I was looking at the TSX 300gr spitzers for loading in my 45-70 H&R single shot. I contacted Barnes via e-mail because I was concerned that they would not expand at levergun velocities (they are intended for 458WM and up). They replied with a minimum recommended muzzle velocity and the range that that would allow for reliable expansion. This was into Ruger No.1 load levels, which I don`t plan on using, so I deleted the response and can`t give you the specifics. Their No.1 starting loads for that bullet start at 2300FPS, but I seem to remember the recommended velocity as a bit higher though. I would drop them an E-mail detailing what you want to do, they are very helpful.
Jim