A barrel looks like a rigid steel tube, but when you fire, it bends and vibrates, and the bullet goes where the muzzle is pointing at the moment it leaves. So shortening a barrel is more than cutting off the extra length. Along with the length you change how the barrel vibrates, the bullet’s velocity and the muzzle crown, which decides whether the bullet leaves the barrel cleanly.
What barrel harmonics are
Powder gas pressure and recoil bend the barrel, and it starts to vibrate before the bullet has left (Geoffrey Kolbe). The muzzle moves only a tiny amount, but what matters for the shot is less where the muzzle is than where it points: the bullet’s exit angle (Varmint Al). Shooters call these vibrations barrel harmonics, or barrel whip.
The bullet takes about a millisecond to travel down the barrel, and in that time the muzzle completes only part of a vibration cycle. And no two cartridges are identical: velocity varies a little from shot to shot, so bullets leave the barrel at slightly different moments and at slightly different angles.
Hence the key rule: the bullet should leave when the muzzle has almost stopped at the end of its swing. Small differences between cartridges then barely change the exit angle, and the group stays tight. This is the idea behind ladder tests in load development and behind muzzle tuners, weights that change how the barrel vibrates: the added mass reduces the amplitude (Varmint Al).
For long range there is a subtler version, positive compensation. Slower bullets spend longer in flight and drop more. If the bullet exits while the muzzle is still rising, slower bullets start out slightly higher than faster ones and land in the same place. The idea was described as early as 1901 (Geoffrey Kolbe).
How barrel length changes the harmonics
How a barrel vibrates depends on its length, contour and the mass at the muzzle. On top of that, a bullet leaves a shorter barrel sooner. So after a cut, it exits at a different point in the cycle: a rifle that shot well may start to scatter its shots, or the other way round, start shooting better.
The length can be chosen by calculation. The best-known method is OBT, Optimal Barrel Time, by Chris Long. According to it, firing sends a stress wave back and forth along the steel of the barrel at about 5.8 km/s (19,000 fps), making 4 or 5 round trips while the bullet is still inside. Dispersion is lowest when the bullet exits as the bore diameter at the muzzle is changing least, and the model predicts those moments from barrel length alone (Chris Long). Knowing your load’s barrel time, you can find the length at which the bullet exits at such a moment.
It is a model, and ballisticians have questions about it. In his first simulation Long himself left out the bullet’s movement. And Hornady’s ballisticians found that load-development “nodes” disappear with larger samples (Outdoor Life). So a calculation gives you a starting point, and accuracy is confirmed on the range. We calculate the harmonics for your barrel and load so that the barrel length is not left to chance; more on that below.
The muzzle crown: the last thing the bullet touches
The muzzle crown is the face of the barrel around the bore, and “the last thing to touch the bullet before it leaves the rifle” (American Rifleman). As the bullet’s base clears the muzzle, the powder gas rushes out around it. If the edge of the bore is even, the gas escapes evenly. If the crown is damaged or uneven, the gas pushes harder on one side and shoves the base of the bullet sideways (Shooting Sports Retailer).
Factory rifles most often have a rounded or a recessed crown (American Hunter, American Rifleman). For a recessed crown, the muzzle is squared in a lathe and the centre is cut back by 1.3–2.5 mm (.050–.100″), which shields the edge of the bore from knocks and burrs. Another option is the 11-degree target crown: the face is cut at a shallow inward angle, and the rifling ends at the inner edge of the cut (SSR).
Precision matters more than the shape. A bore is never exactly centred in the barrel, so the crown has to be square to the axis of the bore, not to the outside of the barrel, and in the lathe the barrel is centred on the bore (rifleshooter.com).
A rifleshooter.com test shows how much this matters. They shortened the barrel of a .224 Valkyrie with a cutoff wheel and cut the crown with an angle grinder. Before, a group at 100 yards measured 0.55 MOA; after, 1.06 MOA on average, and the point of impact moved about 16 MOA, almost half a metre at 100 m (rifleshooter.com). It works the other way too: gunsmiths have long noticed that recutting the crown often restores a rifle’s accuracy straight away (SSR).
Cleaning from the muzzle: how cleaning rods wore out SKS and Mosin rifles
The Mosin rifle and the SKS carbine both carry their cleaning rod under the barrel, and they were often cleaned from the muzzle end. With a Mosin there is little choice: “military cleaning rods are typically too short to clean from the breech” (7.62x54r.net).
