Basic Rule of Thumb with bismuth is that same VOLUME of shot as lead will give close to same chamber pressure and muzzle velocity, all else same. My own experience agrees with this, where P&V data from Tom Armburster was control. However, I only do this with lead loads having 1000 or more psi lower pressure than I am willing to accept -- this Rule of Thumb is NOT percise.
My perception of bismuth shot is that it is harder than even "magnum" lead shot. On waterfowl it performs like Cu-plated magnum shot, dragging few feathers into bird and therefore penetrating deeper. It also patterns tighter than even Cu-plated shot, even from long, cylinder-bore barrels. I use #6 and #5 for ducks and #5 and #3 (labeled #4) for geese. Have no need for better performing shot inside 40-45 yards.
My perception of TM shot is that it is rather soft, about as soft as "chilled" lead shot. In my guns, TM shot patterns more like "chilled" lead shot, giving distinctly lower % patterns than bismuth. TM shot also draws less feathers into birds. TM #5 shot kills big mallards nicely but often patterns too thinly for smaller ducks, especially teal. I have never seen any loading data for TM shot. I seldom use TM because almost all factory loads are heavier than I am willing to shoot in most of my old hammer doubles.
Niklas
