There are generally two types of frangible handgun bullets. The sintered copper bullet is made with powdered copper with some Tin powder added as an adhesive. The mixture is pressed into a mold under high temperature and pressure. The other uses copper powder in a polymer matrix, but similarly manufactured. Obviously the manufacturing technology required is not nearly as simple as might be implied, and the current state of manufacture has been greatly refined over the past 30 or so years. When I first became involved back in the mid-1990s, there were many problems to be overcome, accuracy performance being a big one. Regarding frangible bullet breakup on a leather jacket, that is highly doubtful, if not laughable, but anyone anticipating using frangible for defensive purposes is advised to perform some simple penetration testing on various materials beforehand - leather, denim, wood, books, glass, etc. Also, different makes, diameters, velocities, and weights of frangible bullets are likely to perform differently in penetration of common materials. As previously stated, frangible bullets were not designed nor intended for defensive use but rather to break up on impact with hard surfaces, so you are on your own for "off label" use.