NEMO Arms custom .300 Blackout Carbine Buffer Spring. NEMO Arms has engineered a custom carbine buffer spring for carbine length gas systems or troublesome .300 Blackouts that are undergassed. This spring was designed around a rifle with a 16″ barrel and a carbine gas system. This spring will also work with other This reduced stiffness buffer spring will allow your .300 Blackout to cycle properly with subsonic ammunition. The spring is made from 17-7 stainless steel that will not corrode and will keep its stiffness and tension longer than standard spring steel. **Please note that depending upon your gas port size, ammunition, barrel length, suppressor and other factors, you may have to adjust all of these to have your rifle cycle properly.