For typical AR15 rifles with 16" or longer barrels and a fixed-stock with a full-length, fixed-stock buffer tube, we recommend the RB5001 rifle buffer with a JP .223 rifle buffer spring (part no. JPS-OSR).  This combination works well with .223/5.56mm guns as well as many other AR15 calibers in this configuration, such as .223 Valkyrie, .350 Legend, .450 Bushmaster, 6.8 SPC, 6.5 Grendel, and many more.  

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