Bring your sig 516 from 2010 to 2014 - Midwest Industries SIG 516 Extended Free Float M-LOK Handguard

Having suffered with the stock picatinny rail and the trial and error of the lancer carbon handguard this is pretty much the only handguard to get for your sig516 should you choose to continue using this abandoned firearm platform.
Funny enough the lancer full length actually weighs more than the picatinny version.
So you're stuck with a short rail probably the lightest one for this platform that actually makes it feel like a modern AR instead of a big clunky mess the lockup method not confidence inspiring but gets the job done. There's no heat shielding so you'll want to get some rail covers as far as mounting lights and everything I definitely have a gripe with the forced use of a QD cup on the end of the handguard where I would want to mount a light as far forward as I could.
The finish is not as robust as the Sig sauers on the receiver but once you attach some accessories rattle can this thing you'll never notice.

It's either this or go the custom route like some guy on AR15.com did by changing out the barrel nut with a GI and doing some trimming to make a Centurion rail work.