The Coriolis Effect comes into play with extreme long-range shots like this. The rotation of the earth actually moves the target a small distance (in space) during the course of the bullet’s flight. Photo by Dustin Ellermann at Whittington Center Range.
When you’re out at the range, the Earth seems very stable. But it is actually a big sphere zooming through space while spinning around its axis, one complete turn every 24 hours. The rotation of the earth can create problems for extreme long-range shooters. During extended bullet flight times, the rotation of the planet causes an apparent deflection of the bullet path over very long distances. This is the ballistics manifestation of the Coriolis Effect.
Bryan Litz of Applied Ballistics has produced a short video that explains the Coriolis Effect. Bryan notes that Coriolis is “a very subtle effect. People like to make more of it than it is because it seems mysterious.” In most common shooting situations inside 1K, Coriolis is not important. At 1000 yards, the Effect represents less than one click (for most cartridge types). Even well past 1000 yards, in windy conditions, the Coriolis Effect may well be “lost in the noise”. But in very calm conditions, when shooting at extreme ranges, Bryan says you can benefit from adjusting your ballistics solution for Coriolis.
Bryan explains: “The Coriolis Effect… has to do with the spin of the earth. You are basically shooting from one point to another on a rotating sphere, in an inertial reference frame. The consequence of that is that, if the flight time of the bullet gets significantly long, the bullet can have an apparent drift from its intended target. The amount [of apparent drift] is very small — it depends on your latitude and azimuth of fire on the planet.”
Coriolis is a very subtle effect. With typical bullet BCs and velocities, you must get to at least 1000 yards before Coriolis amounts to even one click. Accordingly, Bryan advises: “Coriolis Effect is NOT something to think about on moving targets, it is NOT something to think about in high, uncertain wind environments because there are variables that are dominating your uncertainty picture, and the Coriolis will distract you more than the correction is worth.”
“Where you could think about Coriolis, and have it be a major impact on your hit percentage, is if you are shooting at extended range, at relatively small targets, in low-wind conditions. Where you know your muzzle velocity and BC very well, [and there are] pristine conditions, that’s where you’re going to see Coriolis creep in. You’ll receive more refinement and accuracy in your ballistics solutions if you account for Coriolis on those types of shots. But in most practical long-range shooting situations, Coriolis is NOT important. What IS important is to understand is when you should think about it and when you shouldn’t, i.e. when applying it will matter and when it won’t.”
The Coriolis Effect — General Physics
The Coriolis Effect is the apparent deflection of moving objects when the motion is described relative to a rotating reference frame. The Coriolis force acts in a direction perpendicular to the rotation axis and to the velocity of the body in the rotating frame and is proportional to the object’s speed in the rotating frame.
A commonly encountered rotating reference frame is the Earth. The Coriolis effect is caused by the rotation of the Earth and the inertia of the mass experiencing the effect. Because the Earth completes only one rotation per day, the Coriolis force is quite small, and its effects generally become noticeable only for motions occurring over large distances and long periods of time. This force causes moving objects on the surface of the Earth to be deflected to the right (with respect to the direction of travel) in the Northern Hemisphere and to the left in the Southern Hemisphere. The horizontal deflection effect is greater near the poles and smallest at the equator, since the rate of change in the diameter of the circles of latitude when travelling north or south, increases the closer the object is to the poles. (Source: Wikipedia)
Butch Lambert of ShadeTree Engineering provided this tip. Butch notes that many 6 PPC benchrest group shooters also enjoy shooting in score matches. But to be really competitive in the BR for score game, that means shooting a 30BR, which has a wider, .308-class rim (0.4728″ diameter). Likewise, if you want to compete in 600-yard registered BR events or in varmint matches, you probably want to run a bigger case, such as the 6BR, 6mm Dasher, or 6-6.5×47. Those cartridges also have the larger 0.4728″ rims.
To convert a PPC-boltface action to shoot the bigger cases you can spend a ton of money and buy a new bolt. That can cost hundreds of dollars. The simpler solution is to turn down the diameter of the larger cases on a lathe. Butch explains: “We’ve seen plenty of interest in rebating case rims. This lets you shoot a 30BR in score matches using your PPC action. All you need is a new barrel. This saves buying another bolt, receiver, or rifle if you have a PPC boltface. Anyone who has access to a lathe can do this job pretty easily. Yesterday I turned 150 case in about an hour.” Below are photos of a rebated 6BR case, along with the lathe form tool Butch uses to rebate the case rims.
