After building and using about 15 different .308 platforms I came to the conclusion that even Slash's carbine .308 heavy buffers are a band aid and will never run as well as a rifle length extension set up. If the carbine extension is a must then a CAR-10 XH buffer with a Sprinco orange spring has proven to be the best choice for me. I saw 0 difference between a A5 with a XH buffer (A5 extensions can use a standard AR15 length buffer even with .308's) with one of Slash's springs and the standard AR15 tube with a Sprinco orange spring. Also I am not a fan of the springs he sells. When I see surface rust on a spring less than a month old I tend to suspect the quality of the spring immediately.