Every pass rubs the steel rod against the rifling near the muzzle. Careless or aggressive cleaning from the muzzle can damage the crown and hurt accuracy, and the many counterbored Mosins are the evidence (7.62x54r.net). Counterboring is done when the muzzle is worn and accuracy has dropped: the bore is drilled out at the muzzle so that a new crown sits on undamaged rifling (7.62x54r.net FAQ). Many M44 carbines were counterbored after the war (Wikipedia).
The SKS designers took this into account: the cap of the cleaning kit kept in the buttstock doubles as a cleaning rod guide that protects the crown during cleaning (Wikipedia). Without the guide, the rod rubs on the crown again.
In the Shooting Sports USA test, one of the four ways to damage a crown was cleaning from the muzzle end, the mildest of them. Even so, the barrel shot worse than before. The magazine’s advice is clear: do not clean from the muzzle end, clean from the chamber end (Shooting Sports USA).
So the rule is: clean the barrel only from the chamber end, pushing the rod from the breech to the muzzle. For a Mosin, use a rod longer than the issue one. If the design does not let you insert a rod from the chamber end, fit a guide on the muzzle, like the SKS kit cap.
And if the rifling at the muzzle is already worn, accuracy can be restored by removing the worn section, either by counterboring or by shortening the barrel, and cutting a new crown on undamaged rifling. We shorten barrels and cut new crowns under licence; more on that below.
How a suppressor affects point of impact
A suppressor is extra mass at the end of the barrel: the MARA Compact S weighs 280 g, the MARA L 380 g and the MARA XL 460 g. Like a muzzle tuner, that mass changes how the barrel vibrates, so the point of impact (POI) usually shifts once a suppressor is fitted (Shooting Illustrated). A 2 MOA shift is not uncommon at all (Silencer Shop).
But a POI shift is not a loss of accuracy. The group with the suppressor may stay the same size or even shrink, and with most suppressors the shift repeats every time (Silencer Shop). What matters is that the suppressor goes on the same way every time: a thread has no positive indexing, so POI can wander slightly with how tightly it is screwed on (Shooting Illustrated). The suppressor should seat firmly against the barrel shoulder, with no washers or jam nuts, and sit in line with the bore; see our article on suppressor alignment with the bore. If the group opens up noticeably with the suppressor, check the mount and whether the bullet is touching the baffles.
Muzzle velocity changes little with a suppressor. In a test by The Firearm Blog it rose by 4–7 m/s (12–22 fps) in six of seven calibres and fell by 3 m/s (11 fps) in .223 Rem (The Firearm Blog).
The takeaway is simple: zero your rifle with the suppressor you will shoot with. If you shoot both with and without it, note the correction for each. How much a suppressor reduces the noise is covered in our article on decibels.
The risks of cutting a barrel yourself
Cutting a barrel with a hacksaw or an angle grinder looks easy. Here is what most often goes wrong:
- A crooked cut. It is too easy for a novice to make a cut that is not square (AccurateShooter), and marking it from the outside of the barrel won’t help, as the bore is not exactly centred.
- Burrs. Sawing and filing leave a burr in the bore that has to be removed before the crown is cut (rifleshooter.com). Left in place, it scrapes the bullet on its way out and pushes it off line too.
- POI shift and flyers. A damaged crown can cause unpredictable flyers that open up the group (AccurateShooter). Shooting Sports USA deliberately damaged the crowns of four barrels, from cleaning from the muzzle end to a hacksaw cut: all of them shot worse and shifted their point of impact (Shooting Sports USA).
- Length by eye. The bullet may end up exiting just as the muzzle is moving fastest, and groups open up even with a clean crown.
- An off-centre thread. If you then cut a suppressor thread without a lathe, the suppressor’s axis won’t line up with the bore. An off-centre thread or crown hurts accuracy even with a good barrel (SSR), and the bullet may strike a baffle.
