Novel methods for projectile stabilization?

Elkins45

Elkins45

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We are all aware that rifles and pistols stabilize their projectiles by using tight fitting grooves in the barrel to spin them rapidly. Most are also aware that arrows and smoothbore guns like the M1 Abrams tank are stabilized by aerodynamic drag from fins or fletching at the rear of an elongated projectile. Fletchette rounds from shotguns use the same method. And there is a degree of stabilization given by a weight-forward projectile design like a Minie bullet or Forster slug. Are there any other methods of projectile stabilization that have been used by modern or historical firearms?

Specifically I’m wondering if anyone has ever attempted to use a streamer attached to a bullet base, ideally in combination with a weight forward design like a shotgun slug? I’m imagining casting a hollow based shotgun slug and attaching a streamer up inside the hollow base that unfurls when fired. The streamer would add negligible weight or volume to the slug but might result in a worthwhile increase in accuracy when fired from a smooth bore. There are a number of kids toys that use streamer stabilization because it’s cheap and effective enough for the intended purpose. If you already reoad slugs the extra effort would be minimal and it might give enough of an accuracy improvement to be worthwhile. A strip of cloth, or a cloth drag tethered with braided nylon twine might be tough enough to withstand the shock of firing since they would be protected from the powder blast by the wad cup.

Thoughts? This silly idea just popped into my head for some reason and now I’m curious, since surely I’m not the first to think of it.

I decided to post this here instead of in reloading because more people read here and may be aware of factory loaded ammunition that handloaders may never have seen.
 
A Google search indicates there is an 155mm artillery round that ejects anti-personnel grenades from the base. Those grenades are stabilized and armed by streamers. Not quite what I was thinking of, but somewhat tangentially related…
 
Some bean bag/sock rounds use a streamer. The early versions were square with heavily stitched edges and were not stabilized. Some had a tendency to get sideways and spin. They made grievous injuries that killed some people who were the intended target of less than lethal force.
Aside from 40mm and 12 gauge less than lethal I haven’t seen streamers or trailing stabilizers used.
 
There's a bit more to it than first glance offers, too.

Many finned projectiles induce spin, if at very low rates 100-200 RPM rather than the 20-40,000 RPM of rifled bullets.

Fins are handy where the projectile is required to have a very large length-to-diameter ratio for their end effects. For tank killing, a kinetic projectile wants to be from 15:1 to 17:1 sorts of ratio. That would create problems of friction from the amount of contact surface in a given barrel. And, there would be drag issues in such a barrel too, which could be detrimental to desired velocity.

There are some munitions that use spring-metal fins which create drag. But, those are operate at lower velocities when the fins open as a general rule.

At least barring rockets, which are a separate kettle of fish. What with having the center of propulsive force at the far end of the moment arm to the CG of mass.

We humans have been perfecting ways to stabilize the lumps and rocks we throw for centuries now.
 
Some time ago, I was out at the range and there was a gentleman of obvious Scandanavian origin firing a strange looking rifle. At each shot, he would run downrange with the bullet, tapping it with a stick to keep it on course. I said, "What the heck is this?!?"

And he said, "Yumpin Yimminy! Anoder yerk what ain't heard about Finn stabliization!"
 
Elmer Keith described a tail of heavy fishing line peened into a hole in a round ball for a shotgun.
Not exactly stabilization, he also described “strung buckshot.”
 
Point of information:

That 20-40,000 RPM is a bit low for most modern firearms.

Some varmint rounds approach a quarter million RPM.

.45 ACP 230 GRAIN standard comes out of the 1911 at about 38,250RPM

Follow this:

A gun with a 1 in 12 (1 foot) twist firing a bullet at 1000 feet per second rotates the bullet at 1000 revolutions PER SECOND.

Times sixty seconds IN A MINUTE = 60,000 Revolutions Per MINUTE (RPM)

But if the muzzle velocity is only 850 feet per second, the rotation would be at 850/1000 feet per second.

And since the twist is slower than 1 in 12, this is 12/16 of 1000 feet per second.

Putting that together, we have

12 / twist X velocity /1000 X 60,000 RPM = bullet RPM

Thus 12/16 X 850/1000 X 60,000 =

.75 x .85 x 60,000 = 38,250 RPM for the .45 ACP bullet out of a 1911

Now do that for 3,000 feet per second with a 1 in 9" twist

12/9 X 3,000/1000 x 60,000 = RPM of a typical varmint bullet.

1.3333.... X 3 X 60,000 =239,999 rpm

First time I did that calculation I thought my calculator was broken.

It wasn't

Terry, 230RN
 
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It is easy to get excited over the big numbers but look back at the start, the bullet is turning one revolution per foot.
So is your cleaning brush.

