I live in Arizona, the granite state! I have a two-compartment feeder on the ground with food in one half and oyster shells in the other. Even when confined to the pen, my birds have plenty of dirt, and various grades of granite/stones. I've never had any crop issues with my birds.Just to be clear, oyster shell is calcium used by the bird for egg shell production, while grit is small rocks, or stones, and is used by the birds for digestion.
That said, I don't supply grit, as my soil has plenty of small stones, but I keep oyster shell in a stainless steel dog bowl, screwed to a piece of 2x12, to keep it from tipping.
I had some sapphire gems, lovely birds! started laying at 18 weeks, which is the earliest range the hatchery and the seller of the parent stock says. Mine feathered and started to molt into adult plumage as early as 5 1/2 weeks, so I'm surprised yours are still molting into adult feathers at 14 weeks. I don't think there's any harm in offering the oyster shells as they're a free choice thing, you offer them in a separate bowl for the birds to eat when/if they choose.at what age do you start supplementing the calcium? my bag of oyster shells say 20 weeks but my friend says to start now @ 14 weeks. her father in law has raised chickens for many years... she has already started supplementing her girls. I have Sapphire Gems - supposedly start laying @ 15-18 weeks. But they are molting and it's not even 20 degrees outside... so I wasn't expecting anything until spring. Do I need to supplement them now?