Thanks a lot Seth.
If you want references, please see Panzer Tracts 8 and 9, Sturmgeschütz IV by Marek Jaszczolt.
Funny thing - if we would have a late-war StuG IV on a Pz.Kpfw. IV Ausf. J chassis, then the Rundumfeuer ammo capacity would be 2,650 rounds. You can also e-mail Hilary Doyle for further details. Just PM, if you need more info.