Barrel Length Impact on Handgun Ballistics
In part one of this three-part series, we looked at performance of the most popular calibers for self-defense and how they performed in testing, now we’ll be looking at how barrel length can affect that performance.
It may seem like an issue of concealability; however, handgun barrel length plays a critical role in bullet velocity, muzzle energy, and the terminal performance (expansion and penetration) of defensive ammunition. If anything, modern thinking has moved to a longer barrel with a shorter grip, as most inside the waistband holsters will conceal 4″ to 5″ barrels easily, but a longer grip is more likely to print.
In this second part of our Caliber Wars Series, we’ll compare five common defensive calibers – .380 ACP, 9mm Luger, .40 S&W, .357 SIG, and .45 ACP – in three general barrel length categories: subcompact (~3″), compact (~4″), and full-size (~5″). We’ll use data from Ballistics By the Inch’s great testing to understand how each caliber is affected by barrel length. While their data is starting to become “old” it is some of the best data available on the subject of velocity and barrel length. We’ll also pull in data from other tests to help inform our conclusions and results.
So with that in mind, let’s answer the questions which rounds lose the most velocity from shorter barrels? Which are least affected? And what barrel length offers the best balance of velocity, expansion, and energy for self-defense?
Table of Contents
How Barrel Length Affects Velocity and Energy
Longer barrels generally allow propellant gases more time to accelerate the bullet, yielding higher velocity and energy. A common rule of thumb is about 50 ft/s gain per inch of barrel for many pistol calibers.
However, this can vary by caliber and load. High-pressure, fast-velocity rounds tend to gain (and lose) more speed with barrel length changes, whereas lower-velocity, heavy-bullet rounds see smaller differences. There are also diminishing returns – beyond a certain length, extra barrel adds little velocity. Below, we examine each caliber in detail:
.380 ACP
.380 ACP is typically fired from very short barrels (often 2.5–3.3” in pocket pistols). In Lucky Gunner’s tests using a ~2.75-3” barrel .380, the average muzzle velocity was around 900 fps for popular self-defense loads. This translates to roughly 180–200 ft-lbs of energy. Such short barrels push the .380 to its lower velocity limits, which can hinder bullet expansion. In gel testing through heavy clothing, .380 JHP bullets showed a median expanded diameter around 0.47 inches and about 13.3 inches of penetration – just above the FBI’s 12” minimum. This indicates many .380 loads barely meet the desired penetration, partly due to limited velocity.
If given a longer barrel, .380 ACP can gain some performance. For example, the Browning 1911-380 (with a 4.25” barrel) produced 100+ fps higher velocity (and ~30 ft-lbs more energy) than typical 2.7–3” barreled .380s. Pushing a 90gr bullet over 1000 fps from a 4”+ barrel can improve expansion reliability. However, practically, most .380 pistols are subcompact; making the barrel longer often means moving up to a 9mm firearm. In short, .380 ACP is low-powered and highly size-constrained: it benefits from a bit more barrel length (to ensure adequate penetration/expansion), but its main advantage is concealability. A subcompact .380 may still be effective with the right load, but it offers the bare minimum penetration and expansion for defense.
Going into the Ballistics by the Inches’ data from the loads they specifically tested we get get the average numbers below.
| 2″ | 1,052 |
| 3″ | 1,158 |
| 4″ | 1,226 |
| 5″ | 1,254 |
| 6″ | 1,290 |
| 7″ | 1,314 |
| 8″ | 1,329 |
| 9″ | 1,346 |
| 10″ | 1,355 |
| 11″ | 1,384 |
| 12″ | 1,397 |
| 13″ | 1,394 |
| 14″ | 1,384 |
| 15″ | 1,396 |
| 16″ | 1,411 |
| 17″ | 1,407 |
| 18″ | 1,441 |
9mm Luger
The 9×19mm Luger is a high-efficiency cartridge that responds notably to barrel length. From a compact 4” service pistol (e.g. Glock 19), typical 124gr defensive JHPs achieve around 1,100–1,150 fps, ~350+ ft-lbs. In a subcompact 3” barrel, velocity often drops to ~1,000–1,050 fps (losing perhaps 50–100 fps).
