Slugs have been around in one form or another for as long as there have been shotguns. The first recognizable modern slug was the Brenneke, developed in Germany in 1898. A felt wad screwed to the rear of the slug acted as a "tail" to keep it from tumbling. Ribs and grooves on the sides of the slug allowed it to swage down as it passed through a shotgun's choke. The version of the Brenneke perfected in 1935 is still with us today and finds favor with many hunters. Numerous other European slugs also use the same basic attached-wad principal that originated with the Brenneke. Many of those rounds are available in this country and they shoot extremely well, especially through smoothbore guns.

In the 1930s, American inventor William Foster designed the slug that bears his name. Unlike the round, terribly inaccurate "pumpkin balls" of his era, Foster's slug was based in part on the Minie ball design. With a heavy nose and a hollow rear, the slug naturally flew nose-forward like a badminton shuttlecock. The slug was "rifled" with a series of angled grooves designed to help it turn in flight. Whether Foster slugs spin enough to aid their stability is debatable, but the grooves do allow the slug to compress as it passes through the gun's choke just like the Brenneke.

Working with Winchester-Western, Foster improved his slug to the point it would shoot five-inch groups at 50 yards and the slugs were first marketed in 1935. Winchester, Remington, and Federal continue to load and sell thousands of Foster slugs to this day. Nowadays, Fosters are bigger around than they used to be, helping them to fill shotgun bores for improved accuracy. They've gained weight, too: the one-ounce 12-gauge slug has replaced the 7/8 ounce as standard, and hunters can choose three-inch, 1 1/4 magnum loads (and with them, recoil in the elephant gun class) as well.

The BRI sabot slug was invented in 1968, and it represented a complete departure in slug design. Originally known as the Kelly-McAlvin .50 Caliber 443 Grain Saboted Projectile (presumably named after its inventors) the actual slug is an hourglass-shaped, .50-caliber bullet loaded into a 12-gauge hull between two plastic sabots. The sabots perform the important function of protecting the slug from deformation in the bore, allowing the slug to retain its original shape for superior accuracy. The rear of the slug is hollow, originally filled with a piece of wooden dowel, so it will fly nose first from an unrifled barrel. Early BRI slugs were not especially accurate, and the new cartridge was largely ignored until the accuracy revolution of the 1980s when the BRI Sabot Slug, as it came to be known, began grabbing headlines. Today, both Winchester and Federal load sabot slugs.