Twist rate & direction
- Thread starter Tugmanade
- Start date
Cheers, much appreciated
If you're looking for that information to enter it into a ballistic calculator, then don't bother
Unless you're shooting extreme long range (1000 yards plus) then twist rate and direction make absolutely no difference to the point of aim produced by the ballistic calculator
Cheers
Bruce
Unless you're shooting extreme long range (1000 yards plus) then twist rate and direction make absolutely no difference to the point of aim produced by the ballistic calculator
Cheers
Bruce
For the Zulus to give you an accurate point of aim when using the ballistic calculator, you only need to give it the following information:
a. The distance you zeroed at
b. The scope height above the bore (from the centre of the objective lens to the centre of the bore)
c. Muzzle velocity (if you have access to a chronograph then use the chrono figures rather than anything printed on an ammo box)
d. Ballistic coefficient
Given the terrain and weather in the UK, neither altitude, temperature or air pressure will make any noticeable difference to the calculation
Bullet weight and length only become relevant for windage calculations and the Zulus doesn't do wind holds
If you find the find the POA produced by the Zulus results in a POI that's higher or lower than the calculated POA then try the following:
for short range errors (sub 12ftlb air rifle ranges) change the scope height and/or BC
For longer range errors, change muzzle velocity
For example, on my 22 rimfire zeroed at 50 yards, my POA at 100 yards resulted in a POI that was high
That means the ballistic calculator thought the bullet would drop more than it actually did and so produced a POA that was lower than it should have been
So, to get the ballistic calculator to give a POA closer to the POI, I increased the muzzle velocity by 20fps and tired again
The POI was still higher than the POA, but closer than before, and another adjustment of 10fps got the POA and POI to be the same
I went through the same process of the POI being above the POA and tried to get them to match by changing the ballistic coefficient
That basically was a waste of time. I discovered that changes in BC have much less effect 0n POA than changes in muzzle velocity at longer ranges
Cheers
Bruce
a. The distance you zeroed at
b. The scope height above the bore (from the centre of the objective lens to the centre of the bore)
c. Muzzle velocity (if you have access to a chronograph then use the chrono figures rather than anything printed on an ammo box)
d. Ballistic coefficient
Given the terrain and weather in the UK, neither altitude, temperature or air pressure will make any noticeable difference to the calculation
Bullet weight and length only become relevant for windage calculations and the Zulus doesn't do wind holds
If you find the find the POA produced by the Zulus results in a POI that's higher or lower than the calculated POA then try the following:
for short range errors (sub 12ftlb air rifle ranges) change the scope height and/or BC
For longer range errors, change muzzle velocity
For example, on my 22 rimfire zeroed at 50 yards, my POA at 100 yards resulted in a POI that was high
That means the ballistic calculator thought the bullet would drop more than it actually did and so produced a POA that was lower than it should have been
So, to get the ballistic calculator to give a POA closer to the POI, I increased the muzzle velocity by 20fps and tired again
The POI was still higher than the POA, but closer than before, and another adjustment of 10fps got the POA and POI to be the same
I went through the same process of the POI being above the POA and tried to get them to match by changing the ballistic coefficient
That basically was a waste of time. I discovered that changes in BC have much less effect 0n POA than changes in muzzle velocity at longer ranges
Cheers
Bruce
Cheers Bruce,
I’ve got it on a .17 at the moment, but it’s my intention to swap it between that & my .22 once I’m a bit more familiar with it all.
Very much appreciated
Ade
trickie
Well-Known Member
What Bruce said, is also what my finding (with help to be fully open). On my ballistic calculator there is an option to “true”.
For me that ment zeroed at 100, spot on. At 300 I was 3 clicks high. Truing allowed me the enter the correct elevation from zero save and update, job done.
If you don’t have Strelok already, it’s no longer in the app stores sadly.
For me that ment zeroed at 100, spot on. At 300 I was 3 clicks high. Truing allowed me the enter the correct elevation from zero save and update, job done.
If you don’t have Strelok already, it’s no longer in the app stores sadly.
It's a right hand twist. Trust me, if you had a left hand twist, you'd know. The cleaning brushes will unwind themselves off the cleaning rod if you're not paying attention, with a left hand twist barrel. AMHIK...
