Historical Inquiry

[OIS]

This is regarding the right vs. left turn of the barrel. I mean is there any reason or advantage between the two? Anyone know when the first barrel was turned? Perhaps aboard a ship of the line?

Is there a formula: number of turns, weight of projectile, FPS from barrel that will yield degree of projectile drop?

[Mtn. Medic]

Well, I'll take a stab at part of your question having to do with left and right hand rifling twist. I'm no ballistics expert but I believe (without dragging them out and double checking) all of my firearms put a counter-clockwise spin on the bullet.

A little conjucture and a little fact. Bullet spins counter-clockwise, water going down the drain and most toilets flush counter-clockwise, hurricanes and tornado's all turn counter-clockwise at least in the northern hemisphere anyway. It has to do with the earths rotation.

And years ago in the fire service we were taught to rotate our fire streams counter-clockwise because they supposedly would have more reach compaired to clockwise rotation.

So I'll make the assumption that is the reason all of my firearms put a counter-clockwise spin on their bullets is that they are more stable with that direction of rotation

And I also suppose that in the southern hemisphere, a clockwise rotation would be more favorable.

I honestly don't know for certain but that's my theory.

I'd love to hear a better answer!

[OIS]

thanks for participating. A friend of mine in the USA artillery told me their big guns even calculate for the rotation of the earth! But I am off-subject. What I am interested in is who put in the first riffling, where, and when. Also any formula that might be applicable.

[PUNK]

maybe these will help?

Rifling - Wikipedia, the free encyclopedia

RIFLE BARREL

The Making of a Rifled Barrel, FirearmsID.com

[X-ffdo]

An IRU. Inertial Reference Unit would account for rotational, gravity and other factors involving the calculation of a trajectory because the trajectory of a bullet from a heavy gun would probably be close to a hyperbolic great circle route. I am taking a calculated guess in all this. Of course the bullet spin is for stability, but as far as which type of spin, would be interesting to see what the logic is behind a specific direction of spin. I know that during the war of independence American sharpshooters had rifled barrel, I think the brits did not.
Like I said this is all a calculated guess for me. Good luck in your research!

[Quietpi]

Direction of twist does not make any difference. This is a reference to what is called the "coriolis effect." It is a factor in global weather, and causes cyclonic activity of storms and weather fronts to turn in particular directions at certain latitudes. It is caused by "friction" between the atmosphere and the surface of the earth. However, storms don't all turn the same direction north or south of the equator. it's more complicated than that. And note that the coriolis effect works over thousands of miles of earth-atmosphere interface. And the "friction" is produced, in part, by things like mountain ranges, which are pretty serious bumps.

The idea of toilets and other drains turning one way in the northern hemisphere and the other way in the southern hemisphere does not hold up to examination. Toilets are, in fact, not symmetrical. They're designed to spin the water one way or the other. They achieve the spinning motion in different ways, usually by offsetting the jet that starts the flushing action. Check it out next time you spend some time staring in your toilet. Maybe after your next visit to Sam's Saloon.

Some things like sinks also develop whirlpools while draining. But if the sink or whatever is actually symmetrical, as most are, then the whirlpool is just as likely to go in one direction as another. You can cause it to go either way, or to reverse it, by swirling the water with your finger. You can do the same thing in many toilets, but in that case they will go back to the first direction.

In little things like projectiles, even those of big guns, the coriolis effect is of no effect. But a host of other things do become important with size and range. In armor we entered into the fire control computer things like barometric pressure, temperature and relative humidity. The computer had its own sensors for wind speed and direction. I've never messed with anything that had to consider the earth's rotation, but I've heard that big ships' guns did. I can't rule it out. But coriolis effect? Not a factor.