Readers who have just recently discovered the Daily Bulletin may not realize that AccurateShooter.com has hundreds of reference articles in our archives. These authoritative articles are divided into mutiple categories, so you can easily view stories by topic (such as competition, tactical, rimfire, optics, shooting skills etc.). One of the most popular categories is our Technical Articles Collection. On a handy index page (with thumbnails for every story), you’ll find over 120 articles covering technical and gunsmithing topics. These articles can help you with major projects (such as stock painting), and they can also help you build more accurate ammo. Here are five popular selections from our Technical Articles archive.
Stress-Free Pillar Bedding. Richard Franklin explains how to do a top-quality bedding job, start to finish.
OnTarget Software Review. Our Editors test free software that measures shot groups with great precision. We explain how to use the program and configure advanced features.
Savage Action Tuning. Top F-TR shooter Stan Pate explains how to enhance the performance of your Savage rifle by optimizing the torque settings of the action screws.
Complete Precision Case Prep. Jake Gottfredson covers the complete case prep process, including brass weight sorting, case trimming, primer pocket uniforming, neck-sizing, and, case-neck turning.
Stock Painting Instructions. Step-by-step guide for stock painting by expert Mike Ricklefs. Mike shows both simple coverage and fancy effects.
Winchester Repeating Arms has issued a Safety Notice and Recall for Winchester XPR rifles. This large-scale recall covers all XPR rifles, of all calibers. The issue involves the possibility of an unintentional discharge when the safety is manipulated. According to Winchester, continuous product testing revealed that moving the safety switch on the XPR rifle “may cause movement in the trigger system that could result in unintended firing of certain XPR rifles”. Accordingly, Winchester will replace certain trigger group parts in Winchester XPR rifles at no charge to the customer. Winchester requests that all owners of XPR rifles send their rifles back to the factory for retro-fitting.
For more details on how to return your rifle for retro-fitting, or if you are unsure if your rifle is included in the recall, or if you have any other questions, call 1-800-727-4312 or e-mail Winchester at XPR@winchesterguns.com. You can also CLICK HERE to view the Recall Notice and do a Serial Number search to verify your recall status. (By the terms of the notice, it appears that ALL XPRs are subject to the recall).
WARNING: Do not load or shoot any XPR rifle until it has been returned to the Winchester Service center and Received a retrofit. Failure to follow this warning may result in a risk of harm, including serious personal injury or death to you and others.
That smart phone in your pocket is really a miniature computer. What if you could harness that electronic brain to work as a weather meter? You’d just need a way to feed the smart phone environmental data — temperature, humidity, air pressure, wind velocity and so on. Well now that’s possible with the new $69.00 Weatherflow Smart Phone Weather Meter.
This portable, multi-function Weather Meter provides key weather data to your iOS and Android Mobile devices wirelessly via BlueTooth. The unit measures temperature, humidity, air pressure and dew points. With its built-in impeller, the Weather Meter will also record wind speed (average and gust), and wind direction. You can hand-hold it or attach it to a pole/tripod with a standard camera mount. This wireless Weather Meter is compatible with iPhone, iPad, iPod Touch and all major Android devices. The best thing is the price — right now the unit is just $69.00 at Amazon.com.
Reviews by Weather Meter Purchasers
By Wiley on October 2, 2015 — Verified Purchase
I own and love the original WeatherFlow Wind Meter but when I saw this new one that includes temperature, humidity and pressure for under $100, I had to have it. My new weather meter arrived two days after I ordered it and I am amazed at how good this thing is. Solid and well-built, it’s super comfortable in your hand. The hard carry case is nice. The App is pretty simple – start the App and push the button to connect. The meter connected without issue to my iPad mini and my Galaxy S5 (Android) phone. It displays the extra sensor information elegantly, and the data agrees very well with the Davis weather station on my neighbor’s house. Saving and sharing reports is simple. Something cool that’s not obvious until you play with the App a bit are the ‘more data’ you can see (wind chill, heat index, crosswind, headwind, and many others including some I didn’t know existed). I’ve used various Kestrel meters over years and while they are good sensors, Kestrel’s higher price and lack of smart phone integration (or any easy way to get data off the thing) have been frustrating. [Editor: Kestrel’s brand new 5000 Series Weather Meters do offer Bluetooth connectivity as an optional extra.]