Conversely, a full-size 5” (or longer) barrel can push standard-pressure 9mm to ~1,200 fps or more. One test that chronographed 25 different 9mm loads in three barrel lengths (Glock 43 at 3.39″, G19 at 4″, G34 at 5.3″) found a distinct, predictable increase in velocity with each length step. The shorter 3.4″ barrel was always slowest, the 4″ mid-level, and the 5.3″ the fastest for any given load. On average, the 9mm lost roughly 10% of its velocity when going from full-size to subcompact barrels. For example, a very light 70gr bullet clocked 1784 fps from the 5.3″ and dropped about 234 fps (~15%) in the 3.3″ barrel, whereas a heavy 147gr load showed only a 54 fps (5.5%) drop across the same range. This illustrates that lighter, high-velocity 9mm loads are more sensitive to barrel length than heavier, subsonic ones.
In terms of defensive performance, 9mm is generally excellent across barrel lengths. Lucky Gunner’s gel tests (using a short “carry length” barrel ~4” or less) showed 9mm JHPs expanding to about 0.58″ on average and penetrating ~17–18″. Even from subcompact pistols, most quality 9mm defense rounds should still meet FBI penetration criteria (12–18″) thanks to modern bullet design.
The main trade-off with a short 9mm barrel is slightly reduced expansion and energy. A compact or full-size barrel can deliver more energy transfer – e.g. a 124gr +P at 1200 fps (~400 ft-lbs) versus the same bullet at 1050 fps (~300 ft-lbs) from a subcompact. That extra velocity can widen the bullet’s expansion and create a bigger permanent cavity. However, beyond ~4–5″ barrels, returns diminish. One study with 3.6″, 4.0″, 4.25″, and 5.0″ 9mm barrels found almost no gain going from 4.25″ to 5″. In fact, the 5″ barrel yielded only ~3 fps more than 4.25″ in that test, suggesting 4 inches is enough to get 9mm near its peak velocity.
It’s worth noting that 9mm outclasses .380 ACP in velocity and penetration even from similar barrel lengths. In one comparison, 9mm had an average muzzle velocity of 1023 fps vs .380’s 903 fps, and penetrated deeper (19.5″ vs 13.3″ in gel on average) with a slightly larger expanded diameter. The 9mm’s greater power comes at the cost of more recoil and typically a larger firearm, but barrel length for length it is far more effective than .380 ACP for self-defense.
Looking at the specific data from Ballistics By The Inch on the 9mm, we get the below averages.
| Barrel Length | Velocity (fps) |
| 2″ | 1,074 |
| 3″ | 1,345 |
| 4″ | 1,444 |
| 5″ | 1,539 |
| 6″ | 1,566 |
| 7″ | 1,619 |
| 8″ | 1,634 |
| 9″ | 1,663 |
| 10″ | 1,647 |
| 11″ | 1,690 |
| 12″ | 1,716 |
| 13″ | 1,738 |
| 14″ | 1,767 |
| 15″ | 1,768 |
| 16″ | 1,740 |
| 17″ | 1,766 |
| 18″ | 1,754 |
.40 S&W
The .40 S&W is a high-pressure cartridge (max ~35,000 psi) launching medium-weight bullets (165–180 gr) at moderate velocities. It is generally tested from a 4″ service barrel (e.g. many .40 duty pistols have 4″ barrels). In that length, a typical 180gr JHP runs ~950–1000 fps (~360–400 ft-lbs), and a 165gr can reach ~1100 fps (~450 ft-lbs).
