Hi pistol blokes

I posted this in the main forum the other day, must've been the wrong place

Just bought a Tau7 Co2 pistol and am reasonably pleased with it...except the hammer spring arrangement. I cant get anywhere near velocity consistency that should be available. 565fps one week......465 the next........530fps one shot.......470 the next!! I suspect the hammer spring arrangement, it looks like a cheap, nasty little affair, the spring doesn't fit the pin properly, the ends are not flat and the spring turns and I suspect, varies the time the valve is open, hence the inconsistency. It also runs out of adjustment prematurely. I have chronoed the gun at 690fps (just to see what it could do mind) but that was weeks ago, now I cant get over 565 with any weight pellet.

Im not after miracles, just about 550 fps to within around 10fps variance would do.

Am I in the right area with my suspicions and am I asking too much of this particular gun.

Anyone?

Many thanks

Barry