By Richard W. on October 27, 2015 — Verified Purchaser
Great device for the price. It would be nice to interface it with ballistics Apps… but it provides relatively accurate readings and is very small. Finding wind direction is a bit manual (you have to face the device into the wind), but how hard is that? The Bluetooth connectivity is great, you don’t actually have to have it physically connected to the phone — you can put it where you need it.
Technical Details — Compatibility and Settings
The WeatherFlow Weather Meter processes data via a free downloadable App for iOS or Android. The unit works with Apple iPhones 4S or newer, Apple iPads Gen 3 or newer, iPod Touch, and “all major Android devices”. Wireless functionality requires support for Bluetooth version 4.0. You can select either English or Metric units via the “settings” menu. Wind speed units/range are 0.5 to 140 mph; 0.4 to 122 Knots; 0.8 to 225 kph; 0.2 to 63 m/s. Pressure units/range are: 8.9 to 32.5 inHg; 300 to 1100 mbar.
Product Tip from Boyd Allen. We welcome reader submissions.
A while back, Roy Bertalotto acquired a budget-priced Kimber 82G rimfire target rifle from the CMP. The Kimber comes with an oiled-wood stock that works fine for three-position training, but Roy wanted to shoot the gun for the bench. The original Kimber stock, with its narrow, radiused forearm, was not ideal for this purpose. Roy wanted a wide, flat fore-end, which is much more stable in the bags. Rather that spend hundreds on a new benchrest stock, Roy modified his Kimber’s original stock by slicing a section off the bottom of the stock and then replacing this with a 3/4″ X 2 3/4″ X 15″ piece of walnut.
WATCH Project Stages in Slide-Show Below:
Roy explains: “The modification I did on my Kimber 82G stock was done using a milling machine, hand planes, files, die grinder and sand paper. It can also be done with simple hand tools — it will just take longer. The first step is removing the wood on the bottom of the fore-end. This was accomplished in the milling machine. A scrap piece of 2X8 was mounted to the milling machine’s table and the surface milled to be perfectly flat. The Kimber stock was screwed to this 2X8 with two large screws and the bottom of the stock was milled flat. Once this was done, a piece of 3/4″ X 2 3/4″ X 15″ walnut was glued using West System epoxy to the cut out area. I use West System epoxy in boat building, but any good wood glue will work.”
After gluing the new bottom piece in place, Roy milled the sides to provide side flats with a radius to transition from the wider lower section to the narrower upper part of the fore-end. As a added enhancement, Roy contoured the rear of the fore-end to blend with the rear of the stock, adding what he calls “1965 Ford Mustang side scoops”. Roy then used a Die Grinder with a 1.5″ sanding wheel to modify the wrist area to provide more thumb relief.
Following the cutting, milling, gluing, and shaping, Roy sanded with 150 grit and 300 grit sandpaper before applying multiple coats of Tung Oil. Once the main stock was completed, Roy completed the project by crafting an extended buttplate from a couple pieces of 1/8″ aluminum and two 1.5″ aluminum tubes, “all polished to a slightly less than mirror finish”. NOTE: This metal buttplate assembly was made from scratch (other than the pad). This is not an aftermarket extension kit.
Overall the gun turned out very nicely. Log on to Roy’s RVB Precision webpage to learn more about this Kimber stock modification project, and view more photos of the building process.
Have you recently purchased a new scope? Then you should verify the actual click value of the turrets before you use the optic in competition (or on a long-range hunt). While a scope may have listed click values of 1/4-MOA, 1/8-MOA or 0.1 Mils, the reality may be slightly different. Many scopes have actual click values that are slightly higher or lower than the value claimed by the manufacturer. The small variance adds up when you click through a wide range of elevation.
In this video, Bryan Litz of Applied Ballistics shows how to verify your true click values using a “Tall Target Test”. The idea is to start at the bottom end of a vertical line, and then click up 30 MOA or so. Multiply the number of clicked MOA by 1.047 to get the claimed value in inches. For example, at 100 yards, 30 MOA is exactly 31.41 inches. Then measure the difference in your actual point of impact. If, for example, your point of impact is 33 inches, then you are getting more than the stated MOA with each click (assuming the target is positioned at exactly 100 yards).
