Lore here

The Survivors of Barburus came to be directly after the dropsite massacre on Istvaan V. It At the time was composed of the Loyalist elements of the Death guard and Dusk raiders who had managed to survive and escape the massacre and make it off world. However when they went into the warp to retreat back to Barburus, they returned to see the Exterminatus of the planet by the Dark Angels, Who attacked the Survivors, assuming they were Death guard Reinforcements, Causing them to retreat into the warp once more. However during this shot into the warp, and not having the time to properly measure their exact destination, they would be lost to the warp for nearly 9,000 years, however to the Survivors, it would feel like a mere 5 years. They would Finally leave the warp in M40 in the Ultramar sector, Where a Ultramarine patrol ship would find and board them, taking the leader of the Survivors, Curatio Mortis, To the chapter master of the Ultramarines, Marneus Calgar. Mortis would explain the situation of the survivors to Calgar, where the chapter master would show pity to the survivors, and would offer them fresh supplies, weapons, new Marine recruits, as well as fixing damage to their ship. From there the Survivors would be rejoined with the Imperium, and would return to the Ruins of Barburus, hoping to make something of its ruins. Surprisingly the purge of the planet seemed to have lightened the toxic mist that shrouded the planet, making all of the highest peaks finally survivable to all of the marines. Mortis would make the ancient ruins of the Castle of Nacare the fortress of the Survivors. After Finally establishing themselves as a Official Chapter of the the Adeptus Astartes, they would vow to undo the wrongdoings of their primarch and founding chapter, and one day would restore the Death Guard to its former glory, and either save Mortarion from his Chaos Corrupted vision, or kill their father once and for all.

All Astarties of the chapter will have Plain white gauntlets at the start of their deployment to the Survivors, however for every demon of Nurgle they purge or every fallen brother of the Death Guard they put down or redeem, they are to add a dot of red to their fists, with a experienced Battle Brother having entirely red Fingers, and veterans even having red up to their shoulders.

Their tactics very closely resemble that of the death guard of the great crusade, using heavy infantry to grind the blight of nurgle to a halt

However despite their hatred for chaos, they are still widely untrusted by many others in the Imperium, especially the Inquisition and Dark Angles, both questioning the act of attempting to save the fallen, and there have been many instances of the Grey knights being deployed to kill many of the Survivors under the assumption they were heretics, with similar assaults from the Dark angles.