have a barrel or gas nut that is unmodified... this could be part of your problem in adjusting the amount of gas needed to power the HA semi design. Systematically assess each system element against a known original configuration part or specification. Good luck!