A lot of shooters talk about “stopping power” like it is a caliber trait, but penetration is where reality shows up. The bullet has to reach the important stuff, and in handguns that usually means enough depth after it hits bone, heavy clothing, or an odd angle. A big, loud round can feel like a hammer in your hands and still fall short because the bullet expands too fast, sheds weight, or slows down early in tissue.
The trick is understanding that caliber is only the starting point. Bullet design, weight, velocity, and the barrel length you actually carry all change what happens after impact. The rounds below often hit with authority and leave a strong impression, but they can also surprise you by stopping sooner than you expected when the load is built for wide expansion or quick energy dump.
.45 ACP
You feel the .45 ACP, especially in lighter guns, and the wider bullet makes people assume it will always drive deep. In reality, many defensive loads are tuned to open fast and stay within typical penetration targets. That big frontal area becomes bigger fast, and resistance adds up in a hurry, especially when the bullet is built to expand wide in soft tissue.
Where people get surprised is in short barrels and softer bullets. A fast-opening hollow point can make a wide wound and still run out of steam early, particularly after passing through an arm, heavy clothing, or a steep angle. If you move to heavier bullets or tougher designs that hold together, depth often increases, but the classic soft .45 load can stop sooner than the recoil and muzzle flip suggest.
.40 S&W
The .40 has a sharp recoil pulse that makes it feel more powerful than a 9mm, and it often hits steel with a convincing smack. That does not guarantee deep penetration. Many .40 loads expand aggressively, and that expansion can slow the bullet quickly once it hits tissue, because the bullet is presenting a bigger face to push through. In rapid strings, that snap feels serious.
The other factor is velocity out of compact pistols. A lot of .40s live in shorter barrels, where speed drops and the bullet can still open early but lack the momentum to keep pushing. You end up with a round that feels stout and looks great on paper, yet can come up shorter than expected when angles, bone, or heavy clothing complicate the shot.
10mm Auto
10mm has a reputation for being a deep-driving animal, and with hard-cast or heavy controlled-expansion bullets, it can be. The surprise comes when you choose the common personal-defense style 10mm loads that are built to expand big and fast. They can hit hard, flash hard, and still give you less depth than the name on the box implies, especially in soft tissue.
Barrel length matters too. A 10mm in a compact gun can lose enough speed that the bullet’s behavior changes, particularly if it is designed for full-power velocities. Some loads over-expand and slow down early. Others fail to reach their intended expansion window and act inconsistent. The point is that 10mm can penetrate extremely well, but not every 10mm load is built for that job.
.357 Magnum
The .357 Magnum is loud, snappy, and it leaves an impression that makes people assume it will punch through anything. With the right bullet, it can. But many popular .357 defensive loads are lighter, faster hollow points that expand violently. That fast expansion can limit depth more than you would expect from a round with that much blast and such a sharp recoil snap.
Short barrels can change the outcome in a different direction. Out of a snub, velocity drops enough that some bullets fail to behave as designed, either expanding too soon and slowing fast or expanding poorly and shedding energy unpredictably. You still get recoil and muzzle flash, but penetration does not always match the legend, especially with lightweight “manstopper” style loads that prioritize dramatic expansion.
.44 Magnum
The .44 Magnum feels like a serious hunting round, and it can be, but handgun bullets are still handgun bullets. Many .44 loads aimed at defense or medium game use expanding designs that open wide and shed speed quickly. If you hit heavy bone at an angle, that big mushroom can slow down faster than most people expect, even though the impact feels massive.
Recoil can also trick your brain into assuming the bullet must be driving deep. With soft points and hollow points, the .44 can create dramatic damage and still stop sooner than a hard, heavy bullet would. When you switch to hard-cast or tougher controlled-expansion bullets, penetration climbs and stays more consistent through thick tissue. The lesson is that the .44’s “hit” does not automatically equal deep travel.
.41 Magnum
The .41 Magnum sits in that space where people assume it splits the difference between .357 and .44 in every way, including penetration. It can, but a lot depends on the load. Expanding .41 bullets can open wide and slow down quickly, especially in shorter barrels or when the bullet is built to make a big wound in deer-sized animals at handgun ranges.
It also gets carried by people who do not shoot it as much, which leads to less thoughtful ammo choices. When you pick a lighter, fast-opening bullet, you get a hard hit and plenty of recoil, yet the bullet can run out of steam earlier than expected in tough tissue or after clipping bone. With heavier bullets and tougher construction, depth improves. Without that, the .41 can surprise you.
.357 SIG
The .357 SIG feels like it should penetrate forever because it is fast and flat, and it often performs well through certain barriers. But speed can work against you when the bullet is designed to expand rapidly. A fast-opening hollow point can dump energy early and slow down, and the smaller diameter does not guarantee a narrow, deep path once expansion starts and the bullet mushrooms.
Another issue is that many loads are optimized for duty-length barrels. In compact pistols, you can lose speed, and that can change how the bullet opens and how far it goes. You still get that sharp muzzle blast and brisk recoil, which makes it feel like “more,” but the actual depth in tissue can be closer to other service calibers than the reputation suggests, depending on bullet construction.
9mm +P
A hot 9mm load can hit harder than people expect, especially in a light carry gun. That extra speed also tends to make modern hollow points expand more aggressively. When expansion is wide and early, penetration can shrink, and that is where shooters get surprised. The gun feels snappy, the hit feels decisive, yet the bullet may not travel as far as a slower load with tougher construction and better weight retention.
