Yeah in my mind it’d be a “blank-only” gun, a movie prop. Which is well within the budget for movies like this, I mean they have a dedicated armorer. Resizing a barrel isn’t uncommon, based on Wikipedia searches, so while it might be a hassle, it could definitely be done within a reasonable timeframe and cost, and avoid any mechanical issues with the gun, but would be pretty high on the list of things a movie would cut corners on if it decided to.
Which is what I gather happened here, anyway, so maybe this IS standard practice.