RH or LH rifling twist?

gmd3006 · Oct 19, 2006

In most gun mags, when they do a gun review they'll put in a little data sidebar with pertinent data for the gun. Usually, they'll list the rifling twist rate, and state whether it's RH or LH. Can anyone explain why I should care which direction the bullet twists? I've never actually felt any torque in any gun caused by the angular acceleration of a bullet, so I can't see how it would affect one's hold.

Any clues?

kdub · Oct 19, 2006

Suppose I could get cute and say it depended on which handed the cutter or button puller was, but will admit this is a mystery to me, also.

Sorta like the fact S&W revolver cylinders rotate counterclockwise, while Colt and Rugers go clockwise.

markkw · Oct 19, 2006

C'mon guys, I'm disappointed!!!!

How can you not know that left hand twist is only for use south of the equator??? Simple stuff here folks, flush the toiler down under and it spins the opposite way, thus the rifling has to turn in the opposite direction too.

kdub · Oct 19, 2006

(Slap! - Hitting forehead) How could I not remember that!

M1894 · Oct 19, 2006

kdub said:
(Slap! - Hitting forehead) How could I not remember that!

OLD AGE?????

bob wilson · Oct 19, 2006

Who uses a LH twist,or did the new guy @ Remington put the barrel on backwards

TPV · Oct 19, 2006

gmd3006 said:
In most gun mags, when they do a gun review they'll put in a little data sidebar with pertinent data for the gun. Usually, they'll list the rifling twist rate, and state whether it's RH or LH. Can anyone explain why I should care which direction the bullet twists? I've never actually felt any torque in any gun caused by the angular acceleration of a bullet, so I can't see how it would affect one's hold.

Any clues?

I watched Matt Linhart, a lefty, of the Arizona Cards play against Rex Grossman of the Bears the other night.
Both throw a pretty good spireal.(SP)
I just don't see how physics would effect LH or RH twist since the bullet is totally independant of anything else once it starts forward.

I bet there's an engineer out there who would know.

Cheezywan · Oct 19, 2006

kdub said:
Sorta like the fact S&W revolver cylinders rotate counterclockwise, while Colt and Rugers go clockwise.

From my point of view, you got that backwards. No matter. They do spin opposite.

I remember that my 1957 Plymouth Plaza had lugnuts that were lefthand twist on the passenger side an righthand on the drivers side. I was told (forgotton mechanic) that the "theory was" so that they would tend to get tighter rather than looser during normal rotation. I sure "worked up a lather" fixing my first flat on that car!

It would be interesting to import a toilet with a righthand twist flush! Would it come up rather than go down?

Cheezywan

ribbonstone2 · Oct 20, 2006

]

Might make some small difference at super long range....like in artillery.

Traditonally, Colt's have spun one way (the opposite of cylinder rotation), and S&W's the other (and the opposite of their cylinder's rotation)....US rifle barrels one way, British barrels the other... if it has made any real differnce, the natural variation between barrels hides it.

I certaily wouldn't pay extra fr one over the other, or avoid one just becasue it twisted in the "wrong" direction.
-------
Go back to the fist DA side swing S&W's and you'll find they rotated like Colts (clockwise).

faucettb · Oct 20, 2006

You could split the difference like Taurus did in their new 410 revolvers. They use straight rifling. I've not heard how the 45 colt will shoot in these, but I guess the shotgun does alright.

markkw · Oct 20, 2006

Always with the technical stuff.... you guys are just no fun!

Sorry, I just couldn't resist the southern hemisphere thing!

Actually, there are several reasons for the LH twist, you'll see it generalized that USA mfg's usually use a RH twist while Brits use a LH twist. The most well documented explanation, and the one that makes the most sense comes from the days of big bore rilfes in the man-portable howitzer sizes. It was found that a right handed shooter using a rifle with a RH twist would tend to let the rifle come up and left on recoil which tends to move the POI up and left from the POA. Using the LH twist, this helps cancel out the up & left twisting motion for a RH shooter who's trying to launch a 600+gr chunk of lead with a massive powder charge. Since the majority of shooters are right handed, the lefties didn't get much consideration.

