I thought lead is softer. Why is it considered better for ammunition?
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There are several reasons.
For one, exactly, is more malleable. That means the production is easier.
It’s melting point is also relatively low. And the pouring can be done quite uniformly.
Also it’s more dense. More heavy at the same dimensions. That means it flies more accurate.
Another advantage is that BECAUSE OF it’s softness, it rips more fatal wounds. Where a bullet made of steel for example might just go straight through the body, retaining its shape, the softer lead bullet expands, widening the wound channel and damaging more internal stuff
Lead is good both because it is very dense and weirdly because it is soft.
Most modern firearms use something called “rifling” which is where the term “rifle” for the class of firearms originates from. They are a curving set of grooves inside the barrel which bite into the bullet and cause it to quickly rotate as it leaves the barrel. This aids in maintaining accuracy. A softer metal such as lead or copper allows the bullet to deform to match these grooves instead of just tearing the barrel up.
Of course the main goal of the bullet is to transfer impact energy to the target and being dense helps with this. Think about throwing a pebble at someone vs. a foam peanut, it matters a lot how dense the projectile is. Lead is very dense and fairly common, which is also a great feature. You don’t want to be throwing difficult to find materials downrange because chances are you aren’t finding them again.
Lead is also easily formed. If someone wanted to cast their own bullets they could put a pot over a campfire and melt down lead to pour into an iron mold to create new bullets. Lead melts at 621 F compared to copper at 1,984 F so this wasn’t really possible for other suitable metals.
Finally lead deforming on impact isn’t a bad thing because it would tend to “mushroom” and expand to slow down, dumping impact energy into the target quickly.
I’ll add to the Reddit Rabbit Hole –
It’s pretty rare for modern bullets to be pure lead, because as u/Phage0070 indicated gun barrels are slightly smaller than the bullets which forces the bullet to squeeze through as it goes. Lead is so soft is squishes well, but it also leaves behind a lot of debris and smudges in the barrel, called fouling. Finally, it creates airborne lead which is problematic for obvious reasons. To prevent these we started coating bullets with a harder metal, called “full metal jackets”, these technically have parts there are still exposed lead which are sometimes covered up in ammo called “Total metal jackets”.
As u/Sunhating101hateit points out, leads ability to “smoosh” or “mushroom” upon impact is desirable to impart as much energy on the target as possible vs just passing through. In the case of full metal jacket ammo you lose that smooshing because of the hard outer casing so you can also find “hollow point” ammo where the tip is deliberately exposed to the softer inner metal to allow for maximum expansion AND reducing fouling. These get into Geneva Convention awkwardness though, depending on how you interpret it. There is language that basically says you can’t use expanding ammunition or ammunition that deliberately causes massive internal injuries as technically you’re only supposed to remove soldiers from combat, not go out of your way to slaughter or terrify them. I’ve seen people argue both sides on hollow point military applications and I’m not an expert to weigh an opinion.
Adding to what others said, the same properties that make lead good would make gold even better (and some other metals) except for the cost!
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