The 33 was a small frame rolling block made for relatively small cartridges. Made for shooting Capercalle (sp?) out of trees around the turn of the century. Small rounded frame and not slab sided like the military models.
The 9.5x47r and similar rounds with a 28ga being the largest shotgun round that would fit that frame. I have also seen them in 24 and 410.
My guess is that I could easily build a 32-40 or 38-55 in the 6# range if I wanted to. I do know someone who had the original tapered octogon rebored to 40-65 but it always seemed to be a bit much as there wasn't too much metal left where the barrel was threaded into the reciever.

Did find this web site with pix and some info.

http://www.skydevaaben.com/husqvarna/model33/info.xml