minnesotachickenbreeder,
What is hatch date on your birds?
Mine hatched late resulting in first set of adult feathers just now becoming complete. When they come into second adult set next year feathers the feathers should be a little bigger on tail and wings and muscle and bone development will be complete. Hopefully flight potential will then be improved.
As I recall ,the best flights were during cooler months outside of breeding season. Breeding birds, except for brooding hens tend to run heavier in the buttside which may reduce flight abilities.
secuono,
What motivates your birds to fly such distances?