As someone who has worked on these guns, I'm gonna up and say they're pieces of crap. The way Ares designed it doesn't make any sense to me, and they're clumsy/awkward to manipulate.
We had the stock sear that holds the piston break under 30 rounds, with the stock spring.
As many others said, The only good replacement is this:
http://www.tntsniperproshop.com/prod...110_en_5457646
And you basically have to buy the whole kit (pain in the ass to install, as it requires drilling/tapping holes), or your piston won't lock properly with the sear, as the stock cylinder is not really compatible with this kit, It slam fires if you aren't careful in pulling the bolt back.