[Petronski]

Some states (NY, I think) do not permit hunting deer with long rifles (some excuse like 'the ground is too flat, who knows where the bullet ends up), so shotgun slugs (literally 'buckshot') are used.

[Gun142]

I cast and load the [Lyman] slugs in the left side of the pic.

525 gr, .685" diameter chunk of lead hits real hard.

[ASA Vet]

Your photo shows "slugs" which are not the same thing as "buck shot."
A slug is one piece, buck shot is multiple round balls.
Double 00 buck is IIRC .32 inches in diameter.
A standard 2 3/4" 12 ga 00 buckshot shell contains 12 of them.

They have been used for hunting deer since the 1800's.
That's why they're called "buck shot."

[jscd3]

so shotgun slugs (literally 'buckshot') are used.

Not exactly. A slug is what you have in you picture - a single solid shot of several hundred grain size. Buckshot is a round countaing multiple (9-12) small (28-32) caliber projectiles.

Buckshot is different from other shot (waterfowl, skeet, etc) only in the size of the projectiles (larger) and number per round (smaller)