actually I started making a BA chart for this using user-reported equivalencies. Most people seem to find snorting about equal to plugging, and oral lower (in terms of BA) If you look at the molecule, it has many similarities to the -morphones which means that I would expect oral BA to be somewhere around 30-40%, snorted/ plugged around 50% and IV (obviously) 100%.
The data I have seems to support this.
IT seems to be about 3-4x weaker than morphine, so maybe 2-3x weaker than HC, so I would try 50mg and work up. You can always take more, but never any less.