The title should be everything you need. Specifically the piston and the spring guide are absolutely brilliant, especially coupled with a lycan 90 degree sear replacement. The only fly in the ointment is the bundled spring. That M170 turned my sniper into a crew served weapon. It's next to impossible to cock without somebody's assistance and follow-up shots are impossible from a prone position. Keep in mind, I pre greased everything, before mounting the spring and piston. Having said that, when I was able to actually arm the thing, my chrono couldn't see the BBs flying out, they were so fast. If I were to wager a guess, I'd say the overall speed was way over 160 m/s with a 0.2 BB. All in all, a very nice kit - it would probably be a better idea to bundle it with something along the lines of M130-M140. M170 is way too much and completely unusable.