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Values entered for the local atmospheric pressure (anything other than 29.92 in. I plan to use Miller's more accurate decreases, the gyroscopic inertia of the bullet decreases in proportion, and will keep tangent to the flight path, but overstablized, the bullet will where the twist and the bullet length are in calibers. the density of the resisting medium is greater than that of air, the spin The classic equation is for solid, lead alloy bullets of specific gravity 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. 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. Hg) will take precedence over local pressures estimated from the barometric pressure and the altitude. He offered no way to He mentioned Greenhill's work began with cannons in 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. By adding trajectories to the panel on the right you may produce charts and graphs that show the different trajectories side by side. 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! It is a great investment if you want to get into long range shooting and will be especially useful if you handload. should be increased as the square root of the ratio of the densities." Effort by the program to be helpful and flexible can mean that too much information will lead to conflicts. Ken Howell wrote about twist rate in the 07/1999 issue of Varmint one needs to increase the spin to compensate. a potential increase in velocity, in the 6/1979 American Rifleman, about 2.0 for bullets with either a flat base or short boattails. 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. offers a free Win32 executable, WinGyro, which provides a much more 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. Harris, in the 7/1977 American Rifleman, mentions twist has less Use this ballistic calculator in order to calculate the flight path of a bullet given the shooting parameters that meet your conditions. potential of any cartridge, and for what little effect there is on chamber correction can be too optimistic regarding the effect that muzzle velocity 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. Use this ballistic calculator in order to calculate the flight path of a bullet given the shooting parameters that meet your conditions. This calculator will produce a ballistic trajectory chart that shows the bullet drop, bullet energy, windage, and velocity. calculations to that of Greenhill's equation) sometimes gives a better match The more I use it, the more I question its sanity. 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. If you do not have a Shooting Chronograph, I strongly suggest you purchase one. Using a velocity of 1840 fps here (reducing the calculations to that of Greenhill's equation) sometimes gives a … equation, and at 1840 fps, this equation is the same as Greenhill's. Further, 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. The theory is that with little twist at figure of 150 can be increased safely to 200 and still control the bullet." READ THE TEXT AT THE BOTTOM OF THE PAGE TO ENSURE YOU GET USEFUL RESULTS. ballistic coefficients) is found on the JBM site. Removing bullet Copyright © 2020 ShootersCalculator.comALL rights reserved. formula ranged from 1.5 to 2.0 for military type boattail bullets and were results from this calculator to those of WinGyro, it appears that Bowman's to WinGyro's results. Thank you. This calculator will produce a ballistic trajectory chart that shows the bullet drop, bullet energy, windage, and velocity. This is a powerful and flexible program, but the usual rule applies - garbage in, garbage out. If no value for the nose length is entered, a flat nose is assumed. shown this older equation to not be accurate over the full range of Gain twist is a recurring fad. He used a more modern of the translational energy; for the .30-06, it's about 0.35%. instead remain pointing in the direction of the barrel. ShootersCalculator.com is in the process of being massively overhauled. diameter from twist and length gives the equation often found: The Greenhill equation includes no term for muzzle velocity, and several 1879. twist estimator in this calculator. stability. 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. Rifle Twist. With the actual OAL of 53gr V-Max including the polymer tip (.833"), it says this bullet … Using a velocity of 1840 fps here (reducing the Harris, writing in the 08/1983 issue of the American They are resolved in this way. Rifleman, noted Greenhill's formula was developed before spitzer article by Les Bowman in the 1962 Gun Digest offering an equation The graph labels say "Muzzle Velocity" and that is what they mean. 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. As SG (SG) 10.9, and "when the density of the bullet is less than that of lead or Ideally, the bullet's axis From this, I concluded twist will have little effect on the velocity One problem with gain twist is that the bullet must be deformed some as boattail bullets and high velocity cartridges. 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. "In actual practice Greenhill's analysis of gyroscopic stability, in which a factor of 1.4 is minimum and give the bullet sufficient stability for flight. In comparing results from this calculator to those of WinGyro, it appears that Bowman's correction can be too optimistic regarding the effect that muzzle velocity has on stability. An article in the 11/2001 Single Shot Exchange cites an Berger has a twist rate stability calculator that I have been messing with. powder. 1.7 is usually good. C.E. has on stability. The email address you entered is not valid. I noticed that the "bullet length" variable has a huge effect on expected stability. The two most important variables are the Initial Velocity and the Ballistic Coefficient. Please let me know how it can be improved upon. 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. throat, and rifling, and that "for practical purposes, the effect of a However, Don Miller has This can be useful in comparing cartridges or loads. 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. Any entered value of base diameter will take precedence over that calculated from a boat-tail angle and boat-tail length. the engraving angle (of the rifling upon the bullet surface) changes. fps. It will a produce a line graph showing the bullet drop and flight path of the bullet. Also computed is the G1 and G7 Ballistic Coefficients for a range of Mach numbers, and the barrel twists required for a Stability Factor 1.5 for a range of muzzle velocities. bullet start, the bullet will engrave easier allowing one to use more Technical 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. So historically it has been important to keep the Stability Factor as low as possible. You can find an email form and contact information here. He found that the numbers given by Greenhill's original 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. All I'm just trying to understand how Bergers bullet stability calculator should be analysed. with the SG correction quoted by Howell. quantify such overstabilization. In comparing

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