Yes, I have one rifle with a left hand gain twist barrel.
Yes, I have one rifle with a left hand gain twist barrel.
Bavarianbrit
Well-Known Member
Does gain twist give better accuracy than constant twist rifling? Then again does left vs right twist rifling affect accuracy.
The meaning of life.
Tin of worms just opened.
The meaning of life.
Tin of worms just opened.
Given that you've just mentioned the dreaded words "left vs right", there's a high chance this thread will be moved to the Political Discussion section ere long....
palmer_mike
Well-Known Member
Sounds like a marketing gimmick to me?
Barrels on double rifles are generally regulated to converge at a certain distance, which would do exactly the same thing. Also double rifles are normally regulated at a much shorter range than that at which transposed rifling would have any real effect?
Bavarianbrit
Well-Known Member
Does the earths rotation play a role? Asking for a sniper friend. 
Yes...and no. Does a gain twist give greater accuracy? No, not really (all things being equal). Does a gain twist give better accuracy across a wider range weight of bullets? Absolutely. Especially with long-for-caliber chamberings.
The simple explanation is that there is less bullet deformation as the bullet goes into the throat. With longer bullets, jackets can bulge/separate and allow pockets to form as the bullet is pushed down the barrel (and back down into the caliber diameter). Ideally, rotation of the bullet should negate this, but it doesn't, especially at longer ranges where RPM's begin to slow, making the bullet "less stable". Since the twist rate of the rifle and the throat of a chamber is typically set up for a specific weight of bullet (or more accurately, a bullet length), a chamber tends to operate best with a certain weight of bullet. (140gr for 6.5CM for example) But when a shooter puts a faster twist barrel to shoot longer bullets, they reach a point where it's no longer about stability. or more accurately, there are diminishing returns on shooting longer bullets beyond the normal loss of velocity. Accuracy becomes non-linear at long range. It is believed (based on Doppler radar chronograph testing) that the bullet begins to get deformed when a length-to-twist ratio is exceeded (demonstrated by the observation of coefficients being different; essentially the shape of the bullet itself is being changed).
Sooooo....gain twist barrels allow you to "ease" the bullet into the rifling at a slower twist rate, and then drive the twist rate faster as it goes down the barrel, giving it the stability it needs when exiting the barrel (which is kind of the inverse of swaged barrels, when you think about it...but I digress).
As to left hand twist. The primary benefit, regardless of which hemisphere you shoot in, is that for a right handed shooter, a left hand twist causes the rifle to recoil into your body, and not away from your body. This makes managing recoil, as the bullet goes down the barrel, much more consistent.
John Pope knew this, and was why all his Schutzen rifles were equipped with lefthand twist barrels (primarily because the offhand/standing position is so unstable, the consistent recoil management was a huge benefit). It was only the advent of modern geared drilling machinery that pushed left hand twist rifles into obscurity (they only cut in a clockwise motion). Otherwise, they probably would have become the norm for rifles, as that was what most competition shooters used at the time.
Back to the gain twist question. With modern gain twists, a lot of experimenting has been done, and anecdotal evidence collected. Current wisdom is that a gain twist should be no more the 1/2-3/4 a twist. Any more than that and it causes other issues (pressure spikes, reduced velocities, requires non-practical length barrels, etc.). The other observation was that gain twist barrels tend to show a high level of accuracy across a greater variety of bullet weights. The thought being, because (again) bullet deformation isn't playing a factor (or as much of one) on accuracy.
Anyways, sorry for the long winded response, but felt the need to expound on this topic before all the naysayers come in and say it's a fad or immaterial.
Is it worth the additional cost to get a LH twist or GT today? Probably not for most. But, that being said, there used to be only one company that offered LHGT barrels (Bartlein). As I understand it, there are two others that are either offering them, or planning to offer them. And if that happens, prices will most likely fall significantly, with only a small upcharge due to the vendor having to increase the stock kept on hand (due the variety of GT/LH/caliber combinations).
Anyways, HTH some....
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Bavarianbrit
Well-Known Member
Magic, many thanks for this considered reply.
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