An old gunzine article described a lot of work on shooting "punkin balls" from a shotgun. The experimenter got ball, wad, and bore matched up and was getting range and accuracy better than "rifled slugs."
 
The HEAT training round (M831A1) for the M256 (main gun on the Abrams) is primarily shockwave stabilized at high velocity. To limit is maximum range the fins that are on the actual HEAT round are removed and an extremely shortened fin base is place that slowly spins the round up. The primary stability at high velocity comes from the super sonic shockwave coming off the impact sensor stem impinging on the flat front of the HEAT round. As the round slows down going down range the shock wave angle coming off the tip opens up and eventually no longer impinges on the flat front of the round body allowing the slow spin to cause the round to tumble greatly reducing its maximum range to keep it on smaller training ranges.

m830.jpg

Standard HEAT round, notice long fin tube sticking way down into the propellent volume

m831a1.jpg

Training HEAT notice the very short aluminum stabilizer at the back. The small angled notches in the round slowly spin it up doing down range.
 
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HEAT rounds operate using a shaped charge, and there are all manner of fluid dynamics arguments over whether the plasma and molten metal from the cup are "disrupted" by having the round spin in flight.
The physics of explosions get involved here pretty quickly. TNT deflagrates around 7000 m/s, PBX is around 5k m/s, that's pretty high velocity over the very short distances of a shaped charge cone, and the plasma waver really does not have much time to "disperse" (if it actually does) due to rotational momentum.
 
dbmjr1 said:
The problem, as I see it, with a streamer shotgun stabilized slug the 'streamer' would be forced under immense pressure into the hollow cavity of the slug. It would never deploy.
Taofledermaus has tried experimental slugs like you are describing.

The Diablo shape, like a air rifle pellet, is one of the most stable shapes without spin.
https://www.youtube.com/user/taofledermaus
https://www.youtube.com/user/taofledermaus

https://www.youtube.com/user/taofledermaus​


.
Click to expand...
I went back 12 years and didn’t find something like I’m proposing. There was a rope dart round but the rope was loose and detached in flight.

The deployment problem is easy enough to overcome. Just make the tail of the streamer wide and bulky enough that the tail sits below the slug in the shot cup.
 
Stick-stabilized Congreve Rockets and launcher. Like today's Independence day skyrockets.


Apply the principle where needed.

IIRC, in Willy Ley's "Rockets, Missiles, and Space Travel," he mentioned the stick should be seven times the length of the rocket, but I thought that was excessive... maybe just for military rockets aimed at an enemy.
 
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Linked buckshot was a thing in Europe at some point. I have an older French authored book that goes on about it being recently banned in the early 1970s. I’m not sure it stabilized anything, but was meant to do soft tissue damage on boars.
I recall there being a Confederate double cannon that shot chain linked ball shot. The idea was solid, send it slinging through the enemy line. The technology was lacking. Getting the firing timing right is about as difficult as a nuclear implosion device. It mostly killed it’s own gunners.
 
Strung shot was an attempt to get close patterns. There were also bag and net shot.

In more recent times, the 1960s, there was the Duck Reach shell. A plastic wad completely enclosed the shot charge and in what would have been the cushioning section of a regular one piece wad was a short fuse and three grains of powder. The idea being that the wad would burst well down range, letting the pattern develop from there. It would give a duck size pattern at 80 yards with good pellet energy because the load had traveled most of the distance in one lump, like a slug. The system worked mechanically, the trick was getting hits pass shooting at 80 yards.

We now have better wads and shot filler for the purpose.


The CSA double barreled cannon still stands in Athens, Georgia. Getting both barrels to fire at exactly the same time was pretty much impossible and the notion was a flop.
BUT, chain shot down the same barrel was functional, usually as dismantling shot in sailing ship actions.
 
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Jim Watson said:
Strung shot was an attempt to get close patterns. There were also bag and net shot.

In more recent times, the 1960s, there was the Duck Reach shell. A plastic wad completely enclosed the shot charge and in what would have been the cushioning section of a regular one piece wad was a short fuse and three grains of powder. The idea being that the wad would burst well down range, letting the pattern develop from there. It would give a duck size pattern at 80 yards with good pellet energy because the load had traveled most of the distance in one lump, like a slug. The system worked mechanically, the trick was getting hits pass shooting at 80 yards.

We now have better wads and shot filler for the purpose.


