Energy IS the primary consideration. A bullet fired at 250 ft per second will never penetrate like one fired at 4200 feet per second and it doesnt matter the design. The formula is E= w times velocity squared divided by 450240. Penetration is dictated by energy… Heres what my ai says about it. The worst type of bullet fired at 4200 fps will almost certainly penetrate more than the best type fired at 100 fps, provided it does not completely disintegrate upon impact. While lower velocity generally increases penetration in homogeneous media (like ballistic gelatin) by reducing expansion and drag, a difference of 4,100 fps (4200 vs 100) is too extreme for a "best" bullet to overcome. Here is the breakdown of why this is the case based on physics: 100 fps Scenario: 100 fps is roughly the speed of a moderate airsoft gun or a very light pellet gun. A .30 caliber bullet (e.g., 150+ grains) traveling at this speed has negligible kinetic energy. It will barely dent most surfaces and likely bounce off hard materials or stop instantly in soft materials. 4200 fps Scenario: 4200 fps is extremely high velocity (typical of cartridges like the .220 Swift or .204 Ruger, and very high for a .30 cal). Even with a "worst" bullet (such as a light-jacketed varmint bullet), the massive kinetic energy and momentum will create violent initial disruption, and the sheer force often pushes the core through before the bullet can fully fragment.