The short answer
Birdshot is many small pellets for birds and clay targets. Buckshot is a few large pellets for larger game and home defense. A slug is one solid projectile for deer and longer shots. Match the gauge and never use a shell longer than the chamber marked on your shotgun.
Gauge and shell length
Gauge is the bore size: 12 gauge is larger than 20 gauge, and .410 bore is the smallest common size. The shell must match the gauge on your barrel.
Shells also come in lengths: 2¾ inch, 3 inch and 3½ inch in 12 gauge. Your barrel says the longest shell it takes. A shorter shell is safe to fire in a longer chamber, though some semi-autos won't cycle light loads. A longer shell than the chamber is never safe.
Birdshot
Birdshot holds dozens to hundreds of small pellets. Smaller numbers mean bigger pellets: #8 and #7½ are standard for clays and doves, #6 and #4 for pheasant and turkey.
Waterfowl hunting in the US requires non-toxic shot, such as steel, bismuth or tungsten, instead of lead.
Buckshot
Buckshot uses fewer, larger pellets. 00 buck ("double-aught") is the classic 12 gauge load, with about eight or nine pellets of roughly .33 inch each in a 2¾ inch shell. #4 buck uses more, smaller pellets.
Buckshot is a common home-defense choice. Reduced-recoil loads are easier to control and shoot well. Pattern your shotgun at the distances inside your home to see how far the pellets spread.
Slugs
A slug is one large projectile, effective on deer out to about 100 yards from a smooth bore and farther from a rifled barrel. Rifled (Foster) slugs are made for smooth-bore barrels; sabot slugs are made for rifled barrels and fully rifled choke tubes.
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Common questions
- What's the difference between birdshot and buckshot?
- Birdshot has many small pellets for birds and clay targets. Buckshot has fewer, much larger pellets for larger game and home defense.
- Can I shoot 2¾ inch shells in a 3 inch shotgun?
- Yes. A shorter shell is safe in a longer chamber, though some semi-automatic shotguns won't cycle light loads. Never fire a shell longer than the chamber marked on your barrel.
- Which slug should I use?
- Use rifled (Foster) slugs in a smooth-bore barrel and sabot slugs in a rifled barrel or with a rifled choke tube.
General information, not professional or legal advice. Always follow your firearm maker's ammunition guidance and your local laws.