Bullet design and component materials has been vastly improved. Expansion has gotten much more reliable. New powders and blends have been developed to drive projectiles faster at lower pressures. Guns are also heat treated so better bullets can be used in them as metallurgy is now so far advanced. There are also many bullets designed for specific guns such as short barrel revolvers.

Most importantly, manufacturers now understand many things and manufacturing methods that were just not known 30 years ago. Records of actual shooting statistics have been kept, compiled, studied and dissected as to performance. Improvements are constantly being done.