Why do some bullets have belted indentations like in this picture?

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this, fucking lowIQs this summer

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It's so when you shoot an intruder and they run away you can collect the bullet and the perps blood will be stored in the ridges for DNA testing.

Generally a crimp groove on jacketed rounds, and lube groove for cast lead.

Cool. Could you exain this further im a noobasauras

Im just guessing but its probably for the same reason large caliber pellets and musket bullets are too. For reduced surf contact with the barrel causing less friction and higher velocity.

Interesting. Do the spaces maybe allow room for the bullet to deform into as the rifling lands squeeze it into shape on its way through the barrel?

A lot of brass cases get crimped around the projectile to prevent them from slipping out/in. The crimp lines give you a location to crimp into without marring up the side of the projectile. If you're using cast lead, the lube cuts back on lead fowling I think.
Pic related is a cast lead bullet with lube--a dry waxy substance.

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Im not sure for centerfire projectiles but for the other projectiles, no. It simply keep more material from touching the rifling which reduces friction. If you have a few ribs touching the rifling its easier to push through than if you had the whole length of the bullet making contact.