Left hand barrel twist?

[Sneaky Apasum]

Supposedly, a left hand twist can help negate drift by counteracting some of the effects of Coriolis with spin drift going the other way, in the northern hemisphere. If so, why aren't left hand twists more common?

I've heard that the torque of firing a bullet from a left hand twist can loosen right hand threads on a barrel. I've also heard that out to a thousand yards or so, coriolis and spin drift aren't worth dealing with. This coming from experienced long range shooters.

What are your thoughts on all of it?

 

[excaliber]

Like the reverse toilet flush this would only work well south of the equator.

 

[Bravo 4]

@ 1000:
Coriolis...no
Spin drift...probably

At 1000 I adjust .5 moa for my .338 and 1 moa for my .308 and this seems to put me on target with more accuracy.

As for left twist barrels unscrewing, I would say it isn't beyond reproach. I don't know. I do know that there is a weapon system the we got new a few years back that the barrel could be unscrewed by hand, and you shouldn't be able to. After speaking to a rep from the manufacturer it seems that when you initially fire it the barrel gets torqued down. After the first firing session of several hundred rounds with the barrel starting off only hand tight, you could not get it to budge afterwards. All that told me really is that it wasn't test fired much if at all before we got it.

 

[LRSickle]

Coriolis would effect you more when shooting south to north. It's just the opposite of a right hand twist. Not that I know anyone who can tell the difference.

 

[Frank in the Laurels]

I don't know where I read it but the idea of counter balance to spin drift is left hand twist. The article's premice was that a .308 bullet at 1000 yards depending on velocity would drift to the right around 2-4 inches and that military snipers were already using left hand twist to off set the spin affect..it's just about the same amount, interesting...maybe it was on the snipers hide forum.. I didn't even know they made left twist barrels, maybe they are only offered to military use, don't know. I've spent most of my years shooting out to 500 yards and always blamed the shift of impact on winds not spin drift and it was usually an inch or so with PPC's or BR's...lighter slower bullets than the big 30's. Geeezzz now I got something else to think about...never ends !!

 

[Varmtr]

The only rifles that I know of that had left hand twist was the 303 Lee Enfield. Left hand twist unscrewing a barrel not likely it would actually tighten the barrel if any. Look down the rifle from the but end the twist rotates in the same direction as tightening the barrel into the action.
I would think wind drift would be more of a concern than coriollis and spin drift within 1000y maybe with a benchrest rail gun you might see some deflection.

 

[Bravo 4]

Frank,
None of our Sniper Weapon Systems have a lefty twist.
If you are talking about left spin drift canceling out the rightward Coriolis effect, that would only work in the northern hemisphere. Problem with that is that for most of our effective ranges Coriolis is such a small factor that no value is usually entered, so it wouldn't cancel out anything (none worth noting on a regular basis). I would rather they not mess with something like that as some of our weapons would be right and some left, better to have one standard or it could get confusing. Besides, we don't just operate in the northern hemisphere.

 

[J E Custom]

Rather than explain Coriolis effect and get into another debate I posted a link that will help explain.

Coriolis effect - WOW.com

My under standing is that it does not make any difference if a barrel is left hand rifled or right hand rifle the effect will still exist, only in a different direction. My understanding is That the direction you are shooting and north or south of the equator can make a difference in the amount.

There has always been the debate about right hand rifling loosening the barrel. If torqued correctly this will not happen. but if the barrel is installed hand tight it is very possible.

Many European countries believe in left hand twist for one reason or another and still use them.

There is no proof that a left hand twist is any more accurate than a right hand twist and with no difference is Coriolis effects except in another direction. (Important to the shooter that has a left hand twist to know).

The bottom line is that nether the Coriolis or twist direction make any difference to most shooters because of the distance they shoot.

Just my opinion

J E CUSTOM

 

[Frank in the Laurels]

I understand the n/s hemisphere difference, but it is an interesting idea or falicy, either way... Do any American barrel makers actually make a left twist barrel ??? Just curious..

 

[J E Custom]

I understand the n/s hemisphere difference, but it is an interesting idea or falicy, either way... Do any American barrel makers actually make a left twist barrel ??? Just curious..

