What would the grav weapons space marines are getting do?

Ive been reseraching lately and multiple sites are saying that thell lower I or pinning some of my units. The Centurions the SM are getting have these and man oh man im kinda worried if theyll be our anti infantry nightmare.
I know thell be T5 and thats no problem but 2+ saves with 2 each they are paladins lolz
Anyways leave some comments. Just want to know for sure what rumors are true.

First thing: the codex is not out yet so any answer will be purely speculation. I've heard that it wounds against armour save instead of toughness.

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Just want to know for sure what rumors are true.

Things that you'll be hearing will be rumour. You cannot ensure a rumour is true by comparing it with other rumours. Just wait until the codex is released and that should help.

Any update on this now codex is out?

There's plenty of information out there now about grav weapons. Essentially they wound against your armour save rather than your toughness, they are AP2 and against vehicles they cause an immobilised result on a roll of a 6 in lieu of the normal armour penetration/damage roll.

+1 to Adhemar, also remember they are salvo 2/3 at 18", or salvo 3/5 for heavy at 24". The heavy version only comes on the centurions that come with a grav amp, which allows them to re-roll to wound. Also reminder centurions are relentless, so they will always be shooting the 5 shots