I played around with this a while back and what I found was that you actually need SOME weights that move in the buffer.
Without any weights, I had bolt-bounce problems in fast double taps.
Those moving weights are there to keep the carrier from bouncing off the back of the barrel extension.
JP uses an A2 buffer shell, but puts aluminum weights in it.
I have been taking A2 buffers and removing 3 of the steel weights.
Then I make a delrin spacer that accounts for the missing weights and the aluminum spacer that I remove.
This gives me a buffer that's slightly lighter than a standard carbine buffer, with just enough moving weights to eliminate the bolt-bounce issue.
For those not aware of what's inside your buffers, here's my buffer construction picture: