http://www.airsoftretreat.com/review...hp?product=191
I found the hardest part is trying to slide the barrel and hopup sleeve into the chamber without stretching the sleeve. I used some silicone oil to help slide it in. Be careful not to force it or you'll tear the sleeve. Also use your finger to feel and match the groove you see on the sleeve to the grove in the barrel. Make sure it is in the groove.