Don't add any lead to your fly! You want to keep the fly as slim as possible. I would also use white antron for the gill. It stays brilliantly white when wet and doesn't add bouyancy as CDC does. I usually use a very small split shot about 12" above the chironomid to get it down. I believe it also allows the fly to kind of pendulum under the split shot for some very minute, but lifelike motion to the fly. Here is a link to my favorite chironomid pattern: http://shop.flyfishing.about.com/fly...etails/248.htm
I have since alterred the pattern somewhat. I now use whatever colour thread I wish the body to be, as an underwrap and then build the body with clear v-rib. This gives a more translucent look to the fly. You could also use small liquid lace in place of the v-rib.