Standard Power Rifle Length Buffer Spring.The Green spring is for use in A1 / A2 fixed stock rifle length receiver extensions (buffer tubes) with rifle length buffers. It is also extremely popular in intermediate depth (7.75 " deep) VLTOR A5 buffer tubes with 4" A5 buffers. The spring design loads of the Green spring are those of a BRAND NEW mil-spec buffer spring. While the Green spring is primarily for use with lesser calibers such as .223, 5.56. 6.8 SPC, 6.5 Grendel, 7.62 X 39, etc. in A2 rifle length tubes, it may sometimes be appropriate for use in long BBL (20"+) rifle length gas BBL's in heavier calibers such as .308 and 6.5 CM, .260 Rem, etc.. (May not be e Mfg: Sprinco Usa