Lew - this bullet was designed by Jim Cirillo, a former NYPD Detective, working in conjunction with Roscoe Stoker of RBCD. It was designed to completely fragment - basically disintegrate - in soft tissue targets.
I cannot speak to the why of each element of the design. I can tell you that according to published literature, the bullet for each individual caliber, while all of similar design, are formulated specifically for those calibers. The jacket is made of a “copper-rich” material made of five different metals. The jacket was designed to be ductile enough to fill the rifling of the gun barrel, and still to have controlled expansion to a point. It is claimed that the bullet jacket, because of its makeup, has 30 percent less friction than the gilding metal normally used for “copper” jackets.
The TFSP bullet, the only one available to the public, uses a soft-lead alloy pellet made of lead, aluminum, and zinc on top of a mixture of polymer and powdered metal. Its funny that published material talks about controlled expansion and then goes on to say that both of the two bullet types made disintegrate upon impact.
I cannot personally speak for the effectiveness of these bullets. Cirillo was an experienced gunman - in many gunfights in NY coming out on top, although wounded more than once, I believe. However, it seems to be another “wonder bullet.” I do not know, nor is it well explained, if at all, the function of the nylon filler at the bottom. That would seem to move the center of gravity of the bullet forward, wrong for accuracy in 9mm and many other pistol calibers, but to what self-defense end, I don’t know. Pinpoint accuracy is not always a necessary feature of self-defense handgun loads. They are not sniper rifles.
Cirillo developed other bullets as well, including a modification of the pin-grabber types, as well as a slotted tip wadcutter.
I wish I could speak more as to why the bullet is designed like it is, but I can’t. Cirillo passed away some years ago.
These bullets date from the 1990s and early 2000.
Reference: “RBCD’s New Sizzling Hot Platinum Plus Ammunition,” by Ed Sanow, “Handguns” magazine, April 2001, pp 36-41
Reference: “Performance Plus Super Stopping Bullets,” by Jim Cirillo, “Gun World” magazine, June 2002 issue, pp 57-61. Just my own opinion.
While I cannot speak for these two articles, neither of the above publications rates high with me for scholarly content.