Hi BB,

tried the 75mm, 5.3 x 3.8mm port gun with a 3.2 port instead.

3.8 port 8.4s: 768, 7.9s: 796 (so slight bounce)
3.2 port 8.4s: 722, 7.9s: 760 (lots more bounce and lots less power)

I then removed port and reassembled and it came back (withing a couple of fps) to the original/ Consistency was +-5fps throughout.

Empirically this is as expected, as when I see bounce, reducing the port can only reduce power/increase bounce. For shrinking the port to help, I'd have had to have seen slam - all in my experience anyways....

By way of more data I then added a 2mm preload spacer (wanting to get rid of the little bounce, plus a little spring guide grease ) and got:
790/813 (bit close - shows how easy this thing can make power though - looks like that washer needs to come back out)

Dave, preload is around 40mm, wire is 3.2, OD 20.6, forgot to count coils but it's a pretty "average" pitch around 8mm. Will measure it when I remove that washer !

Rgds - JB