The product you're looking for is ICS MA-12 - thats the S.I.R
http://www.wgcshop.com/wgc2008/main/...no1=&orderno2=
http://mach1airsoft.com/site/node/386
You'll want to avoid the ABS Plastic ones if you can, but if price is involved do what you gotta do.
I've seen people with plastic ones break them in pieces when putting a foregrip on and running around. They're not very sturdy unless you're very very careful with them.
Dboys CASV is similar and can be used with your delta ring:
http://airsoftdepot.ca/catalog/produ...roducts_id=812
Might find something interesting in this thread:
http://www.airsoftcanada.com/showthread.php?t=7204