Myth: “Bullets corkscrew through the air and make dramatic wounds because they’re tumbling.” – Busted!

Claim

Some believe that bullets “corkscrew” through the air (tumbling end over end) and that this tumbling causes dramatic wound damage.

Reality

Rifling-induced spin gyroscopically stabilizes bullets so they fly point-forward, not tumbling. There is minor yaw motion (a tiny coning precession/nutation of the bullet’s tip) right after exit, but it quickly dampens as the bullet travels downrange – nothing like an in-air somersault. Spinning a bullet (like throwing a football in a tight spiral) actually prevents end-over-end tumbling. The truly dramatic damage happens after impact: when the bullet enters tissue, it yaws (turns sideways), may deform or fragment, and those phenomena create the large wound cavities. In other words, the chaos is post-impact – yawing and fragmentation in tissue – not due to a mid-air “corkscrew” trajectory.

Why This Myth Lives

People misinterpret things like ballistic gel photos and exaggerated diagrams. They might see a “keyhole” impact on a target (an elongated bullet hole) and assume the bullet was normally tumbling in flight. In reality, keyholes are a sign of instability – the bullet was not properly stabilized (twist rate too slow for its length, velocity too low, or a damaged projectile/barrel). Under proper stabilization, bullets don’t make oblong “sideways” holes; a keyhole means something is wrong, not that bullets are supposed to tumble through the air. This myth is also fed by misreadings of illustrations that show bullet yaw in tissue or exaggerated “spiral” flight paths – leading some to think bullets normally fly in a corkscrew. They do not.

Science & Testing – What Actually Happens

Exterior Ballistics: Point-Forward Flight

When a bullet is fired, the barrel’s rifling imparts spin, giving the bullet gyroscopic stability. We quantify this with a gyroscopic stability factor Sg – using formulas like Miller’s Twist Rule to predict it for a given bullet, twist rate, etc. An adequately stabilized bullet (generally Sg ≥ ~1.3–1.5) will fly point-forward for its entire flight. The bullet’s tip may trace a very small circle (precession and nutation) immediately after leaving the muzzle, but a stable bullet “goes to sleep” downrange, with yaw and precession decreasing with distance. It is not tumbling end over end or carving a huge spiral path in the air. If you calculate your bullet’s stability and get Sg well above 1.0 (ideally ~1.5 for a safety margin), the bullet’s nose will remain gyroscopically aligned into the airflow. In practice, this is like a well-thrown football: it flies nose-first. A marginally stabilized bullet might wobble a bit more, but won’t outright tumble in flight when Sg > 1.0. Only if Sg < 1.0 (under-stabilized) will a bullet lose stability and potentially tumble – often manifesting as those keyholes on targets.

Terminal Ballistics: The Violence is After Impact

The real source of dramatic wounds is what happens on impact and inside the target, not in the air. Ballistics expert Dr. Martin Fackler’s wound profile studies showed that rifle bullets often travel a certain distance point-forward in tissue before they begin to yaw significantly. Once a bullet yaws (turns sideways) in flesh or gel, two things happen: (1) the bullet’s path curves, and it dumps energy rapidly, creating a large temporary cavity (a shock-stretch cavity in the tissue), and (2) if the bullet’s construction and velocity threshold are right, it may deform or fragment, cutting a larger permanent path. Fackler documented that a typical non-deforming FMJ rifle bullet will eventually yaw 180° (ending base-forward) in tissue, but until it yaws it makes a relatively narrow wound tract. For example, a 7.62×39 mm FMJ from an AK-47 can travel several inches in flesh with a small-caliber-size wound channel (like a handgun hole) until it yaws; after yawing, it causes a much larger stretch cavity. If it breaks apart, it can create multiple tracks of damage. That yaw (and fragmentation) is what causes the devastating tissue destruction – not some “corkscrew” flight through the air. High-speed videos and gel tests show bullets striking point-forward, then upsetting (yawing) as they penetrate. The key point: **a properly stabilized bullet delivers its damage when and because it upsets in the target, not because it was tumbling en route.

