I may be the sole voice of dissension.. but I ran a standard weight Buffer for well over 12 years in a 16" HBAR Carbine with well over 14K and never had a problem or felt the need to change to a heavier buffer. Heres what it looks like.
http://img.photobucket.com/albums/v4...4/IMG_1212.jpg
When I finally picked up a new Upper and lower it came with a H buffer. To be honest. After a few hundred rds... I can not tell any difference. and because I switched from a 16" HBAR to a 14.5" M4 profile.. The muzzle jump and recoil feel a little more severe due to the loss of the extra barrel weight I'm sure.
So, I can't say as I'm sold on the heavier buffers for the 16" and 14.5" carbines. I know the shorter SBRS seem to run better with them. Just my take on it.