Cool I may just check this out then. For hardcore is there a certain class set up I should be using? Or anything I should definitely not use?
Perhaps the most useful class for the Attacking team is Recon because they get spawn beacons, letting you and your squad members get closer to the MCOMs without having to run all the way from the spawn area. This is a great way to stay on top of your tickets and keep momentum moving forward. A recon with a Carbine, DMR or Shotgun is as effective as any other player.
But really all classes are important. Of course you need Medics to revive and heal, Support to resupply and use things like the XM25 or Mortar to clear out defenders camping an MCOM. Engineers are useful too as in hardcore vehicles don't regenerate health and of course vehicles can be a real asset when used correctly. I've also seen Engineers use the EOD robot to arm/defuse MCOMs remotely.
Smoke grenades can be a really big deal, especially in hardcore as you don't have a minimap. Either setting the charge or defusing an MCOM is much easier when the enemy team can't see you in a cloud of smoke. They can also be used to just block sightlines, so if you have a sniper or a machinegunner on the enemy team covering a route you can use smoke to get past them. From a defensive point of view, you can also exploit the urgency of the attackers by using smoke at the entrance to a position. The attackers will charge in blind and won't see prepared defenders until it's too late.
As for what NOT to use, claymores can be a real pain in the ass because both you and your team mates can trigger them so it's a sure way to get friendly fire kills. The same goes for anti tank mines. In hardcore you don't really need a suppressor on your weapon since there's no minimap, so feel free to use a better attachment in that slot. Everything else is good really.
I play on PS4 and there's a few servers set up for hardcore rush that have really good maps. Many of the expansion maps are far better suited for Rush than vanilla maps.