ASPUK do an advanced hop arm which is meant for heavier ammo, I may even have a spare one I can send you.
Unfortunately my l96 is the TM l96 aws, thanks for the offer Hef, but that arm wouldn't fit I am going to try out a new hop rubber and the packing fix off the sniper forums
check this: http://www.airsoftsniperforum.com/44-others/2398-tm-l96aws-detailed-hop-up-spacer-fix.html