Well considering if it is even possible for a Viper Tech to use WE mags considering they use completely different systems there is no way to get the bolt catch to work unless you get different mags as the way a we tech mag engages the bolt catch is different from how the magma/western arms style mags engage the bolt. So your only options are to get new mags that uses the western arms/ magma style which are Beta Project, Prowin, G&P, GHK(best mags out of all of them), eb tech, JG, and Kingarms.
Also an npas is a valve in the bolt that allows you to adjust your fps by a turn of a tool