Grotesque also have 2 wounds each, so they outnumber you much quicker than a normal squad would.
I put up the DE Player FAQ and I was questioned about this...
Q: Do Necron gauss weapons wound Grotesques on a 6 even though they’re not S6?
A: Yes, this is covered in the Necron Codex Gauss entry. Only on a 6 however, remove the model hit.
Q: Do sniper rifles wound Grotesques on a 4+ even though they’re not S6?
A: I'd say yes, per the BGB saying regardless of toughness. So, one shot one kill.
Apparently this is not true, per an earlier ruling when grotesque are injured in a raider crash.
They're taken from Chapter Approved pdf's downloaded in third edition but 4th edition shouldn't necessarily change anything seeing as the DE Dex is older.
Q When Grotesques (who need 6 STR to be wounded) take damage on a 4+ (e.g. their Raider crashing) do they:
a) Ignore the damage, as it isn’t STR 6
b) Take one wound, even though a 6 STR should auto-kill them
c) Die a fiery death
Models with multiple wounds are removed when the unit they are in has taken enough wounds to eliminate one whole model, regardless of whether the casualties were inflicted on different models. The owning player chooses which model falls casualty.
So, which one is it?