I am defnintely not a buckeye expert, but I will tell you they do mature more like a jersey giant than a rock. They put a lot of the early weeks into bone and frame growth and muscles/feathers fill in later. You would do better to raise your buckeyes to about the 7-8 months range. This will help with the pin feathers too. Also, if you skin them rather than de-pluck you don't have to worry about the skin tearing.
Some breeders have made good progress towards faster growth but buckeyes are big and it takes time to get them there. The pullets do not lay for 6 months average. The good part of buckeyes is they can free range effectively reducing the months of pouring feed into them. Hatch in mid-late march and by July they will eat every mouse and bug on your property boosting their growth.