Not sure of your buget but i have one in my vsr and would suggest this
http://www.airsoftgi.com/mobile/prod...oducts_id=4948
Also depending on what type of metal the stock sear is made out of the piston sear will wear quickly with the stainless piston so
http://shop.ehobbyasia.com/pss10-pis...10-sniper.html
One of theese will be needed soon. If it fits.
Or beter yet
http://shop.ehobbyasia.com/mama-airs...10-sniper.html
I have the deepfire stainless ones but they dont have stock maybe someone else does tho.
The slam fire is a common vsr issue on stock pistons and sears.