The Rugers are a stronger platform, no doubt, but that's not to say that a Handi won't handle modern rifle/Ruger loads, specially when some data shows levergun data that's still in SAAMI trapdoor pressure of 28kpsi! The Handi will be just fine, but the shooter is the weaker link when you get into levergun loads and above, the recoil is just tremendous, most stay in trapdoor/lower levergun data. The 500S&W is factory chambered in the Handi, it has a bigger case head(.525" vs .505") and a much higher SAAMI MAP of 60kpsi, although top load data peaks at around 53kpsi, so 50kpsi/kcup loads(Hodgdon and Hornady) in a 45-70 aren't going to be a problem for the gun, just the fella behind it. The only 2400 load I've used is 28gr under a 350gr Hornady(45-70 Loadbook Alliant data, 27-29gr) for about 1500fps, very accurate.
Tim