I would sure not think of PP, 2400, or even Unique as being "indoor" powders.
They'll sure make noise! BE, OTOH, can be a lot of fun. You needn't vary the charge very much, as you're loading it for close practice.
With the RNFT, it won't mean much, but if you used a Keith-type SWC, you could seat the bullet deeper, say 'til the front of the shoulder is even with the front of the case. It would then be about the same OAL as the Special, and have the same internal dimensions. Doing that, you wouldn't have the problem of a ring of lead at the end of the chamber, as you would using a Special case.
You needn't worry about BE giving dangerous pressures as you're working with Spl loads. You might drop it back a little, if you like. I've shot a bunch with 5.0gr, so you might start at 4.5 and go back up.
If you can get near a chronograph, you might run a few through, to see exactly where you are.
Have fun,
Gene