I run a Lothar Walther SS "gov't" profile on my 18" SPRish AR. It has the skinny barrel under the handguards. I got it from Scottmilk9, it is a 1:8 with a Wylde chamber and is way under the 2moa you're askin for.
I have the 16" version on my rifle and it shoots under 1 MOA </div></div>
they shoot OK, (I had the 18"WOA from ADCO)but <span style="text-decoration: line-through">LST66</span>LS6TT is asking about lightweight barrels, and the WOA SPR is an HBAR profile. The LW's Scott had made up (I don;t know if he still has them, but he could probably get them) were spun up to a coontour he specified, I think its .650 under the handguards.
Scott's still running Specialized Dynamics, but he's working on a new website.
The barrels he had Lothar Walther run for him were stainless 18" with rifle length gas sysytems. I don't have an exact pic or link, but imagine the top barrel in this pic I found online in stainless, 18" with a rifle length gas system, with whatever gasblock you want: