bw15 carbine rubber hopup replacement?

[mikersutcliffe2303]

Hi there,

I recently brought a blackwater BW15 Carbine and have been told the rubber hopup needs replacing. can anyone point me in the right direction on how to do this myself. (Already have the new rubber)

Thanks!

MikeR

EDIT: After doing some test firing, the gun seems to be firing fine. No drop like my friend explained. However it is firing to the right of the sights. Is this common for airsoft guns? and if not how do I fix that?