My gas piston system's gas block was a flat top. I took a tape measure and held the end on the barrel and measured how tall the gas block rail was. I then measured the old front sight post gas block from the top of the hole where the barrel went through. The difference was 1.5 inches. And Yankee Hill makes one, flip up, and it was in stock at a local gun store.

So...I would say if you have another or go to a store and measure the factory front sight and see how tall you need it to be. Of course it may depend on your rear sight. If you get a carry handle type rear sight this works great. However, I don't know beans about optic rear sights in relation to the front sight hight.

My gun's zero was dead on. Didn't have to change sight settings.

I GOT TO GET ME SOME "MAGPUL MOE's"...coolness factor.

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Army.USMC.Airforce (Res)