Rifle Barrels 101: Twist Rate, Weight & Barrel Length
In our previous article we discussed which rifle barrels where best for accuracy and durability. Today we are going to progress on this topic by discussing the advantages of various twist rates, weight and barrel lengths. These are important considerations that need to be carefully thought out when selecting or purchasing a new barrel. So which specs – twist, weight and length – are best for your intended use?
The answer to the above question can become fairly complex – or at least too complex to answer in one sentence – relying heavily on your intended use as the shooter. There are however some guidelines that we can provide in summary, before going into more detail later on.
- Barrel Twist – This decision relies on the type and weight of projectiles you intend on using. Heavy projectiles and those with the highest BC’s require a faster twist, while lighter – typically cheaper bulk ammunition – performs better when paired with a slower twist rate.
- Barrel Weight & Length – longer barrels have a few advantages, including increased range and velocity, and a reduction in felt recoil. Lighter barrels on the other hand improve manoeuvrability and lessen the effects of fatigue when handled arduously. In an ideal world, a longer & heavier barrel is always better, but a compromise is often vital depending on your role.
There are however more considerations required than what we have briefly mentioned above. Selecting the ideal barrel characteristics may be an overwhelming task for some, so let’s continue through this blog and ensure that no stone is left unturned.
Should You Choose a Slower or Faster Twist Rate?
Before discussing the advantages of fast versus slow twist rates, let us first explain what barrel twist is? When referring to a barrel’s twist, we are referring to the amount of barrel (the length) that it takes for a bullet to make one complete rotation. For example, a 1:10″ twist means that the bullet makes one complete rotation in the rifling for every 10-inches of barrel. If you had a 1:10″ twist in a 20-inch barrel, you can therefore expect your bullet to make two full rotations before leaving the muzzle.
But why is this important to us, or why does it matter? Well, it all has to do with projectile stabilisation. The rate of twist in a given barrel has a direct influence on the spin imparted onto the bullet, which needs to be sufficient enough for the bullet to match its ballistic coefficient (BC) potential. In simpler terms, pairing the perfect bullet weight to twist rate will ensure the most efficient bullet stability and accuracy during free flight.
The Faster Barrel Twist
A faster twist rate will impart more spin onto the projectile than a slower twist rate, and often requires a heavier bullet. This is because lighter bullets are not well paired with a fast twist due to excess spin, otherwise known as overspin. As a result, a faster twist/spin is often purposefully selected when the shooter intends on shooting a heavier range of bullets. This is particularly useful in heavier low-drag projectiles which are very streamlined and have higher ballistic coefficients. In this case, if the spin is insufficient, the projectile will fail to reach its true potential in both accuracy and effective range.
The Slower Barrel Twist
Now as we can imagine – in contrast to the faster twist – a slower rate of twist will impart less spin onto the projectile. This is suitable for lighter bullets where excess spin would otherwise cause an overspin issue, again resulting in an ineffective trajectory and (possibly) tumbling projectiles from a very early stage. A shooter who intends on using a lighter range of bullets, either due to hunting parameters or cost/bulk ammo availability, will be more suited towards purchasing a barrel with a slower twist.
So then wouldn’t it be safer to select a faster twist, just to be safe? No! The faster you spin a bullet (relevant to its weight), the less accurate it will be. There is no reason to spin a bullet any faster than necessary, as excess spin will result in poor precision and possibly bullet destruction. The decision needs to stem from your intended use as the shooter.
Barrel Twist Stability Analysis
A quick stability analysis – using the Gyroscopic Stability Calculator by Bison Ballistics – will demonstrate how we are able to determine a sufficient or excessive barrel twist for an intended projectile. The cartridge/data parameters for this example are as follows:
- Projectile: 77gr Sierra Tipped MatchKing
- Projectile Caliber: .223in
- Projectile Length: 1.072in
- Rifling Twist: Comparison Between 10″, 9″ and 8″
- Muzzle Velocity: 2750fps
And now for the results.
77gr TMK with 1:10″ Twist
77gr TMK with 1:9″ Twist
77gr TMK with 1:8″ Twist
If we were to add a 1:6″ twist result – which to my knowledge doesn’t exist in this particular AR-15 rifle example – then the undesirable result would be as follows.