How much velocity a shorter barrel costs
The shorter the barrel, the less time the powder gas has to accelerate the bullet. Here is what rifleshooter.com found when they cut barrels down an inch at a time and measured velocity after each cut:
| Cartridge | Lost per cm | Example |
|---|---|---|
| .308 Win | 2.5–3.0 m/s | 71 → 42 cm: −86 m/s |
| .223 Rem / 5.56×45 | 2.7–3.6 m/s | 66 → 42 cm: −88 m/s |
| 6.5 Creedmoor | 1.7–2.6 m/s | 69 → 41 cm: −71 m/s |
| 7.62×39 | 1.4–1.5 m/s | 61 → 42 cm: −30 m/s |
Ranges cover the different loads in each calibre, and the example is one of them; your rifle will give different numbers. Per inch, that is roughly 12–30 fps depending on the cartridge. Tests: .308 Win, .223 Rem, 6.5 Creedmoor, 7.62×39.
To know the numbers for your own rifle, measure velocity with a chronograph before and after the cut. For example, the Garmin Xero C1 Pro Doppler radar measures velocities from 30 to 1,500 m/s.
What the law says
In Ukraine, manufacturing and repairing non-military firearms is a business activity that needs a licence from the Ministry of Internal Affairs (Law on Licensing of Business Activities). Under the Ministry’s Instruction No. 622, owners may join and separate the parts of their hunting weapons themselves, but only in ways that need no production facilities or specialised equipment. For fixing defects, the Instruction refers owners to the manufacturer or a workshop licensed by the Ministry. And Article 263-1 of the Criminal Code of Ukraine sets three to seven years in prison for illegal alteration of a firearm.
The same Instruction sets minimum lengths for hunting weapons: a rifled barrel must be longer than 200 mm, and the whole weapon at least 800 mm long. Only parts that cannot be removed without tools count towards the length. A rifled barrel cut to 200 mm or less is treated as a defect, and the permit for that weapon is not renewed.
How we shorten barrels
We work on barrels under licence No. 003610 of the Ministry of Internal Affairs of Ukraine, dated 30.06.2021. To make sure the barrel length is not left to chance, we:
- Calculate the barrel harmonics for your load and work out the length at which the bullet will exit at a good point in the cycle.
- Cut the barrel to that length and machine the crown on a lathe, square to the axis of the bore. The barrel is centred and held in brass mandrels so that it is not damaged.
- Cut a suppressor thread if you need one, make a thread protector and move the front sight if it is in the way.
You can send a barrel from anywhere in Ukraine with a copy of your permit. Prices for threading and crowning are on our services page, and there is more on threading in our article on barrel threading. Message or call us with your rifle model, calibre, the load you shoot and the barrel length you want. Suppressors for your calibre are in our catalogue.
FAQ
Can I shorten a barrel myself?
Technically yes, but it is hard to cut a square, burr-free crown by hand, and a length chosen by eye can ruin accuracy. On top of that, manufacturing and repairing firearms is a licensed activity in Ukraine, and the Criminal Code sets 3 to 7 years in prison for illegal alteration of a firearm.
How short can a rifled barrel be?
In Ukraine, the barrel of a rifled hunting weapon must be longer than 200 mm, and the whole weapon at least 800 mm. Only parts that cannot be removed without tools count (Instruction No. 622 of the Ministry of Internal Affairs).
Does point of impact shift when I fit a suppressor?
Usually, yes: the suppressor adds mass at the muzzle and changes how the barrel vibrates. A 2 MOA shift is common, and with the same suppressor it repeats every time. Zero with the suppressor on, and fit it the same way every time.
How much velocity does a bullet lose if I shorten the barrel?
In the rifleshooter.com tests: 2.5–3.0 m/s per centimetre for .308 Win, 2.7–3.6 m/s for .223 Rem, 1.7–2.6 m/s for 6.5 Creedmoor and 1.4–1.5 m/s for 7.62×39, or roughly 12–30 fps per inch.
Why does the crown need to be cut properly?
So that the powder gas leaves the muzzle evenly and does not push the bullet sideways. The crown must be square to the axis of the bore, with no burrs or dings.
Which end should I clean the barrel from?
Only from the chamber end. A rod pushed in from the muzzle rubs on the rifling at the crown and gradually ruins accuracy. If the design does not allow cleaning from the breech, fit a rod guide on the muzzle.
What is OBT?
Optimal Barrel Time is a calculation method by Chris Long. It looks for the barrel time at which the stress wave in the steel interferes least with the bullet’s exit. It is used to choose a powder charge or a barrel length, and the result is checked by shooting.