Shortening the barrel to ~3″ will shave off some speed – roughly on the order of 50 fps per inch (similar to 9mm) as a rule . So a subcompact .40 (3–3.5″ barrel) might drop ~75–100 fps compared to a 4″, slightly reducing energy. For instance, a 180gr bullet that did 980 fps in a 4″ might only do ~900 fps in a 3″ (losing ~80 fps and ~50+ ft-lbs). This is a significant drop, but not as percentage-heavy as in lighter calibers. The heavier .40 bullets retain momentum well, and fast-burning powders in .40 loads mitigate extreme velocity loss.
Still, .40 from a 5″ barrel can gain a bit over the 4″ – one might see a 165gr JHP approach 1150 fps in a longer 4.5–5″ barrel, for example. In practice, though, many .40 S&W defensive guns are in the 3.5–4.5″ range, and within this window barrel length differences are modest.
Lucky Gunner’s data (mostly from ~4″ barrels) showed .40 S&W JHP rounds expanding very widely – median around 0.686″ – while penetrating about 16.5″ in gel. That was the largest expansion of the calibers tested, indicating .40 often creates a large wound cavity. Even if a .40 bullet loses some velocity in a shorter barrel, its larger diameter and weight mean it can still hit hard.
In years past many .40 loads were designed for law enforcement, who often use compact (4″) or full sized (5″) pistols, so modern .40 JHPs tend to reliably expand even at slightly reduced velocities. The main drawbacks of a short-barreled .40 are the pronounced recoil and muzzle blast (the .40 is “snappy”), which can slow follow-up shots. In terms of terminal effect, however, a well-designed 180gr .40 from a 3.5″ barrel can still reach ~14–16″ of penetration and expand to ~0.60″ or more, which is within the effective range for defense.
The bottom line is that .40 S&W does lose some velocity in subcompact barrels, but not enough to negate its effectiveness; a compact ~4″ barrel tends to give near-optimal performance for this round.
Looking for more hard data on this we can look again at Ballistics By the Inch and see the averages across the rounds that they tested.
| Barrel Length | Velocity (fps) |
| 2″ | 964 |
| 3″ | 1,212 |
| 4″ | 1,353 |
| 5″ | 1,453 |
| 6″ | 1,476 |
| 7″ | 1,514 |
| 8″ | 1,537 |
| 9″ | 1,555 |
| 10″ | 1,587 |
| 11″ | 1,591 |
| 12″ | 1,618 |
| 13″ | 1,630 |
| 14″ | 1,649 |
| 15″ | 1,672 |
| 16″ | 1,636 |
| 17″ | 1,650 |
| 18″ | 1,662 |
.357 SIG
The .357 SIG is essentially a 9mm-caliber bullet fired from a necked-down .40 S&W case, achieving magnum-like velocities. It launches ~125 grain bullets at very high speed – often quoted around 1350 fps from a 4” barrel (approximately 500+ ft-lbs of energy). Some boutique loads push 125gr to 1425 fps from a 4″ barrel, essentially replicating a classic .357 Magnum 125gr load in a semi-auto format. This caliber was indeed designed with a ~4” service barrel in mind (Sig Sauer’s P229 and similar), and manufacturers load it to reach advertised velocity out of those compact barrels, not longer test barrels.
If you shorten the barrel below 4”, .357 SIG will shed some of that velocity. In subcompact .357 SIG pistols (like a Glock 33 with ~3.5″ barrel), shooters commonly see a notable drop in speed – on the order of 100–150 fps reduction compared to a 4″, according to anecdotal reports. That could mean a 125gr JHP that does 1350 fps in a duty gun might run around 1200 fps in the short gun. Even so, it’s still roughly on par with a +P 9mm in absolute performance. It’s fair to say .357 SIG experiences one of the larger velocity losses when barrel length is reduced – similar to 9mm or even slightly more – because it starts at such high velocity (a 10% loss of a very high speed is a big fps drop). On the flip side, this round also gains with longer barrels: in a 5” or carbine-length barrel, .357 SIG can exceed 1,450–1,500 fps with certain loads.