The other trap is assuming more pressure always means more usable performance. In some guns, the added speed is modest, while the recoil and muzzle rise increase a lot, and that can open your groups fast. If your shot placement suffers, you gain nothing. A well-chosen standard-pressure 9mm often penetrates more consistently than a flashy +P load that opens too quickly and loses momentum early.
.38 Special +P
A +P .38 out of a small revolver can feel lively, and it is easy to assume it will penetrate well because it is a revolver round with a long history. The reality is that many modern +P hollow points are tuned to expand in short barrels, which can limit depth if they open wide early. The bullet has less speed than magnum rounds, so it does not have endless momentum to spare after expansion.
The snub revolver factor matters. You can get good expansion, but you can also get inconsistent performance depending on the load, the clothing layer, and the angle. Heavy fabric, an arm hit, or bone can change the outcome fast. With non-expanding wadcutters or tougher bullets, penetration often improves, which surprises people who assumed the harder-kicking load must automatically reach deeper.
.45 Colt
The .45 Colt looks like it should be a deep-penetrating freight train because it throws a big bullet. In many classic loads, it is moving at moderate speed and relies on bullet shape and weight to do the work. When you use soft expanding bullets designed for quick upset, that big bullet can mushroom fast and slow down sooner than you would expect, especially if it expands wide at lower velocity.
A lot of people also mix up the different pressure levels in their minds. Standard .45 Colt loads are not the same as heavy hunting loads built for strong revolvers. If you pick a light, soft bullet and expect it to drill deep, you can be disappointed. With a hard-cast or a tougher flat-nose bullet, it can penetrate very well and break heavy tissue consistently. The cartridge can do both, depending on the load.
.327 Federal Magnum
The .327 Federal Magnum surprises people because it is small and fast, and the recoil and blast in a small revolver make it feel more powerful than its diameter suggests. That speed can drive decent penetration with the right bullet, but many defensive loads are designed to expand quickly. Once they open up, the small bullet can lose steam fast, especially after hitting bone or thick muscle and shedding speed.
Barrel length plays a big role here. In short revolvers, velocity can fall enough that some bullets expand inconsistently, which can reduce depth or create unpredictable results. You still get that high-pressure crack and sharp recoil, so it feels like it should be a deep penetrator. In practice, it can do well, but it can also come up shorter than expected if the bullet is built to open wide early.
.30 Super Carry
The .30 Super Carry is easy to underestimate, but it can feel surprisingly sharp in compact pistols, and the velocity numbers look impressive. That leads some shooters to assume deep penetration is guaranteed. With expanding defensive bullets, the opposite can happen. When a small, fast bullet expands quickly, it can slow down fast and stop sooner than the raw speed suggests, especially through layered clothing.
Another surprise is that bullet design is still maturing across manufacturers. Companies are balancing expansion, weight retention, and depth, and some loads favor a wide, quick-opening wound track for fast upset. If you expect it to behave like a tiny rifle round, you will be disappointed. It is still a handgun cartridge, and it lives inside handgun limits. Choose a load that holds together, and it can be effective. Assume speed alone fixes everything, and it will humble you.
.50 AE
The .50 AE hits like a brick in your hands, and the size of the bullet makes people assume it will plow deep no matter what. In reality, many .50 AE loads are built with big expansion in mind, and the bullet can upset dramatically. Once that happens, drag increases fast, and the bullet can shed speed quicker than most shooters expect, even though the muzzle energy numbers look huge.
The platform matters too. Most .50 AE pistols are large, and users often choose ammo based on recoil feel and spectacle. If the bullet is soft, it can deform heavily and lose penetration, especially after encountering bone. With tougher bullets, you can get more depth and straighter travel, but the common big-mushroom style loads can surprise you by stopping sooner than the caliber name suggests.
.44 Special
The .44 Special feels mild compared to magnums, yet it still delivers a heavy, authoritative push. That big bullet can create impressive results, which makes people assume it also penetrates like a drill. Many .44 Special defensive loads use soft bullets that expand quickly at modest velocity. That can produce a wide wound and still limit depth because the bullet does not have high speed to keep driving after it opens up.
Carry guns in .44 Special are often short-barreled revolvers, and that keeps velocity in a narrow band. Expansion can be good, but penetration can vary more than people expect, especially through heavy clothing or on angled hits that make the bullet work harder. If you want deeper travel, you lean toward heavier bullets and tougher construction. The cartridge can do what you want, but big diameter alone does not guarantee it.
.45 GAP
The .45 GAP was designed to deliver .45-level performance in a shorter package, and it can feel stout in compact pistols. That recoil leads people to expect deep penetration, but many .45 GAP loads mirror .45 ACP defensive design goals: reliable expansion with controlled depth. When the bullet opens early, the big frontal area can slow it down quickly, and the shorter barrel many of these guns wear does not add extra speed back.
Another wrinkle is that you do not have the same broad load selection as more common calibers. That means you are often choosing between a handful of defensive loads that emphasize expansion and consistent feeding. If you expect it to punch deeper than a .45 ACP because it feels snappier in a smaller gun, you can be surprised. It often performs within the same general window, and bullet design drives the result.
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