Maybe want a new barrel

[Koda]

For the sake of weight savings, I’m thinking about a new barrel 16” or 18” for my Grendel. I want good accuracy with the light weight. Should I go with fluted or just thin?

The lightest barrel is going to be pencil thin. Flutes don't really remove that much weight on a heavy barrel, but it can help a little on medium weight barrels which might be a good compromise.
What I would also consider is barrel temperature, thin barrels heat up the fastest affecting POI, in my experience at little as 3 shots (but that was with a hotter caliber)
Keep in mind flutes have a "net neutral" effect on barrel cooling, as the more material removed from a barrel the faster it heats up. IMO how fast a barrel heats up is more important than cooling since firing the gun is the critical moment of need. So then obviously with light thin barrels is they will heat up the fastest affecting POI sooner. This should be considered in a semi auto, especially if multiple shots are common like a group of hogs. On a positive note, pencil thin barrels cool down the fastest. Of course the accuracy (actually its precision) of a barrel is how the bore is made not the profile, but I'm uncertain how having a gas block attached affects barrel harmonics on thin barrels. Something to consider though and maybe someone can chime in on that.