The beakies are in Corvus armour – the obvious name GW gave them because corvus-corax is basically the Latin name for the common crow, hence the Primarch of the Raven Guard being given that same name.
In 40K the marines mostly wear Mk VII armour with the Darth Vader style shouting mouth grills, and pieces of the rarer Mk VI Corvus armour. Unlike Mk VII armour, Mk VI armour doesn’t have shoulder pad trimes; they have studs on one shoulder pad; no knee pads but knee high greaves; a Rogue Trader marine style backpack with the ridges at the top of the middle section and several triangular shapes beneath it; the chest plate has three cables in a Y shape; and last but not least, the eponymous beaky helmet (which was said to house extra sensory tech’ etc which made them and the whole suit in general, the most advanced suit of armour at the time of the Heresy, after MK IV armour).
Some of the early Jes Goodwin Mk VI marines also had ridges on their boots, which GW sculpts onto Mk VI marines from time to time (to me it completes the look of a full Mk VI suit).

These FW illustrations of the Carcharodons are wearing Mk VI, Mk VII and the ad-hoc Mk V legs with the cables on the thighs and Dalek-like studs on the greaves. The studs are meant to be “monomolecular bonding studs” (I think that’s what they called them, lol) that allowed the marines to fit armour plates together when repairing them; hence the exposed cabling on the thighs showing that they are hasty battlefield repairs or refits.

From the look of the blood splattered FW painted Carcharodons, I thought they were related to the World Eaters, especially when one of their characters has two chain blades set into their power fists! They don’t sound like Raven Guard either, apart from that “strike and fade” style tactic AJ described. Maybe they’re a combination of the two gene-seeds?
Perhaps experiments were made to use what gene-seed they had from the traitor legions to create extra Second Founding chapters, and when they found them to be a bit too extreme, they, like the Carcharodons, were sent far away to look after the outer rims of the galaxy.

While I feel them to be more related to Angron, I will say that in the Horus Heresy after Istvaan V, the Raven Guard tried to replenish their numbers by accelerating the process of space marine creation, which in turn created mutant marines who had raven-like claws, talons, scaly skin etc, and I think in some cases, black eyes – which is not unlike AJ’s description of the Carcharodons. The sharpening of the teeth still sounds like the World Eaters to me though, so I dunno…

I wish GW/FW wasn’t so vague at times lol!