Did this expansion test several (10?) years back. Started with a 375 gr. .400 I cast in my custom Sching's adjustable mold shot in a White Shooting Star Sabot over 140grs. FFF ARCO Black Mag 3 out of my Hubbard's conversion .45 cal H&R Shikari.
At 50 yds. on a bench I lined up 6 one gallon milk jugs filled w/water, caps duct-taped on and laid a section of 4x4 across the tops to anchor things a little more.
Upon impact jugs 1-3 exploded, 4 & 5 were penetrated and torn, 6 merely dented, 4x4 flipped forward several yds.
Recovered the slug a couple yds. back uprange. Bullet retained nearly total wt. and expanded to virtually twice the original diameter.
Not sure what it may tell you, but thought I'd share it.
I've thought of rigging up a box with old leather, wet newsprint, water jugs, maybe dowels, etc. to simulate a 'realistic' target... haven't yet though.