Same here, but crush them pretty small(1/8-1/4") in DIY mortar/pestle(metal one cup measure and a heavy water glass).I rinse and dry them on my counter and put them in a gallon baggie, crushing them once they are in the bag.
I mix them in with the OS.
Egg shell alone isn't the best calcium supplement, moves right thru them,
where as the OS stays in the gizzard much longer.