Update:
Took Kos-Mos's advice and picked up a couple of Modify springs. The difference from the JG springs is like night and day. With the Modify S90+ spring and some tinkering the PDW shoots 95m/s or ~312ft/s at 15 rps.
And here it is with happy new spring
I haven't tried the S110+ spring yet, gonna have the S90 a whirl at a game this weekend.