For what you'd be taking off the barrel it would be hard to imagine any part of the bore growing. Plus the fact you're taking it off directly over the chamber so in the end the size reduction shouldn't matter much.
What I did recently as an experiment was put a 30-06 Remington take-off between centers, turn the shank down to approx 1.120" and then thread for the Savage large shank barrel nut (final thread was a tad undersize at 1.112 x 20 tpi but still within 3A thread classification). The barrel nut fits over the original Remington threads and allows someone a much cheaper option than spending $65 on a Pac-Nor barrel nut. Admittedly the threads aren't exactly the same but in the end it doesn't really matter and still accomplishes the goal. It worked out pretty well I would say. I'm just a beginning lathe operator though so the threads aren't 100% perfect but I was very happy with the result. As a word of caution...the Savage "blue" barrel nut isn't blue, it's gray. If I were to do this for myself I'd just use the regular barrel nut in stainless but that's just me.