Okay, so i found a fired and sized Hornady .358 Win case, stuck a spent primer in it, and got:
163.9gr empty
57.9gr water capacity
That puts your case capacity at 98.3% of mine, and as mine has been fired and resized, i would basically consider there to be no practical difference in case internal volume.
Now, while, as i said, ive never used 3031, i will say that, in my loading experience with H4895, i have run charges up to 48.0gr with 200gr Hornady FTX, and 100% case fill comes somewhere around 46...so theres a bit of crunching can be done pretty safely in most cases. Though ive never had it fill all the way to the case mouth.
Btw, a look in my Hornady load book puts max charge of IMR 3031 with their own 180gr SP w/ 2.600" OAL at 46.8gr.
Not sure what the big discrepancy is about. Maybe lot to lot consistency with 3031 hasnt always been great?