Most of my boys are fine together, but my BCM chicks were even bloodier than yours; and it happened so quick! They were broody raised in the main coop and run with plenty of space to run and hide from each other, but the 3 boys were out for blood while mamma hen and the girl quietly ate at the feeder, ignoring the commotion. I even tried painting their heads with blue-kote; and it did not slow them down. I ended up puting them in separate cages for a week, and then I put all 3 together but in a place where they could see no ther chickens. They stopped fighting then, and I had CL take them away for me when she visited.
About 3 months ago my 2 Barnevelder boys got in a bloody fight, one tore the others comb. It did not last long, maybe a minute and it was over. I have 3 roosters in my main coop. A giant English Orpington (Serius Black) who is top roo. He had run out into the yard, and roo # 3 thought he could sneak in a little action with one of the hens while Serius was away. Well, Serius must have hired Duracell as his henchman, because Duracell sure went after Flop (Flop was a runt). Poor flop. He hasn't tried again that I have seen.