I've got a set of MI 2-piece rails, and while the top portion is absolutely solid, the bottom section section started solid, and has progressively become more and more rattly. My friend has a set of YHM 2-piece rails, with a similar condition. What we've both noticed/inferred, though, is that it's not the handguards' fault, but rather, the fault of the handguard caps, which tend to bend forward, under pressure.

While the bending seems to be limited by the allowances in the barrel nut capture groove in the handguards, it's still enough to cause noticeable rattle with a VFG under pressure. My interim solution's been to use aluminum foil to shim the insides of the cap, but it's not an elegant solution, and I have to keep replacing the foil, as it's not very durable. Bending the caps backwards is also only a temporary solution.

I'm wondering if any of the 2-piece manufacturers have at any time considered offering thicker/stiffer stamped, or otherwise machined handguard caps. I, for one, would be interested in having extra stability.

I've noticed this too, my MI rails wiggle if the upper they are on has a loose handguard cap.  (I just got a new/different upper).  Otherwise they are rock solid.

Quoted: IMHO making a more rigid handguard cap will only hurt accuracy.

Reckon? By my figuring, the rattly configuration isn't exactly loosely-coupled in comparison. If anything, I'd expect better precision with the dampened barrel harmonics. But for my sort of shooting, having a rigid setup is more valuable than super accuracy.

I had a bit of a wiggle problem with my MI Carbine Length rails a while back.  It talked to the always helpful folks at MI and they suggested that my handguard cap was just slightly out of round.  Turns out they were right. I ended up taking a C-clamp and squeezing the cap at the 12 & 6 o'clock positions untill I'd bent thing back into place.  W/ the cap tight on the top and bottom sections they lock together rock solid.

h.gif

Get a couple of long black tie wraps. One on each end will do the trick.