Sorry if this is a noob question but what are these two tabs that are inside of a RIS II rail? This is a non FSB rail and the pic is of the muzzle end.
Thanks!
https://danieldefense.com/rail-systems/ris-ii/m4a1-rail-interface-system-ris-ii.html
The Daniel Defense Rail Interface System (RIS II) was designed at the request of the United States Special Operations Command (SOCOM) for the SOPMOD II program. SOCOM had a specific requirement for a free float M203 solution and Daniel Defense responded, designing a revolutionary product to meet the government’s need. The Daniel Defense RIS II allows the individual operator to free float the M203 grenade launcher without additional parts. As importantly, special tools are not required to mount the M203 grenade launcher. This was accomplished by integrating all of the needed parts to free float the M203 into the rail itself. The Daniel Defense RIS II is to be used in conjunction with the MK12 Low Profile Gas Block.
The Daniel Defense RIS II free-floating Picatinny rail systems are designed to allow individual operator to quickly, and without special tools, mount M203 Grenade Launcher and precisely mount SOPMOD accessories to host weapon without effecting point of impact. The Daniel Defense RIS II is an innovative upgrade to the M4 platform and is available for commercial purchase directly from Daniel Defense or any authorized distributor.
So in short, this is for the M203. I’m pretty sure I won’t be utilizing this. 
Thanks for the reply.
Yes. And DD should simply make a run for civilian sales and omit those.
Yup. Take 'em out. They shoot loose and rattle, then you have to take the rail off to get 'em out later.