In ballistic gel testing, .357 SIG lives up to its reputation for robust terminal performance. Lucky Gunner’s results (with a carry-length barrel) showed a median expansion of ~0.60″ and penetration of ~18.3″ – essentially matching the ideal FBI wound profile. This penetration depth is on the higher end, which isn’t surprising given the caliber’s velocity (the bullet drives deep even after expanding).
In fact, .357 SIG’s energy and penetration closely mimic a .357 Magnum revolver’s performance with the same bullet weight and barrel length. What this means for defensive use is that a compact ~3.9–4.5″ .357 SIG pistol will deliver very effective results (fast expansion and adequate penetration). A subcompact .357 SIG, while still potent, edges closer to 9mm +P performance due to the velocity loss – it may slightly reduce expansion or penetration if the bullet slows below its optimal window. Most .357 SIG ammo is engineered for duty-length barrels, so one should expect some efficiency loss in a sub-4″ barrel (and a dramatic muzzle blast). Overall, .357 SIG is a top performer in energy and penetration, but to get the full “warp speed” effect, a barrel around 4″+ is recommended.
Again we’ll average out Ballistics By the Inch’s Testing for .357 SIG to get an idea of how the average .357 SIG will preform in a given barrel length.
| Barrel Length | Velocity (fps) |
| 2″ | 1,145 |
| 3″ | 1,373 |
| 4″ | 1,491 |
| 5″ | 1,578 |
| 6″ | 1,588 |
| 7″ | 1,641 |
| 8″ | 1,654 |
| 9″ | 1,694 |
| 10″ | 1,708 |
| 11″ | 1,721 |
| 12″ | 1,751 |
| 13″ | 1,759 |
| 14″ | 1,764 |
| 15″ | 1,794 |
| 16″ | 1,768 |
| 17″ | 1,781 |
| 18″ | 1,770 |
.45 ACP
The .45 ACP is a low-to-moderate pressure cartridge (max ~21,000 psi standard) firing heavy bullets (185–230 gr) at relatively low velocities. It is unique in that it’s least affected by barrel length among these calibers. Many .45 ACP loads use fast-burning powder that is fully consumed even in short barrels, and the heavy bullets carry momentum well.
Testing by AmmoLand’s team showed that going from a full-size 5″ 1911 to a subcompact 3.3″ barrel (S&W Shield .45) had minimal impact on velocity – in some cases the shortest barrel even equaled or outpaced a longer one due to normal round to round variance. Across dozens of .45 ACP loads, the differences were tiny: at most 29 fps difference between 3.3″, 3.9″, 4.7″, and 5″ barrels for certain ammo. In other words, a 230gr HST might clock ~830 fps in a 5″ and, say, 800 fps in a 3.3″ – a virtually negligible change in real-world terms.
This is consistent with the idea that .45 ACP was designed for a 5″ barrel but operates at subsonic velocities that don’t rely on long burn times.
With this we can say barrel length is not a critical factor for .45 ACP’s ballistic performance. A 3–4″ barrel .45 can be just as ballistically effective as a 5″, provided you use quality modern ammunition. You don’t gain much by going to a 5″ except a bit of velocity and a longer sight radius for accuracy.
This makes .45 ACP appealing for compact carry guns – you sacrifice little in “stopping power” when you shrink the platform. Just choose a load known to perform out of short barrels (many .45 ACP self-defense rounds are tested in compact 3.5–4″ guns by the manufacturers).
And now let’s look at the .45 ACP results from Ballistics By the Inch and see the averages they came up with.
| Barrel Length | Average Velocity (fps) |
|---|---|
| 3″ | 973 |
| 4″ | 1,048 |
| 5″ | 1,093 |
| 6″ | 1,063 |
| 7″ | 1,071 |
| 8″ | 1,098 |
| 9″ | 1,103 |
| 10″ | 1,121 |
| 12″ | 1,225 |
| 14″ | 1,181 |
| 16″ | 1,196 |
| 18″ | 1,253 |
Which Calibers Lose the Most (and Least) Velocity in Short Barrels?
