In the Colt system the 9mm heavy buffer was designed and implemented for a good reason. The extra mass slows down the cyclic rate, which is directly related to reliability, and especially the longevity of your components. Heavier is better.
If you are looking for a lower you can quick change between calibers and not worry about buffers.....run a 9mm buffer in everything. I have been running a 9mm buffer in my 223 for almost a decade.