7.62×39 mm (AK Food): M43 vs. M67 – A Case Study in Yaw

Let’s apply this to a commonly cited example: 7.62×39 mm ammo, where myth proponents often talk about “tumbling.” The Soviet-designed M43 round (123 gr FMJ with steel core) versus the later Yugoslav M67 round (124 gr FMJ lead core) illustrate how bullet design affects yaw in tissue. Fackler’s tests found that the M43 bullet typically travels roughly 25–26 cm in 10% ordnance gelatin (simulating tissue) before yawing significantly. In other words, it tends to stay point-forward for about a foot of travel, causing a narrow wound channel for that distance. This means if it passes through an average human torso without hitting something critical in those first few inches, the early tissue damage is relatively modest – comparable to a handgun wound through soft tissue. By contrast, the M67 bullet (lead core, flat base) yaws much earlier – on the order of ~9 cm (just 3–4 inches) of travel before it turns over. That earlier yaw means the larger temporary cavity and tissue disruption begin much sooner in the track. The M67 still typically does not fragment (it’s still an FMJ), so its wound is mainly due to yawing and the resultant stretching/crushing of tissue, but because it yaws early, it can produce greater damage in the vital area of a target. These specific depths (≈9 cm vs 25 cm) come straight from Fackler’s wound profiles. Translation: With 7.62×39 FMJ ammunition, you generally get point-forward flight in the body followed by yaw – and the timing of that yaw (dictated by the bullet’s shape, core distribution, etc.) determines how destructive the wound is. The difference between M67 and M43 is bullet design, not some bullets “tumbling through the air” more than others. Both bullets fly stable and nose-first in air; the M67’s design just causes it to upset sooner in tissue. If you hear stories of AK rounds “tumbling,” it’s likely describing this yaw in the target, not an in-flight behavior.

Twist & Stability for 7.62×39

Notably, AK-pattern rifles are built to stabilize these bullets in flight. Typical 7.62×39 AK barrel twist rates are around 1:9.45" (240 mm) – for example, one spec from Palmetto State Armory shows a 7.62×39 AK barrel with a 1:9.5" twist. This twist is sufficient to stabilize the common bullet lengths in this caliber. In standard conditions, an M43 or M67 bullet fired from a 1:9.5” twist will have an Sg well above 1.0 (usually in the stable ~1.5+ range). If your 7.62×39 rifle is producing keyholes in targets at short range (holes that are elongated or sideways), that is not normal – it means the bullet isn’t being stabilized properly, due to a mismatch of bullet length to twist, too low velocity, or a problem with the barrel (e.g. damaged crown or rifling). In such cases, the solution is to address the stability issue (use a faster twist barrel for longer bullets, increase velocity if handloading within safe limits, or fix the firearm) rather than claiming that “AK bullets just tumble.” The vast majority of AKs with proper ammo will punch neat round holes in paper at 100 yards. (For instance, 1:9.45” twist will even stabilize some heavier .30 cal projectiles up to a point – but push a very long/heavy bullet or low velocity, and you might see instability.) The key point: Proper twist = no in-flight tumbling. If you do see tumbling, something is off in the system, not a feature of the ammo. (One manufacturer’s listing of 1:9.5” twist for 7.62×39 is shown below for reference.)

Example manufacturer specs (Palmetto State Armory) for a 7.62×39 mm rifle, showing a 1:9.5" twist rate (equivalent to ~240 mm). Such twist rates are standard for AK-pattern barrels and are designed to gyroscopically stabilize common 7.62×39 bullets in flight, preventing any “tumbling” in the air.

“Tumbling” vs. Keyholing – Don’t Mix Them Up

To reiterate, properly stabilized bullets do not tumble in mid-flight. In quantifiable terms, if the gyroscopic stability factor Sg ≥ ~1.3–1.5, the bullet will fly point-forward to the target. “Tumbling” is what happens when a bullet loses stability (Sg well below 1.0) – it may start to swap ends or tumble end-over-end. When that occurs before hitting a target, the bullet’s path and accuracy go haywire. The clearest sign of an in-flight instability/tumble is a “keyholed” bullet hole in your target (the bullet struck sideways) along with awful accuracy. But under normal conditions with the correct barrel twist, you will never see a keyhole in paper at typical distances – because the bullet isn’t tumbling, it’s spinning true. So, “tumbling” is bad (it means instability). By contrast, yawing in tissue is normal terminal behavior for spin-stabilized bullets (and often desired for effectiveness). It’s important not to confuse these: Keyholing = your bullet was unstable in flight (fix your twist or ammo); Yaw in target = the bullet was stable in air and did its intended job of upsetting in the target. Bryan Litz and Berger Bullets recommend aiming for Sg ≈ 1.5 as a design margin, precisely so that bullets remain stable in flight under a variety of conditions. Bullets with Sg in the “marginal” range (say 1.1–1.2) might still fly point-forward (not tumbling) but can have slightly degraded ballistic performance. Even those usually do not keyhole – they just won’t have optimal long-range BC. As Berger’s stability guidance notes, bullets in the marginal stability range typically still fly point-forward to the end of their flight – they don’t suddenly flop around. Bottom line: if you see actual tumbling during flight, that’s an anomaly indicating instability. It’s not a common or desirable thing, and it’s not what causes the destructive wounds in targets – those result from controlled yawing after impact.