As we can see by the results above, the 1:8″ twist is the only suitable barrel to stabilise properly stabilise this particular bullet. A 1:7″ twist would work as well, but these results were not displayed.
In some advanced military weapon systems you may find what is called a progressive twist, otherwise known as gain-twist rifling. This type of rifling starts off with very little twist during the first few inches of bullet travel (during the transition from chamber to throat) enabling the bullet to remain essentially undisturbed and trued to the case mouth. The twist gradually increases as the bullet travels further down the barrel, increasing the spin rate. This spreads the torque along a much longer section of barrel, rather than only at the throat where rifling is eroded through repeated engagement, therefore increasing the longevity of the barrel. This type of twist is far more difficult to produce and comes at a high cost, and is not very common amongst civilian rifles.
Light vs. Heavy Rifle Barrels: Which Is Better?
Another important factor to consider when selecting a barrel is weight. Lighter barrels have their purposes, but when it comes to precision, a thicker heavy barrel always has an advantage. The key is finding the prefect compromise between weight and manoeuvrability.
So what exactly are the advantages of a heavier barrel?
- Well first off, thicker barrels produce more consistent harmonics and less vibrations as the bullet travels down the bore. This promotes consistency
- Also, a thicker barrel will heat up at a slower rate as the rifle is fired repetitively. Why is this an advantage? Firstly, the hotter a barrel gets, the more it shifts from its node (or most accurate state). The second reason has to do with mirage; if a barrel gets too hot, it will generate heat waves that may affect your sight picture when looking through your scope
- A heavier barrel also provides more weight towards the rifle’s front end, which reduces the jump angle and aids in consistency when changing between various firing positions
- Lastly – in theory – a thicker barrel will warp less as it heats up, offering more chance of sticking to the rifle’s zero and maintaining accuracy
When it comes to barrel weight, there are typically four different barrels that come to mind.
- The Pencil Barrel – ideal for lightweight builds where weight, manoeuvrability, and price are more desirable than extreme precision
- Standard Rifle Barrel – a standard barrel advertised as such, typically tapering from breech to muzzle, thinning out towards the crown
- A Heavy Barrel – high precision rifles will often use a barrel with far less taper, called a heavy barrel
- The Bull Barrel – a heavy barrel which is cylindrical all the way from the breech to the muzzle, producing the thickest result
So far the heavier barrel seems like the obvious choice, so what are the cons? Well, heavier barrels add a significant amount of weight to the weapon system, which directly impacts manoeuvrability. Going from a lightweight hunting barrel to a precision heavy barrel can easily double the rifle’s mass, and jumping to a bull barrel can triple it. If a heavy barrel is paramount but weight-saving is essential, then barrel fluting is often desired.
Barrel Length: The Pros and Cons of Long vs. Short
Our final topic of this section on rifle barrels is length. You may or may not know this already, but the length of a barrel has a direct influence on the bullet’s muzzle velocity. Longer barrels will produce a higher velocity, which in turn will increase the rifle’s effective range. At the same time, the longer barrel reduces felt recoil as it allows for more propellant to burn inside of the barrel. This also means that the shooter will experience a quieter muzzle blast along with a reduction in visible muzzle flash.
Varying barrel lengths will also cause different points of impact on a given target, even when using the exact same ammunition. A 20″ barrel for example will shoot flatter – impacting high – when compared to a 14.5″ barrel. Barrel tuning (or load development) is therefore required in order to achieve the most accurate bullet and barrel combination.
Example: at a distance of 450m, an AR-15 with a 14.5-inch barrel will produce a bullet impact around 19cm or 7.5in lower than an AR-15 with a 20-inch barrel. This is due to the slower muzzle velocity and bullet speed.
So once again – since a longer barrel seems superior – what is the downside? The disadvantages to a longer barrel are fairly obvious; they are heavier and more cumbersome, more difficult to manoeuvre in tight spaces, and in some cases some rigidity is lost. So if a longer barrel length is crucial to your needs, but manoeuvrability is of some concern, then an aftermarket chassis with a folding stock may be a worthy option.
If you’d like more detail on long versus short rifle barrels, then read this blog: Is a Longer Rifle Barrel more Accurate?