From what I could determine - Challenger probably uses Cheddite hulls - so about any recipe calling for Cheddite hulls will work with the 28 gauge Challenger. I have never tried to reload Federal hulls.
I sold off most of my 28 gauge reloading stuff - since Nov. 2025, I have had about 2150 28 gauge Challenger 2 3/4" hulls on a WTB ad on CGN - no "sniffers" - maybe the shipping cost scares them off? I was asking $0.05 per hull. Maybe you can do better than I did.