Crunch,
I'm sure you might have come across this one already, but here's a great write-up (hopup part is way down in the review) in case you haven't.
http://www.arniesairsoft.co.uk/revie.../cat/16/page/1
In case the link doesn't work, it's in the review database of
www.Arniesairsoft.co.uk
Best of luck!