Go to Airsoftparts.ca
Jugglez (ASC name) runs it and is top notch.
You'll find a ton of tightbores and stuff under the AEG Internals section
http://www.airsoftparts.ca/store2/in...ed52ef8a40877f
While you don't technically need to do anything but swap the inner barrel out...you may want to consider swapping the hopup unit and hopup rubber at the same time.