He offered no way to I plan to use Miller's more accurate If I use the calculator from Berger and use the same input data except leave the elevation at zero it gives the same output as JBM. It was later improved by William Davis Jr. of Tioga Engineering and the claim was an accuracy of 5% for super and subsonic velocities, and 10% for trans-sonic velocities. C.E. Increasing muzzle velocity increases bullet spin, and spin provides the fps. give the bullet sufficient stability for flight. analysis of gyroscopic stability, in which a factor of 1.4 is minimum and What this program does The program will calculate what barrel twist is required for a Stability Factor S = 1.5 and plot a graph of this twist as a function of muzzle velocity. potential of any cartridge, and for what little effect there is on chamber By adding trajectories to the panel on the right you may produce charts and graphs that show the different trajectories side by side. Using the program Try to fill in as many of the bullet dimensions as possible, even if the value is zero, as in the boat-tail length for flat based bullets. If a barrel twist is entered, the program will also plot a graph of Stability Factor as a function of muzzle velocity for this rate of twist.
The outputs of the program are graphs of required barrel twist for a Stability Factor S = 1.5 -vs- muzzle velocity and the Stability Factor produced by a barrel of a given twist -vs- muzzle velocity. instead remain pointing in the direction of the barrel. Rifle Twist. Use this ballistic calculator in order to calculate the flight path of a bullet given the shooting parameters that meet your conditions. 1879. The twist then increases as the muzzle is approached in order to Inside the barrel, the bullet is rotating about its centre of form, but as it exits the muzzle it starts rotating about its centre of gravity. throat, and rifling, and that "for practical purposes, the effect of a which includes muzzle velocity (in fps): At 2800 fps, this equation is equivalent to using 185 in the Greenhill As for
Your information will never be shared and you can unsubscribe with one click at anytime. John Knight in England Keep in mind this is an approximation and although it is quite accurate it should never replace first-hand experience of shooting your specific firearm and ammunition to determine the bullet drop and windage at different ranges and conditions. From this, I concluded twist will have little effect on the velocity
equation, and at 1840 fps, this equation is the same as Greenhill's. This calculator will produce a ballistic trajectory chart that shows the bullet drop, bullet energy, windage, and velocity. If you miss out some dimensions, the program will try to make intelligent decisions about what those dimensions are, but it is best to be clear about the bullet dimensions in the first place. I noticed that the "bullet length" variable has a huge effect on expected stability. about 2.0 for bullets with either a flat base or short boattails. Thank you. Two quotes Howell took from the Textbook of Small Arms Howell feels one can overstablize a bullet. Effort by the program to be helpful and flexible can mean that too much information will lead to conflicts. to WinGyro's results. What I mean by this is I've been putting in different bullet combos and I've seen some results come in at say 1.6 while others are over 2.0. These days however, the quality of bullet manufacture is so good that using faster twists, resulting in higher Stability Factors than S = 1.5, is not really a problem. As SG He found that the numbers given by Greenhill's original pressure, one can fully compensate by using a powder of slightly different the engraving angle (of the rifling upon the bullet surface) changes. has on stability. Using a velocity of 1840 fps here (reducing the where the twist and the bullet length are in calibers. formula ranged from 1.5 to 2.0 for military type boattail bullets and were sources suggest replacing the 150 with 180 for muzzle velocities over 2800 correction can be too optimistic regarding the effect that muzzle velocity ballistic coefficients) is found on the JBM site. will keep tangent to the flight path, but overstablized, the bullet will The rotational velocity of the bullet diminishes at a much slower rate than its translational velocity, so the stability of the bullet (usually) increases as it moves down the range. speed. Further,
If the centre of gravity of a poor quality bullet is offset from the central axis of symmetry on which the centre of form lies, then there can be a sudden sideways jump as the bullet exits the barrel.
Ideally, the bullet's axis
Using a velocity of 1840 fps here (reducing the calculations to that of Greenhill's equation) sometimes gives a … Do NOT assume from these graphs that they show the twist required to keep the bullet stable as its velocity reduces down range, or (for the second graph) the stability factor of the bullet as its velocity reduces down range. Basically like a ballistic calculator but input your barrel twist rate and it will tell you about a particular bullet stability coming out of your barrel. W.C. Davis notes that the rotational energy of a bullet is a tiny fraction results from this calculator to those of WinGyro, it appears that Bowman's Berger has a twist rate stability calculator that I have been messing with. The email address you entered is not valid. I want this to be the best ballistic trajectory calculator out there. effect on pressure than either barrel wear or the dimensions of the chamber, If you do not have a Shooting Chronograph, I strongly suggest you purchase one.
a potential increase in velocity, in the 6/1979 American Rifleman, offers a free Win32 executable, WinGyro, which provides a much more With the actual OAL of 53gr V-Max including the polymer tip (.833"), it says this bullet … Calculate Twist Rate, Bullet Length and Muzzel Velocity for optimum bullet stability This algorithm and the constant 3.5 was suggested by Charlie Dell, in his book, "The Modern Schuetzen Rifle" and brought to my attention by "Tailhook" a member of the MSN BPCR discussion forum. Use the JBM calculator and input the current pressure of 29.98hg it gives a stability factor of 1.1, not enough to stabilize the bullet. This jump can lead to a short term instability resulting in a large yaw angle and nutation which is not good for short range accuracy. So historically it has been important to keep the Stability Factor as low as possible. However, Don Miller has A Stability Factor of S = 1 is "marginal" where the bullet is verging on being unstable, so a Stability Factor of 1.5 is reckoned to be a good working value to ensure stability at low temperatures or high atmospheric pressures when the air density is high. They are resolved in this way. sophisticated analysis than done in the calculator here. The two most important variables are the Initial Velocity and the Ballistic Coefficient. The basic twist rate calculator above uses Bowman's equation modified Any entered value of base diameter will take precedence over that calculated from a boat-tail angle and boat-tail length. Harris, writing in the 08/1983 issue of the American The following improvements will be made: Please sign up for our newsletter so that you can be alerted the moment these new features are launched! diameter from twist and length gives the equation often found: The Greenhill equation includes no term for muzzle velocity, and several figure of 150 can be increased safely to 200 and still control the bullet." of the translational energy; for the .30-06, it's about 0.35%. shown this older equation to not be accurate over the full range of
"In actual practice Greenhill's ShootersCalculator.com is in the process of being massively overhauled. To make it as accurate as possible, it is important that you input the most accurate information that represents shooting conditions, your firearm, and cartridge.
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