338 lapua twist rate


  • Best .338 Lapua Rifles [2021]
  • Lapua Ballistics Tips: Stability Estimation
  • THE TUBB 33XC, 37XC & 41XC CARTRIDGES BY DAVID TUBB
  • Twist Rate Stability Calculator
  • What do you mean by faster and slower twist rate?
  • Best .338 Lapua Rifles [2021]

    Stability is affected by several factors, the most important factors being barrel twist rate and the length of the projectile. To a lesser degree it is also affected by the bullet shape, velocity and environmental conditions.

    You can estimate bullet stability during the flight path with the stability estimator function in Lapua Ballistics. In this article, we will explain bullet stability to a high detail and how to use Lapua Ballistics as a tool to understand it. What is barrel twist rate? Twist rate is defined as the length of one full turn of the bullet degrees in inches or millimeters in the barrel. You can measure the twist rate of your rifle barrel by marking e.

    Make sure that the cleaning rod follows exactly the lands in the barrel. What happens if the bullet is too long compared to the twist rate? If the bullet is too long compared to the twist rate, it will be unstable and may start to wobble or even turn completely crosswise. An overstabilized projectile does not follow exactly the trajectory of the curved flight path but flies slightly nose up.

    Technically speaking, the axis of the bullet does not follow the tangent of the trajectory. This increases the air drag and shortens the flight range. An unnecessary high rotation speed also intensifies the adverse effect of smaller shape and symmetry defects of the projectile. How to increase bullet stability The stability of a bullet can be increased by the following factors roughly in the order of importance : Tighter shorter twist rate of the barrel Shorter bullet High altitude lower air density High temperature lower air density Low air pressure lower air density High humidity lower air density.

    Yes, water vapor is less dense than air! Lower air density means less aerodynamic forces affecting the bullet so it remains stable easier. Stability estimation — the theory Traditionally, bullet stability is estimated by using quite simple equations like the Miller and Greenhill equations. The value of the stability calculator is more in comparing different combinations with each other twist rate, bullet to be used, muzzle velocity, environmental conditions, etc. Gyroscopic stability Sg means the ability of a rotating object to resist the change of its rotating axis.

    Sg is quite easy to calculate and its value at the muzzle has to be absolutely over 1. In practice some safety margin is needed there so the recommended minimum value is 1. Values clearly over 2. Dynamic stability Sd means the ability of the bullet to decrease a wobbling motion caused by an internal or external effect.

    Sd is much more difficult to evaluate than Sg and it needs 6 DOF calculations. Lapua Ballistics is one of the very few ballistics software solutions that is capable of utilizing this and possibly the only one completely free of charge. Most software are capable of estimating stability only by Sg which is usually reasonable good enough for short distances but not to long distances and to the transonic region — where Sd is the main factor for stability.

    The vertical axis of the stability curve expresses Sg and the horizontal axis Sd. The favorable stability region is expressed as light blue but high quality bullets often retain the stability also in the dark blue region. Dynamic stability is affected by e. The distance between cm and cp is very important because it defines the aerodynamic moment vector that tries to turn the bullet crosswise. Air density is also important, the stability is better in a higher altitude and warm weather.

    The grooves made by the lands in the barrel on the bullet surface slightly affect the dynamic stability and decelerate the rotating speed faster compared to a smooth surface.

    Dynamic stability is usually the problem only at long distances and in the transonic region. The bullet can fly — and often does — fly stable and accurate also far inside the dark blue region. How to read the stability calculator in Lapua Ballistics Simple guide for ensuring bullet stability The target for the gyroscopic stability value Sg at the muzzle is between 1.

    Never go below 1. This is a good guide for both short range and long range bullets. The stability curve should turn as late as possible no. If the curve turns 90 degrees to the left it means a higher risk of unstability than if the curve turns only 45 degrees to the left. The stability curve of high BC long range bullets always turn clearly to the left.

    Shorter projectiles tackle this problem easier but on the other hand they reach the transonic region earlier because of a lower BC. Transonic region stability can be improved by a tighter twist rate but this may have other undesired effects to the accuracy in general. Example of bullet stability estimation in Lapua Ballistics: Gyroscopic stability Sg is expressed on the y-axis 0 — 5. The safe stability region is expressed as a light blue area.

