Lead, What fps does it deform?

At what velocity threshold does pure Pb deform into the mushroom? For example, using a BruceB soft point in a rifle or low velocity handgun cartridges like the 38 spec, 380, 44 spec, 45 ACP, suggesting velocities are between 600 to 900 fps. The medium of impact would be something like the double lung shot on a deer, just hair, a little meat and green rib, and soft airy lung tissue, not talking of hitting dense muscle and bone of the shoulder. Another impact criteria to think about would be if something like the 38 or 44 spec started out @ 750 fps and traveled 25 yds it might be doing less than 700 fps at impact. So, as it traversed through the medium stated above velocity would dwindle quite a bit unless something like the heavier 44 cast boolit was used instead of the 158 gr. Would this lack or diminished speed hinder total mushrooming half way through the medium even with the pure Pb? Try not to use water jugs, ballistics gel, or wet newspaper for the thought process.

Attachment 237223 this is the only pure lead bullet ive got from a deer. Its a 250gr truncated cone cast of certified pure at aprox 1300fps impact vel from a muzzleloader, i was a lengthwise shot entering windpipe. Mushroom velocity will change based on shape, a truncated cone or rnfp shape will have more resistance to expanding than something like a keith shape with less "beef" behind the meplat. shots on a deer is very hard to say as its not a consistant medium, sort of like asking will a bullet go through a car, sure it could but will it hit a part of the door frame, or an electric motor etc. Who knows. Me id probably just go soft cast hp if i wanted expansion under 1k fps.