By making analogies with real guns, some Nerfers have proposed that rifled barrels may be beneficial for Nerf blasters. But is this true? I will examine the two most popular claimed benefits of rifling, that rifling increases range and improves accuracy, and conclude that rifling as implemented thus far has had no significant effect on range or accuracy and it is not likely to have any effect under any circumstances.
First, the reader must realize that these claims are made most often without any backing. The hypothesis that rifling improves accuracy or range is often made based on misunderstandings of what rifling does. Spinning projectiles do not have less drag. Projectiles are spun to improve stability, as I will explain.
Stability of projectiles
A projectile is stable if it flights straight without overturning. This is desirable as the overturning motion reduces accuracy and range.
Rifling is used to improve the stability of a projectile’s flight. But can the stability of a Nerf dart be improved? In general, the answer is no because Nerf darts get their stability from static rather than dynamic characteristics of the dart.
The simplest way to make a stable projectile is to put the center of gravity far in front of the center of pressure. Details as to why this is stable will be later written in the Wiki. Most Nerf darts get their stability in this way; this is why darts are weighted at their nose.
But, most real bullets are made of a single material and they do not have this desirable weight distribution. Spinning the bullet around its longitudinal axis (as rifling does) can stabilize bullets in this case.
So, by simple examination of the mechanisms involved, we can conclude that rifling won’t have any significant effect on darts with the right weight distribution. Those darts are already very aerodynamically stable. There is no reason to rifle as there will not be any real benefit.
Some benefit from rifling seems plausible for very light darts that do not have the right weight distribution. But this is not an argument for rifling necessarily; adding weight to the front is by far the easiest way to stabilize these projectiles. However, this may not seem to be an acceptable choice for some Nerfers. Very lightweight darts may be desirable for safety reasons, however, there are other ways to improve safety of a dart (like reducing the muzzle velocity) that are far simpler than rifling.
Potential disadvantages of rifling
There are many potentially significant disadvantages to rifling that most proponents of the idea are unaware of. I detail the disadvantages that come to mind below.
- Increased friction – If done poorly, the rifling could increase friction in the barrel and potentially reduce performance as a consequence.
- Leaks around projectile – If done poorly, the rifling grooves could allow for air to leak around the projectile, reducing performance.
- Increased complexity of building – Smoothbore barrels are simpler.
- Less translational KE – To have a spinning dart, some of the energy that would have been put into translational kinetic energy and have contributed to range is instead put into rotational kinetic energy. Rifling is beneficial when this trade-off improves stability such that range or accuracy is improved satisfactorily. However, the reduction in translational KE may not be acceptable in all cases.
- Reduction of stability – Poorly made darts may not have their weight distributed evenly around the longitudinal axis of the dart. Spinning could destabilize these darts and reduce range and accuracy.
Examining the accuracy claim with data
In 2009, a Nerfer who went by the handle Landru did some tests to see what effect spinning a dart had on accuracy. He used a setup with a spinning barrel. It is believed that this spinning barrel provides a way to control the spinning without making multiple rifled barrels. The test did not address rifling directly, rather, it addressed the question of whether spinning darts could even improve accuracy.
Landru posted some data that he claimed showed that the standard deviation of the locations of darts spun at 2000 RPM was lower than that from no spinning.
However, Landru neglected any sort of statistical analysis. I made a brief post that demonstrated his methods were flawed. I used an f-test to see whether there was any statistically significant difference between the two groups. Assuming a sample size of 20, I found critical f-values of 0.46 and 2.12 for = 10%. The f-value of was 1.49. As this was between the critical values, the differences were not statistically significant and consequently we can not determine if they were due to the rifling or random chance.
Landru made no follow-up tests.
Examining the range claim with data
Back in perhaps 2003 or 2004, a Nerfer who went by the handle Vassili tested rifled PETG barrels. He found that the average range of rifled PETG was higher than that of smoothbore PETG. Thankfully, Vassili didn’t claim rifling improved range directly. He only offered a tautology: “When it worked, it worked.” But did it work? Can we attribute any of the differences to the rifling and not random chance?
No, we can not. A t-test suggests the two data sets are statistically the same at the = 5% level. The critical t-value is 2.65. The t-value of the test for the mean is 1.21. As this is within the bounds we would expect at the 5% level of error, we can confidently state that rifling did not increase range in this case.
However, it can be shown that rifling increases the standard deviation of the range with an f-test (data to be added later). This should lead to a decrease in precision due to a decrease in repeatability (each shot is more variable). It also shows that more shots will have lower range with rifling. These two disadvantages are significant.
Based on the implausibility of the explanation for the benefit for rifling and the lack of evidence to suggest that rifling provides any benefit for Nerf darts, I conclude that rifling is ineffective at best and harmful at worst for Nerf.