To directly answer the question of which rounds see the largest velocity loss in short barrels versus which are least affected:
Most Velocity Loss
Generally, high-velocity cartridges like 9mm and .357 SIG see the greatest drop when barrel length is reduced. In tests, 9mm showed a clear velocity “step down” with each inch less barrel .357 SIG, also suffers a noticeable cut in speed (potentially on the order of 10–15% loss going from ~4.5″ to ~3.5″).
These rounds want to have more built up pressure, so a short barrel (3″ range) can’t fully utilize their potential, leading to more unburnt powder and blast. .40 S&W is also high-pressure and will lose velocity in shorter barrels, but its heavier bullets moderate the percentage drop (expect roughly 50 fps per inch of barrel removed). Overall, .357 SIG likely experiences the largest absolute velocity loss (it can easily drop 100+ fps when losing an inch of barrel due to its high starting velocity), with 9mm close behind.
Least Velocity Loss
.45 ACP is the least affected by shorter barrels. Its low operating pressure and heavy bullet result in only minor velocity changes between 5″, 4″, and even 3″ barrels – in one experiment, the 3.3″ .45 was basically as fast as the 5″ for many loads.
In practical terms, you might see virtually no difference in energy whether a .45 round is fired from a subcompact or full-size 1911. .380 ACP also isn’t as dramatically affected by barrel length in terms of percentage loss; because it’s usually fired from very short barrels to begin with, it’s already near its performance floor. That said, going from a ~3″ to ~4″ barrel in .380 can net ~100 fps (which is ~10-12% gain) – not trivial, but .380 starts from a relatively low baseline. So, while .380 does gain with a longer barrel, the caliber is so mild that even short-barrel .380 can sometimes achieve adequate penetration (albeit with reduced expansion).
So, .45 ACP (and to a lesser extent .380) are least affected by barrel length, whereas 9mm and .357 SIG are most affected, with .40 S&W falling in between. This was clearly observed when comparing 9mm vs .45 – the 9mm showed predictable velocity increases with longer barrels, whereas the .45 ACP’s velocity was “relatively unaffected” by barrel length changes.
Finding the Optimal Barrel Length for Defense
Considering penetration, expansion, and energy retention, the “optimal” barrel length for self-defense handguns tends to be in the compact to full-size range – around 4 inches (give or take half an inch). This length provides a sweet spot where velocity is high enough for reliable bullet expansion and sufficient energy dump, but the gun is still convenient to carry. Here’s why:
Subcompact Barrels: ~3"
While certainly concealable, sub-3.5″ barrels can compromise ballistic performance, especially for faster calibers. Lower muzzle velocity can cause some JHP bullets to under-expand or even fail to expand, leading to either over-penetration with a small wound channel or insufficient penetration if the bullet expands but slows too much.
For example, a short-barrel 9mm might have a tougher time getting 14–16″ penetration if its velocity falls below the bullet’s design threshold. Likewise, .357 SIG out of a subcompact will still hit hard, but may not achieve the full fragmentation or expansion it would from a service barrel. In .45 ACP, short barrels still hit almost as hard, but one must choose ammo wisely to ensure expansion.
In summary, most calibers in very short barrels see a drop in terminal performance – not usually catastrophic, but enough that it narrowly meets or can slip under ideal FBI penetration/expansion criteria in some cases (e.g. some .380 JHPs only reached ~9–11″ in tests, prompting use of FMJ or hybrid rounds in short .380s). Your best bet is to find a loading that has been shown to perform well with a sub-compact barrel or is specifically intended for these barrels as they will use a specialized powder loading to get acceptable results from shorter barrels.
If you are going to be running a sub-compact, you might want to look for a loading that is specifically designed around that shorter barrel, as tweaks to powder can help get back the velocity lost from a short barrel.
