Re: 338NM action??
Most folks are semi-familiar with nitriding barrels to:
Improve projectile velocity
Improve cold-bore accuracy
Reduce wear, time to clean, corrosion, and fingerprinting.
In this case (yours and others considering a BAT), you get all the "reduce..." benefits noted for barrels AND an even smoother operation (than for which BAT is famous).
If you were interested - though I suspect you are not - in a very high gloss finish (velvet-lined, English-style, presentation-case class finish), I've seen nitrided barreled actions that are truly magnificent. I, personally, go with matte black.
The downside for barrels is that you are pretty much locked into the length and current chambering - the surface is so hard that few gunsmiths will even consider TRYING to machine it. In the case of a BAT action, I'd be real hard pressed to think of a reason you'd ever want or need to cut on it.