Field Test Plan – GunBusters: Forge Edition

To drive this home with real data, here’s a plan to test and demonstrate the truth:

• Target Stability Check (10 yd, 50 yd, 100 yd paper) – Fire groups at close, mid, and 100 yards with the ammo in question. Examine the bullet holes. Are they clean circles or “keyholes”? Stable bullets will punch clean round holes even at 10 yards; if you see oblong/sideways holes at any distance, the bullet is instable at that point in flight. (If so, try a shorter range – if it’s keyholing even at 10 yards, the bullet is tumbling almost immediately out of the barrel, a clear stability failure.) Log the results for each load. Round holes = stable flight; keyholes = instability. If instability occurs, adjust one variable at a time (e.g. test a shorter bullet or higher velocity or examine barrel rifling) to see what fixes it. This will debunk any notion that keyholes are “just because bullets naturally tumble” – instead you’ll show why that bullet was not stabilized.
  
  

• Chronograph & Stability Calculations – Use a chronograph to record the actual muzzle velocity for each load. Then use a stability calculator (Miller Twist Rule or the improved Miller/Courtney formula for modern bullets) to compute the Sg for each bullet based on its length, weight, twist rate, and velocity. This will let you predict which bullets are on the edge. Aim for Sg ≈ 1.5 or above for a comfortably stable bullet in all conditions. If you find a combo giving Sg ~1.0 or below, you’ve likely found your instability culprit. (For example, a very long heavy bullet in a slow-twist AK might calculate to Sg < 1.0 – don’t be surprised when it keyholes.) Document these calculations to show the correlation between low Sg and observed tumbling. This is using known science (Miller’s rule) to predict and confirm stability issues.
  
  

• Ballistic Gel Test (10% gel at 4 °C, with high-speed video) – Set up a block of calibrated 10% ordnance gelatin (at the standard ~4 °C temperature) and shoot each bullet/load into it while filming with a high-speed camera. This will let you see the bullet’s orientation on impact and as it travels through the gel. You should catch whether it enters point-first (a stable bullet will) and then watch for the yaw. Measure the depth at which the bullet yaws significantly (turns sideways) and note if/where it fragments. This replicates Dr. Fackler’s classic “wound profile” approach, providing a visual of point-forward flight into the gel, then the yaw and any fragmentation. The gel block (with rulers or markings) will show the exact yaw onset distance. Expect that a properly stabilized bullet will hit point-first, travel a bit, then yaw. There should be no tumbling in the air before the gel (you can verify frame-by-frame that it wasn’t yawing wildly on the way in – it should strike nose-on). The high-speed footage of the temporary cavity will dramatically show that the big cavity forms when the bullet yaws and/or breaks up, not before.
  
  

• 7.62×39 Specific Trial – M43 vs M67 vs Others – As a special case, test the classic M43 vs M67 FMJ rounds in gel (calibrated the same way). Document the yaw onset distances. We expect to see the M43 go much deeper before yawing (somewhere in the 20–25 cm range), and the M67 yaw much sooner (around 9–10 cm). Record these differences. The wound profiles from your test should mirror Fackler’s results – e.g. the M43 will have a long narrow track that suddenly enlarges deeper in the gel, whereas M67 will show earlier disruption. This will conclusively show that the FMJ’s wounding depends on yaw timing inside the target. To further hammer the point, include a modern expanding or fragmenting 7.62×39 load (like a soft-point hunting round or a modern barrier-blind load). In gel, those rounds will likely expand or yaw almost immediately, creating large damage early – demonstrating how a bullet that doesn’t rely solely on yaw can cause quick damage. None of these rounds will be tumbling in the air; their differences in wound tracks come from design (where/when they upset). By comparing them, you can show readers that a bullet’s construction (steel vs lead core, FMJ vs soft point) and center of gravity determine how it behaves in tissue, not whether it “spins in flight.” Your high-speed videos and gel blocks, placed side by side, would effectively dispel the tumbling myth with observable evidence.
  
