Simplify the following text for a Grade 7 native English-speaking person.
Original: With smaller metal jacketed projectiles ranging from .400 to .620 and velocities around 2000 f they possessed vastly improved trajectory and penetration over their black powder forebears .
Simplified: With smaller metal-cased bullets with sizes from .400 to .620 and speeds around 2000 f , they had a much better trajectory and penetration over the black powder guns .