Peep sight on HW30S problems?

I installed an import peep sight that I took off a CO2 rifle and put it on my HW30S in .22 caliber, and as I shot it slowly moved back. So after two times using tools to tightening it I think it just may in place. It's a great sight with the rubber eye piece, however it has only one thumb screw to keep it in place. After about 50 or so shots it seems to stay in place. I have a new HW30Scomming in .20 caliber and have another peep sight like this one I'm hoping to use on it. Any good idea on using these sights on springers? With the HW30S be so low power I'm guessing these sight would not work on more powerful springers. Charles
 
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