  

Shop / Train Smarter

Match your bullet to your barrel. When choosing ammo or barrels, pay attention to bullet length vs. twist rate. Use tools like the Miller stability formula or Berger’s online twist-rate calculator to ensure your setup gives Sg ≥ ~1.4–1.5. Don’t expect an overstabilized “laser beam” – but do ensure you’re not under-stabilized. If you want to shoot heavy-for-caliber, long bullets out of your rifle, you may need a faster twist barrel. For example, don’t shove a long tracer or subsonic load meant for a 1:8” twist into your 1:12” twist rifle and expect anything but tumbling. Values of Sg < 1.0 mean the bullet will be dynamically unstable and likely tumble in flight, so avoid that regime. If you’re seeing weird behavior downrange, run the numbers – it’s science, not voodoo.

Diagnose the target, not the rumor. If your target shows keyholes, don’t brush it off as “oh, bullets must normally tumble.” Instead, fix the issue: check your barrel twist vs bullet, your muzzle velocity, or possible bullet/base damage or crown damage. Keyholes are telling you instability – something is wrong. For instance, if your AK is keyholing at 25 yards, maybe the barrel is badly worn or you’re using unusually long bullets; a new barrel or different ammo will likely solve it. By addressing the cause, you eliminate tumbling – because again, in-flight tumbling is not normal for a properly stabilized bullet. Don’t perpetuate the myth by assuming it’s expected; correct the setup so your bullets fly true.

For 7.62×39 users (and rifle shooters in general), if you want maximum terminal effect (for defense or hunting where legal), choose expanding or fragmenting ammo when possible. FMJ military ammo will yaw and can be effective, but as we saw, its performance is inconsistent – it depends on where in the target that yaw happens. For example, an M43 FMJ might shoot through a thin target before yawing, making a small hole, whereas a soft-point will mushroom or yaw almost on entry, making a larger wound quickly. Modern defensive rifle loads are designed to reliably upset in targets (via expansion or fragmentation), eliminating the guesswork of yaw distance. In short, don’t rely on “tumble” – rely on good bullet design. Your own gel tests will likely make this very clear: rounds that don’t rely solely on yaw produce more consistent wound trauma. If FMJ is all you have, be mindful that shot placement (hitting something vital) is even more important, since yaw might occur late. But the big takeaway for the “tumbling” myth: a bullet that performs better does so because of better terminal mechanics, not because it’s spinning or tumbling differently in the air.

Sources & Receipts

1. Fackler, M.L. (1989). “Wounding Patterns of Military Rifle Bullets,” International Defense Review 1/1989, pp.59–64. – Classic study documenting rifle bullet wound profiles. Fackler’s gelatin tests for 7.62×39 showed the AK-47 M43 FMJ traveling ~25–26 cm point-forward before yaw, whereas the Yugoslav M67 FMJ yawed after ~9 cm, leading to earlier damage. This paper debunks many misconceptions, noting that bullets yaw in tissue because spin that keeps them point-forward in air is insufficient in flesh, and emphasizing that bullet fragmentation (when it occurs) greatly enhances wounding. (URL: ia903201.us.archive.org archive)
   
   

2. Miller, Don (2009). “A New Rule for Estimating Rifling Twist (Miller Twist Rule).” – Introduced a modern formula to calculate required twist for bullet stability, improving on the old Greenhill formula. Miller’s rule computes the stability factor Sg; values >~1.3 are considered stable (Miller suggested 1.3–1.5 as a reasonable stability margin). The formula accounts for bullet length, weight, diameter, and velocity. Many online calculators (e.g., JBM Ballistics) implement it. In short, Miller’s work allows shooters to predict whether a bullet will be gyroscopically stable; a properly stabilized bullet (Sg > 1) will not tumble in flight. (Summary based on JBM Ballistics and Wikipedia)
   
   

3. Courtney, M. & Miller, D. (2014). “A Stability Formula for Plastic-Tipped Bullets” (arXiv preprint 1410.5340). – An updated stability formula recognizing that adding plastic tips/hollow noses to bullets changes their mass distribution. The original Miller formula tended to underestimate stability for modern long-ogive bullets with plastic tips or open tips. Courtney & Miller showed that using the full bullet length in calculations (which assumes uniform density) isn’t accurate for such designs – the plastic tip is lower density and moves the center of mass rearward. Their amended formula improves Sg predictions for these bullets. In practical terms, this research confirmed that many plastic-tipped bullets are more stable than old formulas would predict, so one might be able to use a slightly slower twist than Greenhill/Miller suggest for a given plastic-tipped bullet. (Reference for advanced stability calculations; see also Precision Shooting Jan/Feb 2012 articles.)
   