    Only the bullet ability to correct external disturbances e. Gyroscopic stability increases with the distance here 1. Effect of twist rate in. Gyroscopic stability at the muzzle is too low first red dot ca. There is a high risk for the bullet to be unstable already at the muzzle. Gyroscopic stability at the muzzle first blue dot is good, ca 1.

    The bullet has good presumption to fly stable and accurate to long ranges. Gyroscopic stability at the muzzle beginning of gray curve is slightly too high, ca. But the bullet is spinning unnecessary fast and may be susceptible to adverse effects of small imperfections in shape or symmetry. A good combination, but maybe not the optimal one. The exact Sg and Sd values can be seen in the trajectory table if Sg and Sd are selected as columns to be visible.

    Please note that the software may calculate the stability values for longer distances than the shooting distance so the last marker may not be the actual shooting distance. This feature is available only for Lapua bullets and cartridges because the details of bullet structures e. Gyroscopic stability at the muzzle is too low first red dot , ca.

    This combination is known to be in the limit of appropriate function — sometimes it works, but usually not. Gyroscopic stability at the muzzle first blue dot is good, ca. It is typical for all long high B. How bullet length affects the stability In this graph you can see the effect of bullet length to gyroscopic and dynamic stability in a. The shorter gr GB Scenar red graph retains its stability better than longer gr GB Scenar blue graph , but reaches the transonic region a little earlier than the ballistically better gr bullet.

    You can compare differences in bullet velocity and energy in their respective graphs and trajectory table. If you can see a clear wave pattern in the trajectory curves, it is also an indication of potential instability.

    In this case, shoot paper targets to check that the holes are round and the accuracy is good enough for your purpose. Extreme examples In this graph you can see two.

    Even if the gyroscopic stability is dangerously low in the beginning ca. This combination is in practise a well-proven small game cartridge. The 69 gr Scenar bullet blue curve is much too long for this twist rate. Gyroscopic stability starts from a very low value and also the dynamic stability starts to weaken significantly immediately.

    In this case the projectile reaches the transonic area at the distance of m. Stability will revert soon after that and the bullet likely continues a stable flight without a loss of accuracy. This is also helped by the high gyroscopic stability value of over 3. Lapua Ballistics 6 DOF is the only free of charge consumer software capable for these kind of studies.

    For those interested to understand the theory behind bullet stability even further, we recommend the following reading: McCoy, R. Studies on Unmanned Atmospheric Flight. Doctoral Thesis. Aalto-University, Helsinki, Finland. Our next tip will feature the use of spin drift adjustment. Stay tuned!

    Lapua Ballistics Tips: Stability Estimation

    Not only is it preferred for snipers, but also some hunters and civilian competitive shooters. Its effective range is around 1, yards; which is why I recommend it for competitive target practice and hunting. In , this caliber established a new record for the longest recorded sniper kill from a distance of 2, yards.

    How to Choose the Best. Barrel Length Considerations Longer barrels tend to give superior muzzle velocity. The more muzzle velocity, the better the range and the more predictable trajectory the bullet will take. A predictable trajectory is shoptalk for a flat trajectory or a more accurate shot. However, long barrels will add more weight to your rifle. While this may not always be an issue in various tactical situations, I find it somewhat inconvenient when hunting.

    After all, hunting is all about being mobile and being able to stalk your prey. Recoil Rifles that take the. If you like stealth hunting and believe a sniper rifle is for you, then a Lapua rifle may serve you well.

    For one thing, it has a heck of a recoil. The recoil from a. Match Grade Triggers A match grade trigger is also something to keep an eye out for. Of course, two-stage triggers will also help improve your accuracy and control over the weapon.

    While this provides tons of use in tactical situations, also keep in mind the potential hunting applications of a higher rifle capacity. You want to be able to fire at least two or three quick shots in succession even on bolt action rifles. Which is why I know that the ability to fire more shots in a short amount of time can be important, not to mention satisfying.

    Shooting a. These rifles, and this ammo, were designed to stop terrorists from over a mile away. Some Lapua rifles may come with factory-mounted optics. But I will say that more often than not, you can get more from an aftermarket scope.

    You can also save some money by getting a rifle without optics but with multiple mounting options. The Twist The recommended minimum twist rate for. The twist rate is a measure of the spin that the bullet endures while blasting out of the barrel. Because of the unique specifications of. But make no mistake. However, I remember a while back when I avoided buying. Granted, the latter is a known game round that many hunters use.