Compact Barrels: ~4″
A barrel around 4 inches gives what many consider the best balance for defensive use. At this length, all the calibers we examined can reliably meet the FBI penetration standard with quality JHP bullets. The velocity is high enough to ensure proper bullet expansion in .380 ACP on the lower end (as seen with the Browning 4.25″ .380 gaining a crucial 100 fps), and more than enough for 9mm, .40, .357 SIG, and .45 ACP on the higher end.
In fact, most law enforcement agencies issue handguns with 4–4.5″ barrels in 9mm or .40 S&W for exactly this reason – they perform well in gelatin tests and real-world shootings. At ~4″, 9mm and .357 SIG are near their peak velocity, yielding strong expansion and energy transfer without excessive muzzle blast. .40 S&W and .45 ACP also operate very efficiently at this length, with .45 losing virtually nothing compared to a 5″ barrel. The guns are easier to conceal and carry than full-size, yet shoot almost as comfortably.
Full-Size Barrels: ~5″
A longer barrel will typically maximize velocity, which can increase energy and sometimes slightly enlarge bullet expansion. For instance, a 9mm from a 5″ might penetrate a bit less than from a 4″ because it expands more violently (which is actually a good trade-off in wound creation). However, beyond about 4–5 inches, the gains become minimal for most pistol cartridges. As noted, a 5″ 9mm gave virtually no speed increase over a 4.25″ in one study.
So, while a 5″ barrel ensures you’re getting full performance, it doesn’t dramatically out-class a 4″ in terms of stopping power. The benefit of full-size pistols is more about shootability (longer sight radius, lower recoil due to weight) than a major ballistic advantage. Additionally, extremely high velocities from a long barrel can in rare cases cause bullets to over-expand or fragment, possibly reducing penetration – though modern bonded bullets are built to handle a range of velocities. In the testing we’ve reviewed, none of the rounds needed a 5″ barrel to meet the 12–18″ penetration range – even 3–4″ barrels were sufficient with good ammo. Thus, a barrel longer than ~5″ yields diminishing returns in energy/expansion for defensive pistol rounds.
Policing the Brass - Optimal Barrel Length Recommendations
For typical self-defense scenarios, a compact handgun with a barrel around 4 inches is often optimal. It offers a nearly ideal blend of concealability and ballistic performance. At this length, rounds like 9mm, .40 S&W, and .357 SIG will deliver high velocity for robust expansion and a large wound cavity, while maintaining the 12–18″ penetration depth (e.g. 9mm ~18″, .40 ~16″, .357 SIG ~18″ in gel tests). The .45 ACP in a 4″ barrel likewise achieves full expansion (~0.7″) and ~16″ penetration, essentially matching its 5″ performance.
Going shorter than 3.5″ starts to compromise these factors – for example, a 2.75″ .380’s marginal penetration or a 3″ 9mm’s reduced velocity that could cause a JHP to not fully expand due to reduced velocity. Going much longer than 5″, on the other hand, gives only a slight edge in velocity or energy at the cost of a bulkier firearm. I do personally prefer the larger framed handguns for a slightly more comfortable shooting experience, but it’s not a difference that the average shooter should be worried about.
In conclusion, the best balance of velocity, expansion, and energy transfer is generally achieved with a mid-length barrel (~4″) across these common handgun calibers. Such barrels are long enough to generate effective muzzle velocity for hollow-point ammunition to perform as designed, ensuring robust expansion and sufficient penetration, but short enough for practical carry. Each caliber has its nuances – fast calibers like 9mm and .357 SIG thrive on barrel length (benefiting from ~4″ or more), whereas big slow rounds like .45 ACP seem to be very forgiving even in compact guns – but if one had to pick a one-size-fits-most defensive barrel length, around 4 inches is optimal. This is supported by ballistic data and testing, as well as the practical reality that most “duty/carry” handguns have these barrel lengths and most defensive ammunition is tuned for this reality.
In our final part we’ll be exploring the FBI ballistics testing standards and scoring system, and attempting to develop a more holistic scoring system that takes into account more factors than what is normally considered.
