Birdshot
Many smaller pellets form a pattern. In the U.S. size examples below, a higher birdshot number means a smaller pellet. Lead, steel, bismuth, and tungsten-based products of the same numbered size need not have the same mass or behavior.
THE CARTRIDGE LIBRARY · SHOTSHELL
20 gauge
A conventional shotgun gauge smaller in bore than 16 or 12. Its factory market includes target shot, hunting birdshot, buckshot, and purpose-built slugs.
2A Ledger reference desk · Sources checked October 18, 2026
Read the dimensions
- Folded length · max
- 2.445 in
62.103 mm - Nominal shell class
- 2¾ in
69.850 mm - Bore diameter · min
- 0.615 in
15.621 mm - Rim diameter · max
- 0.766 in
19.456 mm
Know the exact name
At a glance
- Cartridge family
- Shotshell
- Bore specification
- 0.6150 in / 15.621 mmBore minimum
- Factory examples
- 3 shot loadsSelected catalog examples
- Weight in cited examples
- Ounces / pellet countPayload is separate from gauge
20 gauge is identified by its complete cartridge designation. The resource-table alternative is 20 ga. A caliber number, bullet diameter, or family resemblance on its own does not identify ammunition compatibility.
A 20-gauge shell must not be mixed with 12-gauge ammunition or equipment. Color of the hull is not sufficient identification.
Dimensions: open the exact dimensional drawing ↗. The displayed number is bore minimum, rather than an assertion that every manufactured projectile or barrel has this exact diameter.
Origins & evolution
Background & development
The 20 gauge was already an established sporting size when Winchester introduced the Model 1912 pump shotgun. The first Model 12s were offered in 20 gauge before the larger 12- and 16-gauge versions followed. That sequence is a useful reminder that the 20 was a serious field-gun choice, rather than merely a later reduced-size version of a 12-gauge shotgun.
Manufacturers continued developing dedicated 20-gauge platforms throughout the twentieth century. Browning added a 20-gauge Auto-5 in 1958 and a 3-inch Magnum 20 version in 1967. Those introductions trace two enduring strands of the gauge’s appeal: lighter sporting guns and heavier-payload ammunition for hunters seeking more versatility from them. Its place in American skeet added a parallel target-shooting tradition. The gauge’s history consequently spans field guns, autoloaders and competition, with differences in firearm weight and shell length playing as much a part as bore diameter alone.
Historical sources: American Rifleman: original 20-gauge Model 12 chronology ↗ · Browning: 1958 and 1967 20-gauge Auto-5 introductions ↗ · NSSA: World Skeet program and gauge events ↗
Construction changes the story
Loads, variations & specialty offerings
Gauge identifies the bore family. Shot number identifies the approximate diameter of an individual pellet. Ounces describe the combined shot payload, while a buckshot product may specify a pellet count. Shell length is a separate chamber-fit specification, normally referenced to the fired shell.
Buckshot
Fewer, larger pellets are commonly listed by size and pellet count. #4 birdshot and #4 buckshot have very different diameters. Pattern behavior depends on the exact load, firearm, and choke; there is no universal inches-per-yard rule.
Slugs
A slug is a single projectile. Rifled/Foster-type and sabot designs have different barrel recommendations. Federal identifies sabot loads for rifled barrels; follow the exact ammunition and barrel maker’s instructions.
Materials & specialty loads
Lead & bismuth
Lead remains common in target and upland loads where permitted. Bismuth is an alternative material offered in selected sporting loads; compare the maker’s product specification and shotgun/choke compatibility.
Steel
Steel shot has different density and hardness from lead. A shot-size label alone does not reproduce the same pellet mass. Use ammunition approved for the barrel and choke; check current local hunting requirements separately.
Tungsten-based & specialty
TSS and other tungsten-based products can use small pellets and dense payloads. The exact alloy and construction matter. Mixed-shot, reduced-recoil, short-shell, and handgun-marketed products retain their own firearm restrictions.
Compare pellet sizes visually
The two circles use the same screen scale to compare nominal pellet diameter. They are not life-size, do not represent a shot pattern, and do not show an individual load’s pellet count.
