Need help on buffer size

[dickboxers]

So this is my first build.
I have DPMS lower built with a Magpul ACS stock. I am planning on a 22" or 24" inch barrel (rifle gas system).

I have been told conflicting things.

1. I need a rifle buffer spring and rifle buffer to match the rifle gas system. First question is I'm not sure the spring will fit in my ACS stock.

2. I have read people using the standard carbine spring and buffer for a 20" barrel (mid length gas system)

Can anyone tell me what the correct buffer system I should use with the rifle gas system on a 6.5 Grendel?

Thanks,