All brass has been shot the same number of times, but only the cases shot with the 4895 have been splitting. The only variable appears to be powder, which is why I posted the question.

I have no idea whether faster powder is also hotter powder, but perhaps someone out there can comment. FWIW to achieve equal velocities (3700 fps with 55 grain slugs), I used 35 grains of the faster 4895 and 37 grains of Varget.