Wow, thanks for the description. I do have some guns, I am fairly proficient with both a .45 and an AR-15, but know little about ballistics.
The military versions of the projectile are designed to tumble or fragment on impact, getting around the geneva convention & allowing a weapon with less recoil & flatter shooting to aid "less skilled" or smaller recruits. You can also carry more ammo, but for a long shot a 6.5 mm or .30 cal is better.
The first to design tumbling projectiles, (if I remember correctly) were the brits for the .303. FMJ with hollow nose & a steel core, upon impact the core moves forward in the cavity & causes it to tumble. The Russkies copied this idea for the 5.45x39 which is very accurate & lethal with very little recoil compared to the 7.62x39.