    That said, after some testing I realized that this round is the far superior one. Their high-end performance deserves a premium price tag. Between the insane distance, tremendous accuracy, and reliable stopping power, you have to at least try and shoot a few. You can also try. Another common matchup is. Also, though some sources suggest that a.

    Other Considerations There are tons of. While these rifles are excellent choices for most gun owners, there are other options for higher budgets and different needs.

    Each of the following rifles has great stopping power and a variety of features that make them safe to handle and effective on the long-distance gun range.

    THE TUBB 33XC, 37XC & 41XC CARTRIDGES BY DAVID TUBB

    The stability curve of high BC long range bullets always turn clearly to the left.

    Twist Rate Stability Calculator

    Shorter projectiles tackle this problem easier but on the other hand they reach the transonic region earlier because of a lower BC. Transonic region stability can be improved by a tighter twist rate but this may have other undesired effects to the accuracy in general. Example of bullet stability estimation in Lapua Ballistics: Gyroscopic stability Sg is expressed on the y-axis 0 — 5. The safe stability region is expressed as a light blue area.

    Only the bullet ability to correct external disturbances e. Gyroscopic stability increases with the distance here 1. Effect of twist rate in. Gyroscopic stability at the muzzle is too low first red dot ca. There is a high risk for the bullet to be unstable already at the muzzle. Gyroscopic stability at the muzzle first blue dot is good, ca 1.

    The bullet has good presumption to fly stable and accurate to long ranges. Gyroscopic stability at the muzzle beginning of gray curve is slightly too high, ca. But the bullet is spinning unnecessary fast and may be susceptible to adverse effects of small imperfections in shape or symmetry. A good combination, but maybe not the optimal one. The exact Sg and Sd values can be seen in the trajectory table if Sg and Sd are selected as columns to be visible.

    Please note that the software may calculate the stability values for longer distances than the shooting distance so the last marker may not be the actual shooting distance. This feature is available only for Lapua bullets and cartridges because the details of bullet structures e. Gyroscopic stability at the muzzle is too low first red dotca. This combination is known to be in the limit of appropriate function — sometimes it works, but usually not.

    Gyroscopic stability at the muzzle first blue dot is good, ca. It is typical for all long high B. How bullet length affects the stability In this graph you can see the effect of bullet length to gyroscopic and dynamic stability in a. The shorter gr GB Scenar red graph retains its stability better than longer gr GB Scenar blue graphbut reaches the transonic region a little earlier than the ballistically better gr bullet.

    You can compare differences in bullet velocity and energy in their respective graphs and trajectory table. If you can see a clear wave pattern in the trajectory curves, it is also an indication of potential instability. In this case, shoot paper targets to check that the holes are round and the accuracy is good enough for your purpose. Extreme examples In this graph you can see two. Even if the gyroscopic stability is dangerously low in the beginning ca.

    This combination is in practise a well-proven small game cartridge. The 69 gr Scenar bullet blue curve is much too long for this twist rate. Gyroscopic stability starts from a very low value and also the dynamic stability starts to weaken significantly immediately. In this case the projectile reaches the transonic area at the distance of m. Stability will revert soon after that and the bullet likely continues a stable flight without a loss of accuracy.

    This is also helped by the high gyroscopic stability value pkgi ps3 download over 3. Lapua Ballistics 6 DOF is the only free of charge consumer software capable for these kind of studies. For those interested to understand the theory behind bullet stability even further, we recommend the following reading: McCoy, R. Studies on Unmanned Atmospheric Flight. Doctoral Thesis. Aalto-University, Helsinki, Finland.

    Our next tip will feature the use of spin drift adjustment. The rubber pad is fairly hard and appears as if it will hold up over time and it is also textured to provide good grip allowing it to stay in place nicely during use.

    The butt of the stock is adjustable in more ways than I have seen before on a tactical rifle. Sako has taken some of the features from their target rifles and applied them to the TRG and that is evident here.

    While most of the adjustments are not easily done in the field since they require spacers and disassembling the various components, it is none the less adjustable in many different ways.

    The buttplate is not only adjustable for length of pull, but it also moves up and down, left and right, rotates clockwise or counter clockwise, and even pivots left and right.

    What do you mean by faster and slower twist rate?

