Could I make a fireforming barrel out of a barrel with the wrong bore diameter?

Here's the scenario, I have a 338 bore barrel that has proven to be pretty worthless. I've tried different chamberings, new crown, different actions, stocks, you name it. This sucker is a tomato stake! In the next couple of days I should be getting my 375 RUM Improved reamer. Could I rechamber my 338 bore barrel with the 375 reamer to use as a fireforming barrel when shooting Cream of Wheat fireforming loads. Obviously it wouldn't work to fire bullets, but with the COW method, I can't think of any real harm that could come from doing this.

What do you think?

Andrew