I just picked up a complete Knight's Armament RAS and it included the metal barrel block that fits on the lower front end of the assembly. However, I could not get the lower handguard past the delta ring with that piece in place. Am I installing it incorrectly? Is it optional? What function does it serve?

It seems like the two small springs on the metal barrel block might be for applying rearward pressure on the lower rail, so be sure you are pressing the lower handguard forward while trying to get the rear end past the FULLY pulled to the rear delta ring.  Once in place the pair I installed are rock solid.  One pair is on a Colt .gov profile rifle, the other on an FN barrel.

Supposedly the metal thingy is only for mounting an M203.  But if left out some lower rail play is present.  Good luck, try getting another set of hands involved.

Paladin

Thanks for the info.

Well, this is definitely going to take four hands...or the right tools. I simply cannot get the thing in place and I'm not convinced I have the slop in my rifle to use it. In fact, without the block, I can push and pull on the lower foregrip, and even with a vertical foregrip attached and I have zero movement. The whole system is way tight.

I'm curious though...what function does it serve with a m203 or anything else for that matter? BTW, I'm mounting on a Colt Gov't profile barrel.