   

4. Stefanopoulos, P.K. et al. (2014). “Gunshot wounds: A review of ballistics related to penetrating trauma,” Journal of Acute Disease 3(3):178–185. – A scholarly review of external ballistics and wound ballistics. It explains concepts like yaw, precession, and nutation in bullet flight. Notably, it emphasizes that as a stable bullet travels downrange, yaw and precession decrease with distance. The bullet’s nose oscillates slightly right after muzzle exit, but this motion gradually dampens (“goes to sleep”) if the bullet is gyroscopically stable. In other words, a properly spun bullet will fly in a steady state (aligned with its trajectory) and will not progressively spiral out of control. This supports the fact that bullets don’t “corkscrew” around their line of flight if stabilized – any initial wobble is corrected naturally by aerodynamic and gyroscopic forces.
   
   

5. Berger Bullets – Twist Rate Stability Guidance (2020). Berger’s official knowledge-base on using their Twist Rate Stability Calculator and interpreting results. Berger reiterates that: an Sg < 1.0 = unstable, likely leading to bullet yaw/Keyholing and very poor accuracy; Sg 1.0–1.5 = marginal (bullet flies point-forward but with suboptimal aerodynamic performance; it usually won’t tumble, but its BC is reduced); Sg ≥ 1.5 = fully stable, ensuring the bullet reaches its advertised BC and remains point-forward throughout flight. They specifically mention that bullet “keyholing” is an indicator of instability in flight – a crucial point debunking the idea that tumbling is normal. This guidance echoes the Miller rule and Bryan Litz’s recommendations, giving credence from a bullet manufacturer’s perspective.
   
   

6. Example – Palmetto State Armory (PSA) 7.62×39 Rifle Specification. A manufacturer spec sheet for a PSA AK-103 (7.62×39 mm) rifle shows a 1:9.5″ twist rate, typical of AK rifles. This real-world example confirms that industry-standard twists are set to stabilize the ammo – a 1:9.5″ twist will stabilize the common 123–125 gr bullets. If those bullets were meant to “tumble through the air,” a fast twist wouldn’t exist. Instead, the fast twist prevents tumbling, keeping bullets nose-forward. (Many AK barrels worldwide use ~1:240 mm twist for this caliber, in line with this spec.) This refutes the myth by showing the intended design: the guns are literally built to avoid in-flight tumbling.
   
   

7. Hollerman, J. et al. (1990s). “Wound Ballistics of firearm projectiles” – (Additional reading, often cited alongside Fackler). Studies in medical and forensic literature also clarify that yaw in tissue is responsible for enhanced wounding. All spitzer (pointed) bullets will eventually yaw to base-first in a medium like tissue if they don’t fragment, because the center of mass wants to leadia. This is a consistent finding across many tests: the initial straight portion of the wound track is usually narrow until yaw occurs. These works further dispel the notion of in-air tumbling by focusing on where the real changes in bullet orientation happen (in the target, not before). (Ref: J. Trauma articles and NATO wound ballistics workshops.)
   
   

8. U.S. Army Field Manuals / NATO STANAGs on small-arms ballistics – Military docs by design assume bullets are stable in flight. For instance, calculations for trajectory, drift, and penetration all presuppose gyroscopically stable flight (no end-over-end tumbling in air). Limit-cycle yaw (a small persistent yaw oscillation) is a known phenomenon, especially as bullets pass transonic speeds, but this is on the order of fractions of a degree and is bounded – a well-stabilized bullet does not suddenly flip end-over-end unless it’s destabilized by an outside force. (Even 7N6 5.45mm “yawing” bullet got its reputation from yawing in tissue, not in flight.) These official sources support the empirical findings: bullets fly straight, spin-stabilized, and tumble only upon impact or if stability fails.
   
   

Bottom Line: Bullets don’t tumble through the air when fired from a proper barrel – they spin like a drill bit or a football, nose-on. The gruesome wound channels come from the bullet yawing and possibly breaking apart in the target, not from a mid-air tumble. In the case of 7.62×39 mm, the difference between a mild wound and a severe one is when the bullet yaws in tissue (M43 late vs M67 early), not anything the bullet did while in flight. Teach shooters and enthusiasts this reality: spin-stabilized bullets fly true, the “tumbling” that counts happens in flesh. By debunking the mid-air tumbling myth, we foster better understanding of ballistics and can focus on what really matters for performance.