Welcome to BYC. Glad you decided to join our flock. I'm sorry for the loss of your bird. It is almost certainly your Black Rock which is laying the huge eggs. Black Rock is one of several labels (other labels include Black Star, Bovans Nera, and Rock Red) under which some hatcheries market their Black Sex Links which are produced by crossing RIR roosters X Barred Rock hens. Black Sex Links are egg laying machines, outlaying either parent breed. It's one of the interesting quirks of hybridization. Not only do Black Sex Link hens consistently churn out more than 300 eggs per hen per year, but they typically lay very large eggs. Out of the dozens of breeds and hybrids that I have raised over the past 50 years, my Black Sex Links have not only been my best layers but they have laid my largest eggs with double yolks not being uncommon. Please feel free to ask any other questions you may have. We are here to help in any way we can. Good luck with your birds.