What buffer weight, spring to use for my .300?

[grey2112]

Hi guys - got my other parts for my build, but was wondering about buffer weight/size and spring options for my .300 project.

Using a CTR Magpul stock, billet lower, 16" and 10" uppers, almost exclusively subsonic ammo (though will occasionally go hyper) - mostly I'll be loading 220 SMK ammo at around 1000 fps.

So, what buffer (carbine or rifle), weight, and spring should I get for this application?

Thanks!