We had horrendous belly ache last night, which sent me on a mercy dash to the local store. I had been using avent bottles with the ring for my DD as well as the natural avent ones. I noticed yesterday while I was feeding her that she was sucking so hard on the teat that it had collapsed. I think this is the main reason for her bad tummy last night. Anyway I went and got Dr Brown bottles last night and I changed her formula to Aptimil comfort. I have noticed a big difference in her today. She has slept a few times today and has been less gassy. I really liked the avent bottles but I am not sure if they took enough air out of the milk for her. I changed the teat as well to the next one up, my DD is six weeks old, and I still don't think that the holes were big enough. She guzzles like you wouldn't believe but also gets frustrated if the milk doesn't come quickly enough, hence sucking harder and sucking in air. Now that I have changed the formula they definately aren't big enough and I woulld have to go to the next one. Anyway, I think it is trial and error. That is what I have found. We started with the tt closer to nature ones, like the dr browns, but imo they weren't very good. The rubber diaphram at the bottom split within a week of use and i think DD got more gas using them.
If you continue using the avent ones, tighten the bottle as usual and then just move it back a notch to make sure it isn't too tight. You need to make sure that it doesn't leak either, but as I said I think it is all trial and error. I also make sure i wind her after every 20 to 30 mls. She protests like you would not believe but it does seem to help. Hope this makes sense and helps in some fashion!