Tuning FX Super Swift / Adjustments

I have a FX Super Swift and would like some information on this rifle. I can not find the "Super Swift" on FX's website. 

My rifle has a loud bark when I have the "power adjuster" on high. I think I'm shooting supersonic..

My question is: the set screw located just below the magazine holder handle straight in line with the bbl. 

I must remove this set screw to remove the action from the stock. 

Does this screw have anything to do with velocity ( hammer tension)?

How tight should this screw be against the spring? 



 
This was

this was the set screw that fits in the stock. Brass slotted screw is below (above in picture) this one 
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