Not sure what you think "steel" is a singular hard thing, it isn't.Not sure why we think that a softer metal like bronze will hurt a harder metal like steel. All you’re doing is wearing down the bronze bristles prematurely.
In the case of a revolver, I would get a short brush. Overall, I'm not afraid of Phosphor bronze in any case. It has aIs a Phosphor Bronze brush to be pushed completely thru before reversing or is it okay to reverse before while in the bore?