I've never found anything really definitive as to how the American mfg's got hooked on RH twists but most historians seem to agree that since most stuff was based on RH threads, machine builders just went with what was most familiar for them to make. Given the fact that the American builders weren't producing the big african bores, the direction of twist really didn't make much difference.

If you shoot a big bore revolver with a RH twist, use one hand hold and don't put a death grip on the gun, just let it recoil naturally. A full throttle load with a heavy weight bullet will make the muzzle come up and left. If you find a similar gun with LH twist, the muzzle will come strait up without the drift to the left.

As far the bullet coming out the end, it could care less which way it spins and there is no difference in barrel wear, only difference is the direction of rotation.

LET-CA · Oct 20, 2006

I look for rifles with a left-hand twist to match my custom threaded bullet moulds. It allows the bullets to screw themselves into the animal to really plant them on the spot! There's nothing worse that have your bullet bounce around on the surface of an animal because it's spinning the wrong direction.

faucettb · Oct 20, 2006

Mark I happen to like the southern hemisphere thing!

niner · Oct 20, 2006

look here please

kdub · Oct 20, 2006

I think she's full of swirling water, myself!!

Jack Monteith · Oct 20, 2006

I don't want to get into this too deep, but the direction of twist does make a difference at long range.

From Modern Practical Ballistics by Arthur J. Pejsa.

"Coriolis Acceleration"

Due to the earth's rotation, projectile paths drift a slight amount (to the right in the northern hemisphere) over the earth. To visualize this phenomenon, on a merry-go-round rotating counterclockwise, an object thrown between two people will appear to drift or curve to the right. If viewed from the ground, the path does not curve, of course. Due to the earth's rotation, this Coriolis acceleration is:

Y = 2w * V * sin (lat)

where w is earth rotation rate (0.0000729 radians per second), V is average projectile horizontal speed, and lat is latitude. For V = 2800 fps at latitude 45 degrees north, Coriolis is 0.30 fps/s, which is less than 0.01 of that due to gravity. Drift at 100 yards is 0.02 inch to the right, and at approximately 700 yards, is 1 inch to the right. At latitude 45 degrees south, the drift would be the same amount but to the left. Since this extremely small effect is constant and repeatable, it is negligible for most purposes. In naval gun battles at ranges of several miles, however, this effect can be (and has been) significant if not properly accounted for."

(The book gives .0000729 degrees per second, which would make for a very long day.)

Now precession causes a bullet fired from a right hand twist barrel to drift to the right, and adding the Coriolis drift adds up to something that anyone capable of shooting MOA at 1000 yards can notice. I read an article that explains all this in much more detail, but Mark is wrong. The Aussies should shoot with a right-hand twist.

Bye
Jack

markkw · Oct 20, 2006

Well, I'll be..... Thanks, Jack! Since I moved from PA to FL, next time I don't hit where I should, I can blame it on the gun not having been calibrated to the different coriolis effect. My motto is, if you can't dazzle them with your shooting skills, at least baffle them with your elaborate and almost believable BS excuses as to why! LOL

Some points the above doesn't make clear and that can lead to confusion... The earth is rotating west to east as is everything on it. Thus when the projo leaves the muzzle it is also moving west to east at the speed of the earth at that particular latitude.

For the northern hemisphere: If you are shooting to the north, the bullet is moving the east faster than the target is because the target is farther north on the earth. If you're shooting to the south, the bullet moving to the east slower than the target is.

This will be exactly opposite in the southern hemisphere because if you are shooting south, the bullet has a higher west to east velocity than does the target. Reason being is that the bullet does not loose it's west to east velocity when it's fired. The direction of rifling twist should still have no affect but it's one more techno tid bit you can use for an excuse if need be.

Another fun answer for the LH/RH twist question is: "Sometimes the tool & die maker gets mixed up and grinds the rifling cutter the with a LH direction. These tools are expensive so rather than waste it, they just use it till it wears out and then go back to the regular RH cutter."

