Meatgrinder

While Imperial records show that only the Word Bearer legion retained the station of Chaplains in their ranks, the Iron Warriors maintain an outgrowth of this sect as well. Rarely seen beyond the hellish daemon world of Medrengard, the chaplains of the Iron Warriors no longer preach to the warbands of their comrades; such cold-blooded, single-minded slaughterers no longer have need of spiritual guidance to know their place in the cosmos. Instead, the Chaplains corral those slave shock-troops who have decided that a swift death on the battlefield beneath an Iron Warrior banner is better than an eternity slaving in the bottomless factories of the prison planet. In every battle, untold thousands are slaughtered, wave after wave, only to tire the enemy and run down their munitions before the real strike teams make their assault. Such canon fodder are not even referred to as human, designated only as "flesh."
If any of this "flesh" survives more than a handful of battles, however, it is the duty of the Chaplains to evaluate the survivors to determine if their longevity is mere luck, or a sign that they are made of sterner stuff. In the case of the latter, the Chaplains begin the long and grueling process of grooming the individual to become a new soldier in the Iron Legion. The trials of this process are horrific and arbitrary, such as a lottery of ritual decimation by beating, a tribute to the first order of the Legion's demon-king, Perturabo, upon seizing his command. Only a fraction of would-be Iron Warriors manage to survive their initiation rites, having suffered through constant battles, crippling injuries, and meaningless victories, all without a single word of recognition. It is at this point, utterly broken, paranoid, and embittered, that the Chaplain offers his most important service of all. One-by-one, the chaplain recounts the names and battles won by every initiate, every wound they had received, every enemy slain, and every bullet fired. He marks their victories, forgives them all transgressions, and offering them their power armor, for they have truly proven that they have iron within, and have earned the iron without. As Horus had praised Perturabo in his darkest hour, so the Chaplain praises his Neophytes, and though it is the only kindness they will ever receive, it is enough to bind them to the Legion forever.

Due to the nature of their duties, segregating the flesh from the iron, the Chaplains have always been dubbed the "Meatgrinders," reclaiming the old insult thrown by their enemies as a badge of pride. Their Chaplain skull-masks are designed to mimic the iron skull of the Legion badge. The Meatgrinders as a whole were very put out by the Daemonculaba debacle, which they considered an affront to both their authority and the traditions of the Iron Warriors. Their sect has not yet forgiven Honsou's transgressions, but have not yet decided upon a Warsmith they deem worthy to replace him.

This is all just crap I made up. Still, seemed to make sense, what with the Iron Warrior's battle tactics and mindset. Love the two patchwork Neophytes in the background, with their shitty, cobbled-together armor taken from Pyrrhic victories against other camps, Imperial scouting parties, and wasteland barbarians.