A shotgun barrel extension is a steel muzzle attachment that screws onto the barrel of a smoothbore shotgun. We make extensions with an overall length of 15 cm for 12, 16, 20 and .410 gauge shotguns. Inside the extension we machine the choke you need, from cylinder to full, so along with the extra length the shotgun gets a tighter pattern.
What a barrel extension does
- A tighter, more even pattern. The main thing an extension gives you is the choke. It squeezes the shot column, so at the same distance more pellets land on the target. More on chokes below.
- Slightly higher shot velocity. In a longer barrel the powder gases push the load for longer. The gain is modest: experts estimate 4 to 15 fps per inch of barrel (Tom Roster, Field & Stream). For 15 cm that is roughly 7–27 m/s, or 2–7% of a typical 380–400 m/s.
- More energy on target. Pellet energy grows with the square of velocity, so +2–7% velocity means +4–14% energy.
- A smoother swing. Weight up front helps you keep the gun moving with a moving target and not stop it as you fire. That is why long barrels are the choice for long passing shots at birds, as the same authors point out.
- One shotgun, several jobs. A short barrel meant for slugs or close work becomes a tool for longer shots with birdshot: screw on the extension and you are set, take it off and the gun is short again.
- Repairing a damaged barrel. If the muzzle end has bulged or burst, we cut off the damaged section, thread the barrel and fit an extension. The barrel gets its original length back, or even more.
How a choke changes the pattern
A choke is a gradual narrowing of the bore at the muzzle. For a 12 gauge with a bore of about 18.5 mm, constriction is measured in fractions of a millimetre: from 0 mm for a cylinder to 1.0 mm for a full choke. The tighter the constriction, the longer the shot column holds together.
The chart shows how far a choke stretches the useful distance. From a cylinder the pattern is wider than a metre by 23 m, from improved cylinder by 27 m, from modified by 32 m, and from a full choke only at 37 m.
The second measure is the share of pellets inside a 75 cm (30-inch) circle at 35 m (40 yards). This is how shotguns are tested on a patterning board:
| Choke | Constriction | Pellets in a 75 cm circle at 35 m | Use |
|---|---|---|---|
| Cylinder | 0 mm | ≈40 % | Close range, fast targets |
| Improved cylinder | 0.25 mm | ≈50 % | All-round hunting, practice |
| Modified | 0.5 mm | ≈60 % | Medium range, FPV drones |
| Improved modified | 0.75 mm | ≈70 % | Dense pattern |
| Full choke | 1.0 mm | ≈73 % | Maximum range and density |
Percentages are for lead shot, from Wikipedia. Steel shot patterns tighter: the same constriction gives it a pattern about two steps tighter. The millimetre scale is for 12 gauge; for 16, 20 and .410 we agree the constriction with you to suit your bore.
A barrel extension against FPV drones
The shotgun has become a common weapon against drones in Ukraine. Rangers of the Special Operations Forces call the pump-action shotgun the “last line of defence”: it is used to “cut down” an FPV or a small reconnaissance drone once it is already close (ArmyInform). Paratroopers of the 80th Brigade train on clay targets flying at about 70 km/h to imitate an FPV flight path (ArmyInform).
But distances are growing. Large 15-inch fibre-optic FPVs carry a charge close to an anti-tank mine, and a detonation within 10–15 m is lethal for the shooter. The safe distance for engaging such a target is now put at 40–50 m or more (Militarnyi). The farther out a drone is met, the more it matters that the pattern stays together: from a cylinder it is wider than a metre by 23 m.
A short barrel without a choke is handy in a trench or a vehicle, but it throws a wide pattern. An extension adds 15 cm of barrel and the choke you need in one go. For example, the ARMSAN RS-S1 has a 470 mm barrel, and 620 mm with our extension.
Which choke for shooting at drones
The target is small and fast, so a pattern that is too tight hurts as much as one that is too wide: at 9 m a full choke gives a circle of just 23 cm, and it is easy to miss. For FPV drones we recommend a modified choke, 0.5 mm: at 9 m it gives a circle of about 30 cm, and the pattern only grows past a metre at 32 m. For lead shot at longer distances, improved modified (0.75 mm) or full (1.0 mm) will do. Steel shot: no tighter than modified.
As for shot size, army manuals recommend No. 1–5 shot against drones (Militarnyi); these are Eastern European numbers, see the table below.
An extension with a Brita
We make extensions with an external muzzle thread for the Brita muzzle brake-compensator. It reduces recoil and muzzle rise, so the gun comes back on target faster for the next shot.
Example: a shotgun with a 47 cm barrel and no interchangeable chokes. A 15 cm extension with a modified choke and an external thread makes it a 62 cm barrel with a tighter pattern, and a Brita at the end tames muzzle rise. For work in tight spaces the extension comes off.
A barrel extension for hunters
- Get the barrel length back. Many shotguns are offered with interchangeable barrels of different lengths, but they cost more, and in Ukraine buying a new barrel means applying for a permit again. An extension is a muzzle attachment for the barrel you already have, which makes things simpler.
- One barrel for slugs and shot. The short cylinder barrel you carry for boar with slugs becomes a duck or goose barrel: screw on an extension with a choke and you get a tighter pattern and 15 cm more barrel. Take the extension off before firing slugs.
