Quote History Quoted:
Not drop in, but Centurion C4 12 FSP uses a GI bbl nut and is kick ass.
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^This or the MI, I've had both, I prefer the Centurion well worth the coin, sold the rifle, which I regret, but I still have the MI on a Colt, love it, just as good, easy to install, and just as efficient as the C4, although I think the C4 is just slightly better, but not by much!