This looks to be a 'runt egg', as I call them. I notice older hens who are done laying for the season, or during moult will often lay these smaller eggs. I dont think it is physically possible for a 10 week old bird to lay an egg, so whatever the situation you can snip that one from the list.
I know how to do it, and what I will end up with, the f1's will more than likely resemble a BR. My question isnt wether or not I should use them after breeding back to Black, my question was could a Black bird with leakage be used in the initial breeding of Black and Red. I ended up with a few birds that are very dark Red, which I believe will be my best breeders for this project. I know several breeders who sometimes end up with birds with leakage (normally a cull), but was thinking that the leakage wouldnt matter if crossing back to Red, as long as the bird came from a pure line of Blacks. Just wasnt sure the leakage wouldnt cause issues down the road a bit.
~Casey