See nominal pellet sizes in inches and millimeters
| Pellet | Inches | Millimeters |
|---|---|---|
| #9 birdshot | 0.08 | 2.032 |
| #8 birdshot | 0.09 | 2.286 |
| #7½ birdshot | 0.095 | 2.413 |
| #6 birdshot | 0.11 | 2.794 |
| #5 birdshot | 0.12 | 3.048 |
| #4 birdshot | 0.13 | 3.302 |
| #3 birdshot | 0.14 | 3.556 |
| #2 birdshot | 0.15 | 3.810 |
| #1 birdshot | 0.16 | 4.064 |
| BB birdshot | 0.18 | 4.572 |
| BBB birdshot | 0.19 | 4.826 |
| T birdshot | 0.2 | 5.080 |
| #4 buckshot | 0.24 | 6.096 |
| #3 buckshot | 0.25 | 6.350 |
| #2 buckshot | 0.27 | 6.858 |
| #1 buckshot | 0.3 | 7.620 |
| 00 buckshot | 0.33 | 8.382 |
| 000 buckshot | 0.36 | 9.144 |
Federal: shotshell components and nominal shot sizes ↗
Factory shot-load examples
| Product code | Load family | Shell length (in) | Payload | Shot size | Muzzle velocity |
|---|---|---|---|---|---|
| PWBX209 | Steel birdshot | 3 | 1 oz | 2, 3, 4 | 1,350 fps 411 m/s |
| H200 | Lead field birdshot | 2¾ | ⅞ oz | 6, 7½, 8 | 1,210 fps 369 m/s |
| F203 3B | Lead buckshot | 2¾ | 20 pellets | 3 buck | 1,200 fps 366 m/s |
Explore the published data
Ballistics you can inspect
Shotshell muzzle velocity, pellet patterns, and slug trajectories answer different questions. Birdshot and buckshot cannot be represented as a single bullet curve: individual pellet drag and pattern behavior require a load-specific test. The pellet comparison above shows size, not performance.
Select a legend entry to add or remove its line. Hover or tap a plotted point, or use the position slider. With the graph focused, arrow keys move the inspector. Solid dots identify source points; dashed connectors show estimates between them. Load construction, pressure category, and test setup can differ even at the same grain weight.
Read the original values as accessible tables
20 gauge: factory velocity downrange
| Exact load | Source | Published points |
|---|---|---|
| 275 gr Federal 3-inch copper sabot | Federal | 0: 1900; 25: 1790; 50: 1690; 100: 1500; 150: 1340; 200: 1200 |
| 328 gr Federal 2¾-inch rifled hollow-point slug | Federal | 0: 1600; 25: 1430; 50: 1280; 75: 1160; 100: 1070; 125: 1000 |
| 275 gr Federal 2¾-inch copper sabot | Federal | 0: 1700; 25: 1600; 50: 1510; 100: 1340; 150: 1200 |
Source records for plotted slugs
| Maker / product | Bullet mass | Published construction | Muzzle velocity | Test barrel | Source |
|---|---|---|---|---|---|
| FederalP209 FT | 275 gr 17.82 g | 3-inch copper sabot | 1,900 fps 579 m/s | 30 in | Federal · PDF p. 63 ↗ |
| FederalP208 FT | 275 gr 17.82 g | 2¾-inch copper sabot | 1,700 fps 518 m/s | 30 in | Federal · PDF p. 63 ↗ |
| FederalF203 RS | 328 gr 21.25 g | 2¾-inch rifled hollow-point slug | 1,600 fps 488 m/s | 26 in | Federal · PDF p. 63 ↗ |
Direct answers
Common questions
What is 20 gauge?
A conventional shotgun gauge smaller in bore than 16 or 12. Its factory market includes target shot, hunting birdshot, buckshot, and purpose-built slugs.
Is 20 gauge a shot size?
Gauge or bore identifies the shell and bore family. Birdshot and buckshot size labels describe individual pellets. The load also needs a payload, shell length, material, and exact product identification.
Are similarly named cartridges interchangeable?
A 20-gauge shell must not be mixed with 12-gauge ammunition or equipment. Color of the hull is not sufficient identification.
Are the graph values measured or estimated?
The downrange view uses the exact manufacturer catalog records shown in the source table. Dashed connectors and intermediate inspector values use linear interpolation between the displayed source points. Calculated energy uses the listed bullet mass and velocity.
Does higher energy mean the best load?
Energy is calculated from mass and velocity. It does not establish accuracy, expansion, penetration, pattern density, recoil, or suitability for a particular firearm. Use the exact product documentation and firearm manual.
Trace the facts
Sources & methodology
Compiled by 2A Ledger from the linked standards, manufacturer publications, and identified test records. Checked October 18, 2026. Historical tests and older catalogs retain their original dates; a listing here does not establish current availability.
- SAAMI: dimensional drawing · PDF p. 34 ↗
- Federal: shotshell components and nominal shot sizes ↗
- Federal: 2026 ammunition catalog ↗
- Federal · PDF p. 63 ↗
- American Rifleman: original 20-gauge Model 12 chronology ↗
- Browning: 1958 and 1967 20-gauge Auto-5 introductions ↗
- NSSA: World Skeet program and gauge events ↗
Diameter figures preserve the cited drawing convention. Inch–millimeter conversion uses exactly 25.4 mm per inch. Factory specifications describe the maker’s test setup; your firearm, ammunition lot, temperature, and measuring method can produce different results. This is an educational factory-ammunition reference, not a reloading manual.