The only question of ethics in this application is you making sure that you can cleanly kill the animal that you are shooting at. So assuming that you can cleanly kill the animal then go for it. It may not be for everyone but if you like this kind of thing then go for it.

IMO it matters little what caliber you use as far as ethics goes. Except for using a smaller than adequate cartridge.

Many people use rifles with larger bores than 50 and don't question their ethics.