IMO you don't need to install one. The bolt is bigger & heavier on 308AR. It slams back to battery with authority every time. I know at least that the SR-25 does not even incorporate a facility for an FA, at least the older ones don't but I don't know about new ones. And besides that the bolt carrier I have does not have any serrations for a FA anyhow. What I did. I went to hardware store and bought a black chrome bolt cover thingy. The kind that a custom car guy would utilize under the hood of his bitchen car. I found one that fits inside FA hole perfectly, I think it's 1/2" diameter? I used red loctite to make it stick. Looks great!!