It seems like it would increase dwell time, and improve the amount of energy the powder could transfer to the bullet.

I don’t THINK it would inhibit expansion - though it might alter it.

It seems like the increased inertia would be worth it/even if it took switching to pure copper, etc to get the bullets strong enough.

(I’m thinking mostly for marginal calibers - short-barreled 38s, pocket 380s, etc.

Though, if it makes a big enough difference, I suppose it would let a… 10MM expand even more.

I think the added friction from an excessive twist would slow the bullet down, thereby decreasing penetration.

They've spent a long time working out what is best. To radically change it would be inviting trouble with excess pressures etc.

Also, handguns just don't generate the kind of velocities that create enhanced RPMs. At least not in the ballpark of rifles.

I can’t imagine how increasing twist rate would enhance the penetration of any nonexpanding handgun bullet to any significant degree. How would that increase inertia?

In all the gelatin tests I’ve seen of FMJ handgun bullets, such short, highly stable projectiles penetrated very deeply from conventional pistol barrels, and farther than is usually deemed desirable. If it were a long, nonexpanding projectile as is common with rifle bullets, then a faster twist rate would enhance stability and possibly allow it to penetrate a little deeper before it upset and started tumbling. Again, though, that would usually be considered to be undesirable from a wounding standpoint.

But if you’re referring to penetrating something other than a BG’s body like through a barrier such as sheet metal or glass, then again I can’t see how a faster twist rate would be better.

It’s believed that a faster spin rate with expanding bullets may increase wounding effects for some reason(s), but that’s not about greater penetration.

Other things being equal twist rates have nothing to do with terminal bullet performance, unless the bullet is tumbling (only experienced it one time with very trashy ammo). So no, it's not really a thing. If you read about external ballistics you'll understand more about it.

Rifling/twist rates in a barrel, whether a pistol or rifle, is about retaining the bullet's in-flight accuracy and preventing tumbling and mostly depends on diameter/length/weight of bullet. Has nothing to do with lethality or terminal performance of the projectile. A plain lead slug or round ball shot from a smooth bore shotgun is just as deadly and performs exactly the same as a lead slug or round ball shot from a rifled shotgun. While the terminal performance is exactly the same, a rifled shotgun will shoot a slug more accurately and consistently over a longer distance than a smoothbore. A tumbling bullet from a smooth barrel or improper twist rate is just as deadly as a non-tumbling bullet, but a tumbling bullet's accuracy will be very poor.

I doubt spin rate affects pistol bullet penetration. At the extreme, note that a tank gun is smoothbore and its hard metal penetrator is fin stabilized.

There WAS some work done on expansion, though.
A soft cast .38 hollowpoint expanded more when shot from a Colt with 14" twist than from a Smith with 18.75" twist.

A conventional bullet that tumbles in flight before striking its target is unlikely to have the same terminal effects as one that flies point forward normally.

Although it won’t be much of an effect at short handgun ranges, most tumbling bullets will lose velocity much faster than normal. In addition, accuracy will be severely limited to nonexistent. Most important for defensive purposes, though, would be the effect of the bullet’s impacting as shown by the two circled holes in the picture.





The picture shows the results of shooting 22 Long Rifle ammunition from a revolver when the bullets were not stabilized and started tumbling in flight. The holes at the upper left of the target sheet show the start of instability, but then it progressed to the point that most bullets were hitting completely sideways or possibly even base first. The impact energy was probably about the same as if the bullets had hit normally, but a bullet hitting sideways would penetrate less, and penetration is an important element of wounding effects. Again, that would vary according to the bullet design. A short, stubby bullet like a 230 grain .45 caliber FMJ projectile would be affected less than a longer bullet, but any benefit from an expanding hollow point—not to mention accuracy—would be lost.

In short, the reason handguns and rifles have rifled barrels is because of the significant advantages that stabilized bullets have for all purposes over unstabilized projectiles.

A) I used the wrong term. I meant momentum, not inertia.

B) The 8.6 AAC seems to penetrate an incredible amount, as a subsonic.

