but how the heck do you install the thing on a fixed front site (M4 type) carbine?

I understand that one is supposed to remove the FSB from the barrel in order to slide on a standard free float tube, like the Larue, KAC, or DD seven-inch units, but how does one get the FSB to stick up through that opening in the top rail of the 12-inch carbine unit?

It's a neat looking rig, but a bit more money than the standard 7.
I like the idea of "more real estate" (today, at least!), but am a bit confused about assembly.

I've never done it but it looks like you slide them both on the barrel together. The forend looks like it has cutouts on the side to install the taper pins.

Maybe that's it!

Looking at the photo available at the DD website, those holes do seem to be in about the right positions.

Cool . . . . .

Thanks for the info, y'all.
I feel kind of unobservant right now.