I really don't know. There are many that probably could (The cut rifle guys) do the gain twist
barrels so I would assume they could cut a left hand twist if they wanted to. the Button rifle makers
would have to make many changes in machines and tooling, so I would not expect them to be interested.

With the direction of twist meaning very little or none, It appears that they elected to tool up for right hand twist only.

It is a very interesting topic and has been a good post. We sometimes make a mountain out of a mole hill and with the distance required to make Coriolis a consideration, it will only effect the extreme shots and needs to be taken into account for these distances no mater what the twist direction is.

The twist appears to be a personal choice and is the buyers call and no proof has been presented
that makes left hand twist any better. (I have a feeling that if it was we would all be shooting left hand twist). and all of the good barrel makers would be making them.

Just another opinion

J E CUSTOM

 

[ColoYooper]

Not huge numbers, but at 1000yards with a 300WinMag they are significant. The Coriolis effect will modify the point of impact here in the northern hemisphere at ~40deg latitude when shooting North to South and equally when shooting South to North. At 1000yards it will move the impact ~1/4 MOA to the right. Spindrift is double that at ~1/2 MOA to the right with a right hand twist barrel. Added together they move the bullet ~3/4 MOA to the right at 1000yards. If you had a Left hand twist, the net effect would be 1/4 MOA to the left. That is a 3x improvement!!!...although the effects of wind make it nearly impossible to observe.

I have 3 custom barrels built by Mark Chanlynn...(2) are .30 Caliber and (1) 6.5. The 30s are right hand twist, and the 6.5 is left hand twist. I asked Mark why he didn't make the 30s with a Left hand twist as well to counter spin drift with Coriolis. He smiled and said it was a trade secret! Then he showed me his antique barrel cutting machine which is configured to cut rifling on the front of the machine with right hand twist...he is tooled for 7mm and up. On the back side of the machine, with the left hand twist, he is tooled to cut calibers smaller than 7mm! NOTE: The cutting hooks are specifically right hand or left hand twist and are not interchangeable, and he's not seen the need to duplicate them.

 

[digger11]

The original Remington barrels for the 17 Rem were left hand twist.I don't even know why I know that. My head is filled with useless knowledge.

 

[Frank in the Laurels]

Learn sum-tin every day on here !!

 

[Bravo 4]

I received a PM about this Gunwerks video https://m.youtube.com/watch?v=jX7dcl_ERNs, and asked why I don't correct for Coriolis until past 1000 yards. I didn't want to respond with anything incorrect (and it also may inspire good conversation) so I am bringing it to the thread for everyone to see the responses.

My initial thought was: to start with they may be using the term "Coriolis effect" incorrectly in the video. I have been taught and so I believe that Coriolis effects the horizontal (right/left) displacement of a bullet's POI from it's intended, while the term Eotvos effect is what happens to it's vertical POI. So I don't associate vertical POI changes to Coriolis, only right and left.
Now as for what I consider Coriolis (right/left), it all depends on your latitude (distance from the equator). At 1000 yards, @ my approx 35 degree latitude, the difference in right impact (northern hemisphere) is less than one "click" on my 1/4 moa and 1/10 mil adjustments. At 1500 yards the difference shows to be a little more than that one "click" with the moa scopes and almost exactly 1/10 mil or one full "click" with my mil based scopes.
If I were to go "up" considerably on the map to say Ft. Severn, Ontario Canada to a latitude of about 56 degrees, then the values go up about 50%. So that almost 1/4 moa "click" @ 1000 becomes a "click", and the a little more than a 1/4 moa "click" becomes basically 1/2 moa @ 1500 yards.
To get these numbers I just sat down and punched different latitudes and azimuth of fire into my Ballistics app and turned on Coriolis. I put in 0 degrees like on the equator, 35 degrees for where I'm currently located and then 56 degrees for the top of Canada just to see the differences. On top of that I input 0, 90, 180, and 270 degrees azimuth of fire for each of these to account for the vertical as well. This, to me, is what most folks consider Coriolis and what I consider Coriolis and Eotvos. Maybe folks just combine the two to simplify, or I'm just flat out wrong!?