That’s why I was wondering about twist rate.

C) I don’t know about how to increased friction would play against more time for the powder to burn - friction from increased barrel length is offset by more time for the powder to burn.

The momentum of a firearm projectile is dependent upon its mass and speed. Again, I don’t see how its spin rate would affect that.

A faster spin rate always increases stability, and therefore all else being equal, a faster twist rate will allow an elongated projectile to penetrate more deeply before upsetting and losing more speed and penetration due to the increased drag of the medium it’s traveling through. Even air can cause enough drag and instability if the bullet is long enough and the twist rate slow enough.

I am curious, though, about your reference to the 8.6 AAC and its penetration. Do you have a reference you can link to that discusses that? One thing I’ve never seen discussed as a separate topic pertaining to stability is the relationship between bullet length and its diameter and weight, but that obviously has an effect.

For example, a 77 grain 0.224" Sierra MatchKing bullet that’s 0.994 inch long requires a 1/9" twist to be stabilized under “best” circumstances*, whereas a 190 grain 0.308" SMK that’s 1.353 inch long will be stabilized with a 1/12" twist under the same conditions, so bullet length alone isn’t the only thing that affects twist rate and stability.

The stability and penetration of an 8.6mm bullet would probably penetrate more at a particular twist rate due to its diameter and/or weight in relation to its length. Even at low handgun velocities and slow twist rates, short, large diameter FMJ handgun bullets penetrate a long way through test media.

And all that is also probably related to bullets’ sectional densities in some way. Plus, of course, if the bullet expands without tumbling that also affects penetration, and most subsonic bullets I am familiar with do not expand in something like gelatin.

* Per Bryan Litz and Applied Ballistics

I’m still curious what prompted your question, but I found this video that claims a higher rotational rate transfers more kinetic energy to the target.

https://www.youtube.com/watch?v=FlbjdobIWYU

The video shows the impact of two bullets at different rotational rates and claims, based on the appearance of the temporary cavities, that the faster twist rate was more effective.

First, as I mentioned before, it’s long been believed that the rotation rate of an expanding bullet does affect its wounding effects. That’s the usual criticism of tests that attempt to determine how bullets will perform at long ranges by shooting them at short distances, but with reduced charges so that the short range velocity is the same as what it would be at the longer distance. But because muzzle velocity affects how fast the bullet is spinning and because the spin rate decays much slower than velocity through the air, the short range tests aren’t exactly equivalent.

All that being said, the two test shots in the linked video weren’t conducted under exactly the same conditions. The most obvious difference was that the point of impact of the 1/9" rifling rate shot was lower on the block than that of the 1/3". That means there was more medium above the first POI than above the second, and that could have had an effect on the size of the temporary cavity. If we’re going to make claims about differences, it’s imperative that all the other variables be the same. Does that invalidate or at least compromise the claim? Possibly not, but possibly yes.

I am also curious about something else I noticed. It seems that the videos of the bullets stop briefly and then resume. I may be wrong, but if I’m right I can only wonder why that was. Was something edited out? If so, why?

All that aside, it is possible that greater rotational rates transfer more KE sooner to the target. If, however, the target is deep enough to stop the bullet, then the total KE will be the same for both shots. All that can vary is how much KE is transferred when in the course of the bullet’s passage.

To return to the original question, though, and assuming that the Gorilla Ammunition’s claims are correct about how the KE is transferred to and affects the target, what does that mean for handgun ammunition? Faster transfer of KE to a living target can be a benefit, but not always because that can limit penetration of the projectile. Plus, there are ways to manufacture bullets to regulate how fast they expand in media and therefore how and when they transfer their energy. That’s why many manufactures of handgun ammunition try to ensure that their bullets will penetrate far enough in test media, but not too far. The current offerings of premium defensive handgun ammunition seem to do that pretty well, but if someone wants more energy to be delivered to the target, the best way to do that is to rely on more powerful cartridges—as some of us do.

So maybe I keep using the wrong term, but bullets spin to increase their ability to remain stable as the fly through a fluid.

