https://lmtdefense.com/product/full-auto-enhanced-5-56-bcg/
the e carrier will have 3 holes where as the standard will have 2,also the bolt itself is different in that it has two springs utilized on the extract hence the odd shape.
over all lots of improvements tailored more to the FA crowd.
SLR solo light weight series meets your criteria,the 15" comes in at 10.7oz.
this is listed on another board
https://www.m4carbine.net/showthread.php?230703-SLR-SOLO-Ultra-Lite-15-quot-556-Handguard