I am 16 years old, 165 lbs, and this thing is still a viable beast of a spring! I can lift about 50 pounds rather easily, so I thought this would be a BREEZE to prime... and BOY was I wrong! With a rail priming assistant from FoamTechnician, this thing is NEARLY IMPOSSIBLE to prime at 40 lbs (18kg). I need to prop it against a hard surface and push down pretty damn hard for it to fully prime. It's too heavy of a "run n' gun" prime for your "average nerfer", but I still like it due to its sheer power of 170 FPS. For these reasons, I am giving this product 4 stars. It works, but it's not for everyone...
P.S. DEFINITELY prime the spring with the catch before putting it in the gun. Even priming it outside of the blaster is hard, and you'll need to use a hard surface for that priming as well. Also, just sticking the spring in like a regular spring mod is a death sentence! That thing will explode on you in seconds if you aren't careful...