See this link.... David Tubb has won the National High Power championship about a zillion time.
I use his springs and CWS (carrier weight system) in my 20" Service Rifle. It works great. There is also a system and springs for carbines. There have been a ton of threads about "heavy buffers". This is essentially the same thing, only the weight is in the carrier, not the buffer. During recoil they move together. It's the "timing" of the beginning of the travel of the bolt and carrier that gives the impression of less recoil, it comes over a longer period of time.
It allegedly helps with some extraction problems as well, but I can't comment on this from personal experience as I wasn't experiencing extraction problems before using it.
By the way (or should that be "weigh", lol)... he's got lots of other products on his website. But here's the link to the CWS page.
David Tubbs CWSIf you're interested in the high end of AR performance, and you don't need to be a High Power competitor to appreciate some of this stuff, check out Glenn Zediker's site:
Glenn Zediker's AR site he literally "wrote the book" on getting the most out of AR accuracy.