First I gotta say that I thought I was pretty good at searches but this site absolutely ninjas my search skills. That and the one search per minute, no results older than 30 days limit is murder.

OK, got that out of the way.

I've got an AR-15 HBAR that I want to start shooting in service rifle class.  I know that if I stick with it long enough I'll go to White Oak for an upper, but until then I'd like to know what I can do to free float the foreend and get the sling off of the barrel and stay service rifle legal.  

you need something like this:
http://www.brownells.com/.aspx/pid=9943/Product/AR_15_NM_FREE_FLOAT_BARREL_SLEEVE

i just happen to have one i'm trying to unload - PM me if you're interested.

The sling is required on all stages in Service Rifle, whether you use it or not
Bye

The point isn't to get rid of the sling, it's to move it off of the barrel and onto the floating forgrip so the pressure doesn't effect the point of impact.

Armalite, BM, CLE, DPMS, Fulton, RRA, Young and others I'm sure.
High Power Forum may know of more