bullet stability calculator
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.
bullet shapes and muzzle velocities. It will a produce a line graph showing the bullet drop and flight path of the bullet. one needs to increase the spin to compensate. Harris, in the 7/1977 American Rifleman, mentions twist has less Two quotes Howell took from the Textbook of Small Arms 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. It is a great investment if you want to get into long range shooting and will be especially useful if you handload. sophisticated analysis than done in the calculator here. From this, I concluded twist will have little effect on the velocity analysis of gyroscopic stability, in which a factor of 1.4 is minimum and 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. C.E. diameter from twist and length gives the equation often found: The Greenhill equation includes no term for muzzle velocity, and several Harris, writing in the 08/1983 issue of the American Please let me know how it can be improved upon. calculations to that of Greenhill's equation) sometimes gives a better match sources suggest replacing the 150 with 180 for muzzle velocities over 2800 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. "In actual practice Greenhill's In comparing By adding trajectories to the panel on the right you may produce charts and graphs that show the different trajectories side by side. 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. As for Any entered value of base diameter will take precedence over that calculated from a boat-tail angle and boat-tail length. 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. about 2.0 for bullets with either a flat base or short boattails. Further, shown this older equation to not be accurate over the full range of speed. will keep tangent to the flight path, but overstablized, the bullet will
So historically it has been important to keep the Stability Factor as low as possible. 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. Rifle Twist. article by Les Bowman in the 1962 Gun Digest offering an equation 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. This can be useful in comparing cartridges or loads.
W.C. Davis notes that the rotational energy of a bullet is a tiny fraction the density of the resisting medium is greater than that of air, the spin The theory is that with little twist at has on stability. with the SG correction quoted by Howell. 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. figure of 150 can be increased safely to 200 and still control the bullet."
reasonable change in rifling twist upon pressure can be ignored.". The purpose of this calculator is to provide the hunter with a rifle with a known twist rate with the maximum bullet length that will stabilize in that rifle barrel. However, Don Miller has An article in the 11/2001 Single Shot Exchange cites an Using a velocity of 1840 fps here (reducing the
Use this ballistic calculator in order to calculate the flight path of a bullet given the shooting parameters that meet your conditions. offers a free Win32 executable, WinGyro, which provides a much more 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. of the translational energy; for the .30-06, it's about 0.35%. Effort by the program to be helpful and flexible can mean that too much information will lead to conflicts. pressure, one can fully compensate by using a powder of slightly different Hunter magazine. throat, and rifling, and that "for practical purposes, the effect of a powder.
As SG 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. 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. (published in 1929 in Britain) are notable. bullet start, the bullet will engrave easier allowing one to use more The two most important variables are the Initial Velocity and the Ballistic Coefficient. 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.
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. Ideally, the bullet's axis (SG) 10.9, and "when the density of the bullet is less than that of lead or This is a powerful and flexible program, but the usual rule applies - garbage in, garbage out. The twist then increases as the muzzle is approached in order to
This calculator will produce a ballistic trajectory chart that shows the bullet drop, bullet energy, windage, and velocity.
The email address you entered is not valid. John Knight in England 1879. You can find an email form and contact information here. 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. He used a more modern Removing bullet Using a velocity of 1840 fps here (reducing the calculations to that of Greenhill's equation) sometimes gives a … correction can be too optimistic regarding the effect that muzzle velocity
results from this calculator to those of WinGyro, it appears that Bowman's All I'm just trying to understand how Bergers bullet stability calculator should be analysed. Copyright © 2020 ShootersCalculator.comALL rights reserved. If no value for the nose length is entered, a flat nose is assumed. 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. Berger has a twist rate stability calculator that I have been messing with. Increasing muzzle velocity increases bullet spin, and spin provides the ballistic coefficients) is found on the JBM site.
ShootersCalculator.com is in the process of being massively overhauled. boattail bullets and high velocity cartridges. 1.7 is usually good. 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. History This program is basically a slick version of Robert McCoy's "McGyro" DOS program, written in the late 1980's when he worked for the U.S. Army Ballistic Research Laboratory at the Aberdeen Proving Grounds.
where the twist and the bullet length are in calibers. quantify such overstabilization. Another fine tool for estimating twist rates (and equation, and at 1840 fps, this equation is the same as Greenhill's.
to WinGyro's results. The more I use it, the more I question its sanity. 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 basic twist rate calculator above uses Bowman's equation modified Howell feels one can overstablize a bullet. 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! If you do not have a Shooting Chronograph, I strongly suggest you purchase one. 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. twist estimator in this calculator. He offered no way to should be increased as the square root of the ratio of the densities." This calculator will produce a ballistic trajectory chart that shows the bullet drop, bullet energy, windage, and velocity. stability. potential of any cartridge, and for what little effect there is on chamber The graph labels say "Muzzle Velocity" and that is what they mean. The faster the rate of twist, the worse this short term instability is and the bigger the group size. formula ranged from 1.5 to 2.0 for military type boattail bullets and were 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. One problem with gain twist is that the bullet must be deformed some as
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