I had the same issue with sooting using the Hornady 90 grain SWC and 2.3/231. It is annoying but doesn't really hurt anything; I would guess you might try seating a little deeper to increase pressure a bit.
After using up the SWC's, I tried some of their HBWC with 2.0/Bullseye, which is the max recommended for that bullet in the Hornady manual. Seating depth is flush (.920") and a slight roll crimp is applied over the bullet shoulder. The sooting stopped and this is an accurate load, so much so that I think this is the bullet I will stick with from now on. Considering the small size and light weight of the HE I use it in and the knife edge front sight (with corresponding slim topstrap groove), I typically very seldom shoot at anything past 50 or 60 feet. The WC doesn't give up anything to another style of bullet under these circumstances. I would expect it would lose stability at longer ranges.
I think .32 Long data is kept pretty conservative owing to all of the old guns out there. I believe there is some latitude in stepping it up in improved I-frames and J-frames by the careful handloader but I am not inclined to look into it (at least not at the present).
I have recently seen a Model 31 in 2" in a pawn shop....maybe I have an excuse for another gun to experiment with
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