My experience is definitely the Black Copper Marans. Out of 14 BCM eggs, right now I have 5 chicks. #6 was pipped for about 12 hours today, then a few minutes ago I noticed no movement of the beak inside the egg. Chick was dead, ...oh so close to have come out. Did not have the energy to zip. Do you all see this frequently??? Also Marans in general have shown the highest tendency to go breech, i.e. head at pointy end. At least with my dorked-up incubator, that has eggs on the side. My old incubator (TX-7) is officially being retired after this hatch. Welcome Brinsea!!! The TX-7 laid eggs on their side, and the circular wheel auto egg-turning motion never seemed to keep the pointy ends down all the time. So frustrating. So.... What breed chicken have you found the toughest to hatch?