Too little spin will obviously not stabilize the round enough, or it might slow its spin enough to become unstable before reaching the target. On the other hand, too much spin causes an increase in friction, which can slow the projectile, causing all sorts of problems. Also, in the case of indirect fire weapons, like artillery, a projectile that is stabilized too much will maintain its original attitude, even as its arc drops back toward earth. After the round passes its apex, it will start to expose its side, rather than its nose, to the direction of travel. That is, even without changing its attitude, it will start to travel sideways. This causes all sorts of aerodynamic problems, the projectile becomes unstable, friction increases, etc. In short, you miss.

[WKC]

The Coriolis effect is the result of the rotating reference frame that we are on and not friction. The Newtonian equation of F=ma is only valid when dealing with an inertial reference. The surface of the earth is really not an inertial reference plane. We can get away with treating it as an inertial reference if we are dealing with small movements. For big guns that can launch a projectile tens or hundreds of miles, coriolis may be relevant depending on the accuracy required. Also, it does not travel in a great circle route unless it is capable of mid-course guidance. For a simple point-mass model of a projectile, only atmospheric parameters are involved. For a six degree of freedom model, projectile spin as well as coriolis, and a whole bunch of other parameters, are included in the equation. For those interested, Modern Exterior Ballistics by Robert L. McCoy is an excellent book.

[libertarian]

IIRC, the first rifled barrels were seen in the 15th century, but they weren't widespread until around the time of the Civil War.

Also: The corolis effect is irrelevant on bullets. Colts have left twist, S&W have right twist. The direction doesn't seem to matter.

[Tom98915]

I thought it was simply a preference of the firearm maker...

Now my brain is overloaded!!

[libertarian]

Originally Posted by Tom98915

I thought it was simply a preference of the firearm maker...

Rifling direction is. At the speeds and distances small arms / rifle bullets travel, it has no effect. Artillery is in the air a lot longer over longer distances, and the trajectory is indirect, so the rules are very different.

[Poogsdad]

Originally Posted by Tom98915

I thought it was simply a preference of the firearm maker...

Now my brain is overloaded!!

I'm with Tom98915.

Reading this thread is making my brain hurt!!

Ignorance truly is bliss!!

[WKC]

Originally Posted by libertarian

Rifling direction is. At the speeds and distances small arms / rifle bullets travel, it has no effect. Artillery is in the air a lot longer over longer distances, and the trajectory is indirect, so the rules are very different.

Just to be clear, I believe you mean to say that the Coriolis effect is not relevant to small arms exterior ballistics due to the short range involved but the gyroscopic stability produced by the rifling is relevant to small arms.

And by the way, how did we get into all this physics on a gunsmithing thread!

[X-ffdo]

Don't know...ground frictional force tends to slow down Coriolis force, it is also increased by buildings and ground obstructions, ground frictional force drags against Coreolis force.
In a strong crosswind landing, this may be noticeable, as you will have a last minute wind correction adjustment as you get close to the ground. Specially when you have large hangars and you are landing on the leeward side of them with a strong wind flow, like the Santa Ana winds. A bit of turbulence due to disrupted flow would be usual then. At the last minute, when you are very close to the ground, when you least want it.

[WKC]

Coriolis is only significant when dealing with large scale meteorological phenomenon. If the earth is not rotating, the flow from a high to a low pressure system would follow the pressure gradient in a straight line with no curve in the flow. However, because of the earth's rotation, the flow is affected by the Coriolis effect and thus a low pressure system swirls in a CCW direction in the northern hemisphere and in a CW direction in the southern hemisphere.

Wind flowing pass buildings and other ground obstructions is too small in scale to be affected by Coriolis. What is being felt by the airplane is more the result of turbulent flow as the airflow separates off the side of the object as it is trying to make its way around the obstruction. Very similar to the flow on the upper surface of the wing during a stall.

[libertarian]

Originally Posted by WKC

Just to be clear, I believe you mean to say that the Coriolis effect is not relevant to small arms exterior ballistics due to the short range involved but the gyroscopic stability produced by the rifling is relevant to small arms.

And by the way, how did we get into all this physics on a gunsmithing thread!

You are correct; sorry that was unclear.