If that spin is increased, it seems like that would improve its ability to remain stable.

Also, it’s additional energy/angular momentum in the system, if the velocity is the same.

As for stuff already being worked out…. Maybe. There’s much more variation in twist rates in pistols than in rifles, and I think cost is probably a significant factor, given that a 4 MOA pistol is considered fairly decent and a GLOCK is considered OK out to 16? MOA before they consider it defective.

Also, powders and bullet composition have changed. I realize that a cast bullet may not be able to be spun as fast as a jacketed/monolith - but that may be worthwhile.

Grand Thumb video on the 8.6 Blackout, with a penetration test.

https://youtu.be/ns96O3ZP0qU?si=FcplmWl-I7QP2aA-

If you can get the bullet spinning fast enough, you could put saw teeth on it and turn it into a flying hole saw.

Another aspect to consider is will the bullet stay together.

Back in the late 1800's Switzerland had an armorer who led everyone into using smaller diameter bullets with compressed black powder charges. At the time most bullets were lead that could range for dead soft to hardened alloys. Once the rifles started hitting in the range of 1700 fps from the muzzle even hardened alloy bullets were coming apart as they left the muzzle. It's why jacketed bullets became not just popular it was essential.

I'll also note that I have an 1892 Winchester that a previous owner had re-barreled by Winchester in 357 Magnum back in the 50's when that kind of service was available. Long story short I like to build 357 Magnum loads for it using Hornady XTP bullets. When I started doing this Hornady was advising that loads used in rifles need to limit the velocity to less than 1800 fps. Turns out my preferred load using 14.6 grains of H110 clocks in at 1620 fps and it's proven to be sub 1 MOA at 100 yards. Note, that was with iron sights off a rest and had the range master acting as my spotter.

So what will happen with faster twist rates? Push it too hard and I expect that you will find that you don't have anything hit the target, the bullet will fragment as it leaves the barrel and produce a giant shotgun pattern with a large hole in the center. BTW I have a 12 gauge Briley Dissipator rifled choke and it will produce smoke ring patterns at 40 yards with #9 shot.

quote:

Originally posted by egregore:
If you can get the bullet spinning fast enough, you could put saw teeth on it and turn it into a flying hole saw.

Some small, short-lived company actually marketed such a cartridge in the late 90's (I can't remember the name).
I can't see that being an advantage; once the bullet enters the body you don't want it to cut cleanly and efficiently, making an exit more likely. You want it to cause maximal energy transfer and tissue damage through mushrooming or tumbling.

quote:

Originally posted by WaterburyBob:

quote:

Originally posted by egregore:
If you can get the bullet spinning fast enough, you could put saw teeth on it and turn it into a flying hole saw.

Some small, short-lived company actually marketed such a cartridge in the late 90's (I can't remember the name).
I can't see that being an advantage; once the bullet enters the body you don't want it to cut cleanly and efficiently, making an exit more likely. You want it to cause maximal energy transfer and tissue damage through mushrooming or tumbling.

I remember seeing an article including that round you are mentioning. The thinking was that the wound, although narrow, would be essentially impossible to repair. Resembling a core sampling of a tree.

As for the Garand Thumb vid, that was fascinating. If I had to guess, I'd say there was cavitation involved in that unstoppable penetration. Yeah, maybe high enough RPM with the proper tip design...

quote:

Originally posted by egregore:
If you can get the bullet spinning fast enough, you could put saw teeth on it and turn it into a flying hole saw.

It's fun to multiply and get huge numbers of rpms, but remember, that bullet is only making one turn per ten inches of forward travel.

I would ask
At what Distance, weight and speed?

quote:

Some small, short-lived company actually marketed such a cartridge in the late 90's (I can't remember the name).

I don't remember the company either, but the bullet was called a "Pin Grabber." It wasn't marketed as an anti-personnel bullet, but for shooting bowling pins. The idea was that the teeth would bite into the pin instead of glancing off to compensate for an imperfectly centered hit. Somebody else got the "flying hole saw" idea.