    To adjust the buttplate in some of these directions will require purchasing some special spacers and new screws, but the rifle can be custom fit to any shooter.

    The cheekpiece is elevated above the standard comb of the stock to help place the shooters eye in line with the scope. There is also a taper toward the front that is there to allow the bolt to be easily removed without hitting the stock. The cheekpiece has a fairly sharp peek that is not the most comfortable especially over prolonged shooting with the Lapua.

    A padded eagle of tacops cheekpiece can help here. That steep peak does help the shooter maintain a solid cheekweld without slipping as the cheekbone seems to rest well on it. The cheekpiece is also adjustable in both left and right as well as elevation to again help the operator get the correct eye alignment. Though to adjust the cheekpiece in elevation, spacers are again required.

    While using spacers does take more time and energy to adjust and get it right, it does provide a solid nonmoving adjustment that only needs to be set once and will not move again until the operator wants it to.

    There is a butthook at the bottom rear of the stock that allows the shooter the flexibility of using a sandsock, holding the rifle with their off hand, or doing both. The pistol grip on the stock is a vertical grip that is nicely contoured to fit the shooting hand including a grooved area for the trigger finger.

    The grip is fairly wide with just a hint of a palm swell. The stock is ambidextrous and can be fired both left and right handed. One of our shooters is a lefty and he had no problems using the rifle shooting LH. See bottom picture on this page. Where the action rests in the stock it is wide and provides a solid mount for that action and this is evident if one looks in the tang area at the rear of the action, that width of the stock is carried all the way forward from the action up to the forearm.

    The stock is built solid and appears designed from the outset to handle the heavy magnum cartridges. The forearm on the stock is very flat which normally can be a problem from mounting a bipod, but in this case we purchased the matching Sako bipod that is designed for this rifle, more on that later.

    The flat forearm is great for firing from sandbags or similar types of rests and there is a gradual elevation taper going from the rear moving forward. This is ideal for applying slight elevation changes when shooting from bags. The forearm itself appears to be fairly short, but in reality it is normal length and perhaps just looks short when compared to the longer than average barrel.

    There is also an accessory rail on the bottom side of the forearm to allow the attaching of other accessories to the rifle. Overall the stock design is solid with many different adjustment options available to get the rifle to fit the user perfectly. It has a decent textured finish and the quality is very good. It also has the built in bipod mount, when using the matching Sako bipod, and the target rifle heritage is evident in the design.

    The stock also incorporates a unique chassis system design that provides a very durable mounting area for the action and also incorporates an accessory mount on the left side of the stock in front of the scope.

    The large Sako TRG action is cold hammer forged from a steel alloy that Sako claims provides added strength. The action certainly feels and looks solid and appears to be finely crafted. The TRG actions actually mount to what Sako calls an aluminum profile, or a chassis that the synthetic forearm and buttstock then attach to. This aluminum profile runs the entire length of the forearm and the action actually mounts to it using three good sized action screws, instead of the more common two, and these screws solidly mount everything together.

    The action has a hex style profile on top with a smaller closed ejection port. Actions with an ejection port make it more difficult to reach in with a finger to discreetly eject brass when desired, but it does allow for additional strength in the action. The TRG action is also drilled and tapped for attaching a picatinny rail and it also has a 17mm dovetail, with recoil stops, which can also be used for mounting sights. Just in front of the bolt on the right hand side of the action is the bolt release which easily allows the removal of the bolt.

    The bolt itself has a large bolt handle for easy gripping with gloved hands as well as adding additional leverage if needed. The bolt has three locking lugs, instead of two, which allows for a short 60 degree bolt throw, aiding in rapid bolt cycling.

    This extractor is a good compact design with positive extraction and ejection. At the rear of the bolt is a cocking indicator as well that protrudes when the bolt is cocked and ready to fire. The protrusion has a red stripe on it and it is visible in some of the pictures on this page.

    The entire bolt is finished in matte black bluing regardless of whether the rifle has the matte bluing or phosphate finish. The trigger guard is oversized to allow easy access with gloved fingers and the safety is a smaller protruding lever directly in front of the trigger inside of the trigger guard.

    If the safety is pulled to the rear it places the trigger mechanism in safe and it also locks the bolt. The operator needs to just simply flip the safety forward with his or her trigger finger and the rifle is then ready to fire.


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