The CSA double barreled cannon still stands in Athens, Georgia. Getting both barrels to fire at exactly the same time was pretty much impossible and the notion was a flop.
BUT, chain shot down the same barrel was functional, usually as dismantling shot in sailing ship actions.
Click to expand...
tmd16556 said:
Linked buckshot was a thing in Europe at some point. I have an older French authored book that goes on about it being recently banned in the early 1970s. I’m not sure it stabilized anything, but was meant to do soft tissue damage on boars.
I recall there being a Confederate double cannon that shot chain linked ball shot. The idea was solid, send it slinging through the enemy line. The technology was lacking. Getting the firing timing right is about as difficult as a nuclear implosion device. It mostly killed its own gunners.
Click to expand...
Neither of these were really done to improve accuracy. They were done to modify the terminal effect of the shot. What I’m considering is how to improve the accuracy of a single projectile.
 
Yeah we kind of diverged into other unconventional loads. Sorry 'bout that... but not much.

But we have covered gyroscopic and aerodynamic stabilization, I can't think of anything else except that guy I mentioned who had really really good round ball loads with no stabilization. Good by shotgun slug standards, at least.
 
Tail drag by fins is a different paradigm than spin stabilization. The purpose of the fins is to induce drag at the tail of the projectile to shift the center of pressure rearward, moving it BEHIND the center of gravity. Spin stabilization is typically still very important in these systems. This is the principle which underlies the importance of "FOC" for archers' arrows - but rather than calculating the center of pressure, we just reference the center of gravity and the physical center of the arrow - when we have less steerage in the rear, less drag, so arrows fly faster, farther, then our center of pressure is more and more forward, so we need more and more forward weight to move the center of gravity forward. If we throw a ton of rear drag, then we need less forward weight on the arrow to retain the same juxtaposition of center of gravity ahead of the center of pressure.

The center of gravity is really the heart of the projectile, and regardless of yaw, the center of gravity should follow the same "point mass" trajectory, while the distance behind that center of gravity falls the center of pressure is a measure of how stable will be the projectile in flight.

Another way of saying this - think of driving in the snow, comparing a front wheel drive vehicle to a rear wheel drive vehicle. In a front wheel drive vehicle, the force is PULLING the center of mass, effectively dragging the tail, which is relatively stable. Rear wheel drive, alternatively, has the force BEHIND the center of gravity, and in some ways, it will be easier for the center of gravity to just slide out of the way than move forward... Less stable... So this position of force relative to the center of gravity is critical - but in the opposite direction of a projectile in flight.

Unfortunately, with bullets, we have very little tail drag compared to our leading tip drag, so the ogive represents the center of pressure, while the rearward positioned lead core pushes the center of gravity far rearward... This isn't ideal for stable flight - this is actually problematic, which is why we spin the ever-loving-hell out of bullets, to impart a ton of gyroscopic stability via angular inertia. An arrow with its center of gravity a handful of inches ahead of its center of pressure is very easily stabilized, while a bullet with its center of mass proportionately a long way behind its center of pressure needs a LOT of spin stabilization...
 
Varminterror said:
Unfortunately, with bullets, we have very little tail drag compared to our leading tip drag, so the ogive represents the center of pressure, while the rearward positioned lead core pushes the center of gravity far rearward.
Click to expand...

And yet best accuracy is usually with open pointed bullets, moving the center of gravity even farther back.
 
Something like a streamer works well for handgrenades & low velocity projos, i think it would be too much drag for a bullet.
 
Harvey Donaldson, who was designing target and varmint rounds back before things got so all fired scientific, showed the effect of ogive vs velocity for best accuracy. He found that a relatively blunt bullet was better at low velocities, spitzers needed some speed.
 
Jim Watson said:
Harvey Donaldson, who was designing target and varmint rounds back before things got so all fired scientific, showed the effect of ogive vs velocity for best accuracy. He found that a relatively blunt bullet was better at low velocities, spitzers needed some speed.
Click to expand...

LOL !

Did he consider the fact that generally, spitzers are longer than blunt-nosed bullets and therefore require higher spin rates than blunt ones. That's maybe where the "speed" comes in: higher RPMs for a given rifling rate.

Just observational, consider the spin rate needed to stabilize a frisbee compared to the spin rate required for a long thin object, say, a broom handle. Or an unfletched target tip arrow.

You will note the low rifling rates in the old muzzle loaders firing ball ("blunt"-nosed) are very slow... as low as one turn in several feet in some cases, whereas modern rifles in, say, 5.56 NATO chamberings, have twists as fast as one turn in 7 inches. (That's where the quarter-million RPM comes in. Someone else bring up .22 Swift bullets coming apart in midflight from the spin; I'm not going to deal with that here.)

The matter of twist rates has loooooooong been a very scientific subject for the military research agencies of every nation and that's where it got to be "all fired scientific." (Someone else bring up the oft-noted "Greenhill Formula," I'm not going to deal with it here.)

Terry, With Sincere Apologies For Describing The Simple All Fired Scientific Principles For Calculating Ballistic RPMs, 230RN
 
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