Cheezywan · Oct 20, 2006

It would seem that I am out of the loop yet again! I have been reading the posts very carefully though.

The best I can make of all of this for a common shooter(that may shoot anywhere on the planet), is to buy a gun that is cross threaded or at least pre-stripped so as to allow easier cross threading? This would allow the bullet to "choose" direction and rate of rotation depending on where and in what direction it is fired?

Thanks to all for helping me sort all this out.

Cheezywan

markkw · Oct 21, 2006

Cheezywan said:
It would seem that I am out of the loop yet again! I have been reading the posts very carefully though.

The best I can make of all of this for a common shooter(that may shoot anywhere on the planet), is to buy a gun that is cross threaded or at least pre-stripped so as to allow easier cross threading? This would allow the bullet to "choose" direction and rate of rotation depending on where and in what direction it is fired?

Thanks to all for helping me sort all this out.

Cheezywan

That would be called a "smooth bore" he he he

Jack Monteith · Oct 21, 2006

It's Friday.

Bye
Jack

gmd3006 · Oct 24, 2006

Thanx, Jack.

Seems like the Coriolis and precession forces would both be nulled out by sight adjustments when I zero my guns' sights. If I travel to South Africa to shoot, I'm gonna rezero to be sure the sights didn't get bumped in transit.

So, I still don't see why one would need to know that datum.

I guess we'll just put it under the category of "trivia".

jean1948 · Nov 2, 2006

In Jack O'Connor's 1961 book: "Complete Book of Rifles and Shotguns" on page 100, states:

" Many rifleman believe that the most accurate twist is the one which will stabilize the heaviest bullet to be shot through a particular barrel at the longest range at which the rifle will be used. There is much to be said for this theory. The more rapid the twist, the higher the pressure and the more the bullet drifts in the direction of it's spin. American barrels with their right-hand twists drift their bullets to the right, just as a baseball with a right-hand spin curves in that direction. Likewise, British barrels with left-hand twists cause their bullets to drift to the left. The rear sight on the Model 1903 Springfield allows for drift. Rifling in Colt revolvers has a left-hand twist, by the way ".

I had to look it up as I knew I read somewhere there were differences in right-hand and left-hand twists.

Lynn · Nov 2, 2006

When shooting in a cross wind the direction of the rifling does make a difference. If the wind is blowing from left to right and the rifling is right hand twist the bullet will impact low right, if the rifling is left hand twist it will impact high right. The bullet has a tendencie to climb the wind if rotating toward it.

kdub · Nov 3, 2006

I think we're straining at knat hairs, here.

Jack Monteith · Nov 3, 2006

The vertical displacement caused by a horizontal crosswind will bite you once you get out to Wimbledon Cup distance (1000 yards). It was a real problem for antiaircraft gunners in bombers during WW II. I forget all the numbers, but the 250 mph crosswind caused enough vertical drift to completely miss a fighter at 400 yards, IIRC.

Here's Sierra's word on the subject.
http://www.exteriorballistics.com/ebexplained/articles/article2.

Bye
Jack

Rocky Raab · Nov 3, 2006

Actually, there is a pretty good engineering reason.

It's because most of our barrels are screwed into the receiver. When a bullet slams into the rifling and starts to turn, the barrel is jolted to turn in the opposite direction (that action/reaction thing of Mr Newton). Selecting the wrong twist direction would mean that the barrel -over time- would tend to loosen in the receiver.

In handguns, there is noticeable torque imparted by the same bullet-meets-rifling thing. (Touch off a Contender in .375 Win or .45-70 some time and see!) In really heavy kickers, having the gun rotate to the left (for right-handers) means the gun rises and turns up towards the left shoulder, easily and cleanly clearing your face. If it torqued the other way, it would tend to come more straight back - right at your nose. When my gunsmith friend Neil Wheeler converts a Ruger Blackhawk to a five-shot .45-70 (!!) he asks the buyer if he's right or left handed, and picks a barrel twist accordingly. He learned to do that when a leftie shot the gun belonging to a rightie once, and planted the hammer spur in his forehead.

RH or LH rifling twist?

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