For a tactical gun that will do most shooting at 100 yds or closer will a FF handgaurd rail make a big difference in accuracy (as opposed to a two piece handgaurd rail)?
Nope. Most folks won’t meet or outshoot the mechanical accuracy of the gun. Add now the economy ammo many are inclined to use that limits them even further. If anything, the FF limits the amount of influence they can exert on the barrel that might cause deviations.
Agree with Skintop. I don’t think you will see any change in accuracy out of a chrome lined barrel. What I like about FF rails is that they take pressure off the barrel.
I have seen people man handle a VG or sling to where the barrel is flexing and pulling rounds.
C4
I guess “tactical gun” means no match barrel, no match ammo, no match trigger, no match shooter 
, no match everything…
so to answer you question I’d say NO.
IMHO, a FF tube would be the final improvement I’m going to add to my rifle.
I’m also sure only a few people are able to notice (=to appreciate) the differences/benefits of a FF handguards (of course I’m not one of those 
)
just my .02$
This came up last week too. So I posted the link below then as well. It’s a thread with some good info on the FF subject if you feel like reading up on it.