Low velocity limit often means that the valve isn't staying open long enough to let out enough co2 to get speed up. I've never had much luck with Lapco internals (esspecially the hammer) and really hard valve springs. Try a lighter valve spring.
Others have had different results but I think they are from warmer climates
I agree with CJ about the quality of CCI's parts. I only use LAPCO internals in 1 of my 6 Nelson based guns.