Thats a whole lot of cartridge for a 20" barrel, kinda defeats the purpose of the 28 nosler. I dont think many guys are running them shorter than 24", myself included.
I'm shooting a 28" barrel on my 28. If barrel length was a concern I would choose a less overbore cartridge. The 28 thrives with RL33 and N570, and those slow powders need room to breathe.