- Long shots at birds. The choke keeps the pattern dense farther out, and the weight up front helps you swing smoothly with the bird.
Slugs and chokes: what is safe and what is not
Firing a slug through a constriction is dangerous. A shot load compresses as it passes through a choke, but a solid slug does not: it is forced through, which can damage or bulge the muzzle end or the extension itself.
So fire slugs only through a cylinder. The exception is a round ball that passes freely through the constriction: check this before firing. If the shotgun has a choked extension, take it off before shooting slugs.
Steel shot is hard and barely deforms in a choke, so through our extensions it is fired only with cylinder, improved cylinder or modified. Improved modified and full are for lead shot only.
| Choke | Lead shot | Steel shot | Buckshot | Slug |
|---|---|---|---|---|
| Cylinder, 0 mm | yes | yes | yes | yes |
| Improved cylinder, 0.25 mm | yes | yes | yes | no* |
| Modified, 0.5 mm | yes | yes | yes | no* |
| Improved modified, 0.75 mm | yes | no | yes | no* |
| Full choke, 1.0 mm | yes | no | yes | no* |
* Except a round ball that passes freely through the constriction.
Shot size table
In Ukraine and across the former Soviet Union, shot is marked with a number. The larger the number, the smaller the shot: neighbouring numbers differ by 0.25 mm, from No. 11 (1.5 mm) to No. 0000 (5 mm). Anything larger than 5 mm is buckshot. Numbers 1 to 10 match US sizes to within 0.1 mm, while the larger US sizes use letters.
| No. | Diameter, mm | US size | Pellets per 32 g of lead |
|---|---|---|---|
| № 11 | 1.5 | — | 1600 |
| № 10 | 1.75 | 10 | 1010 |
| № 9 | 2.0 | 9 | 670 |
| № 8 | 2.25 | 8 | 470 |
| № 7 | 2.5 | 7 | 340 |
| № 6 | 2.75 | 6 | 260 |
| № 5 | 3.0 | 5 | 200 |
| № 4 | 3.25 | 4 | 160 |
| № 3 | 3.5 | 3 | 130 |
| № 2 | 3.75 | 2 | 100 |
| № 1 | 4.0 | 1 | 85 |
| № 0 | 4.25 | B | 70 |
| № 00 | 4.5 | BB | 60 |
| № 000 | 4.75 | BBB | 50 |
| № 0000 | 5.0 | T | 45 |
The last column explains the choice of shot size: the smaller the shot, the more pellets in the pattern and the denser it is, but each pellet carries less energy. The count is for pure lead; in a real shell it differs slightly. Steel is about 30% lighter than lead (7.8 vs 11.3 g/cm³), so a steel pellet of the same size carries less energy.
How we make barrel extensions
- Made of steel. The production extension for the ARMSAN RS-S1 is 45 steel with a deep blued finish and weighs 256 g.
- Overall length is 15 cm. The extension fits an internal or external barrel thread.
- Any choke, from cylinder to full.
- Or for your own choke tubes: we make extensions threaded for Mobilchoke, Rem Choke and other formats.
- With an external muzzle thread for the Brita brake-compensator.
- 12, 16, 20 and .410 gauge, for practically any smoothbore shotgun. We already have drawings for many models; for others we work from the customer’s drawings.
No thread on your barrel? We cut it in Kharkiv. If the muzzle end is damaged, we cut off the bad section, thread the barrel and fit an extension, so the barrel ends up as long as it was, or longer. We work on barrels under licence No. 003610 of the Ministry of Internal Affairs of Ukraine, dated 30.06.2021. You can send a barrel from anywhere in Ukraine with a copy of your permit; more in our article on barrel threading.
Ready-made options: the ARMSAN RS-S1 extension with five choke options and a custom extension for your shotgun, with or without an external thread for a muzzle brake. There is also a Brita adapter with a choke. Message or call us with your shotgun model, gauge and the choke you want, and we will tell you what fits.
FAQ
What is a shotgun barrel extension?
A steel attachment that screws onto the barrel of a smoothbore shotgun. Ours is 15 cm long overall, with a built-in choke from cylinder to full or a thread for your own choke tubes.
Can I fire slugs with an extension?
Only if the extension is a cylinder. Firing slugs through a constriction is dangerous; the exception is a round ball that passes freely through it.
Can I use steel shot?
Yes, through cylinder, improved cylinder and modified, that is up to 0.5 mm. Improved modified and full are for lead shot only.
Which choke is best for shooting at FPV drones?
We recommend modified, 0.5 mm: up close the pattern is still wide enough, and it only grows past a metre at 32 m. For lead shot at longer range, 0.75 or 1.0 mm.
How much velocity does an extension add?
Not much: 15 cm of barrel adds roughly 7–27 m/s, or 2–7%. The main gain comes from the choke.
Which shotguns do you make extensions for?
12, 16, 20 and .410 gauge, practically any smoothbore: Hatsan, Huglu, ARMSAN, Mossberg, Winchester, ATA Arms and others.
Can I fit a muzzle brake to the extension?
Yes, we make extensions with an external muzzle thread for the Brita brake-compensator.