How to Perform the Tall Target Test
The objective of the tall target test is to insure that your scope is giving you the proper amount of adjustment. For example, when you dial 30 MOA, are you really getting 30 MOA, or are you getting 28.5 or 31.2 MOA? The only way to be sure is to verify, don’t take it for granted! Knowing your scopes true click values insures that you can accurately apply a ballistic solution. In fact, many perceived inaccuracies of long range ballistics solutions are actually caused by the scopes not applying the intended adjustment. In order to verify your scope’s true movement and calculate a correction factor, follow the steps in the Tall Target Worksheet. This worksheet takes you thru the ‘calibration process’ including measuring true range to target and actual POI shift for a given scope adjustment. The goal is to calculate a correction factor that you can apply to a ballistic solution which accounts for the tracking error of your scope. For example, if you find your scope moves 7% more than it should, then you have to apply 7% less than the ballistic solution calls for to hit your target.
NOTE: When doing this test, don’t go for the maximum possible elevation. You don’t want to max out the elevation knob, running it to the top stop. Bryan Litz explains: “It’s good to avoid the extremes of adjustment when doing the tall target test.I don’t know how much different the clicks would be at the edges, but they’re not the same.”
Should You Perform a WIDE Target Test Too?
What about testing your windage clicks the same way, with a WIDE target test? Bryan Litz says that’s not really necessary: “The wide target test isn’t as important for a couple reasons. First, you typically don’t dial nearly as much wind as you do elevation. Second, your dialed windage is a guess to begin with; a moving average that’s different for every shot. Whereas you stand to gain a lot by nailing vertical down to the click, the same is not true of windage. If there’s a 5% error in your scope’s windage tracking, you’d never know it.”
Verifying Scope Level With Tall Target Test
Bryan says: “While setting up your Tall Target Test, you should also verify that your scope level is mounted and aligned properly. This is critical to insuring that you’ll have a long range horizontal zero when you dial on a bunch of elevation for long range shots. This is a requirement for all kinds of long range shooting. Without a properly-mounted scope level (verified on a Tall Target), you really can’t guarantee your horizontal zero at long range.”
NOTE: For ‘known-distance’ competition, this is the only mandatory part of the tall target test, since slight variations in elevation click-values are not that important once you’re centered “on target” at a known distance.
At the 2015 F-Class National Championships, nearly three-quarters of the F-Open shooters were using SEB coaxial front rests. And the man who makes them, Sebastian Lambang, was on the firing line too. Seb shot very well, finishing in second position in the F-TR division for the Saturday (Oct. 31) session. For those shooting F-Open or benchrest matches, Seb’s joystick rests really do represent the current state-of-the-art in front rest design. Courtesy of Seb, here are some photos that illustrate the “inner workings” of the SEB NEO Front Rest.
If you’ve ever wondered how a joystick front rest works, and how the parts go together, study the photos below. In addition, for those who use a NEO rest in competition, Benchrest Champion Mike Ratigan offers some PRO USER Tips that will help you get the best results from your NEO.
Unique Features of the SEB NEO Front Rest:
Lots of Travel — 43 MOA Vertical and 48 MOA Horizontal via joystick alone. The NEO offers more joystick travel than any other coaxial rest.
Variable Joystick Movement — The NEO is the only rest that can be configured for reverse action mode. That means you can optionally set it to lower the rifle with an up movement of the joystick if you prefer. (Standard setting raises rifle with up joystick movement.)
Rack & Pinion Risers — The NEO has dual support columns with Rack & Pinion system, offering a very broad vertical adjustment range.
Optional Counter-Weights — The NEO comes standard with a spring-loaded top mechanism to help hold up the rifle. Optional counter-weights allow you to reduce spring “pre-load”. Many people feel the counter-weights also allow a smoother, less jerky movement.
Reversible Base — The NEO’s base can be set-up with either the long leg in the rear or the long leg in the front. Putting the long leg in front gives more room under the rifle.
NEO Packs Flat — The SEB NEO is easily dismantled for transport, and can pack nearly flat. This is a big advantage when traveling.
Counter-weight Function and Calibration: “With the Seb NEO, equipped with the optional static counter-weight, the shooter can calibrate the counter weight to the rifle weight. The counter-weight is used to hold up the rifle. Clamping pressure of the sliding plates is NOT used to hold up the rifle like other coaxial rests on the market today. Other coaxial rests apply enough clamping force to the rest top mechanism sliding plates to resist the downward movement of the top when the rifle weight sets on the rest. This one feature of the Seb NEO almost completely eliminates bullets falling out of the bottom of your groups because the rest moved (or falls) down when you fired the rifle. This function is very important.”
On Hand Position: “I try to keep the palm of my hand grounded to the bench at all times. To do this at the closer distances, the handle will be laying flat (bend to the side) while shooting on the bottom of the target. To move to the top up (for right-handed shooters) I rotate the handle counter clockwise, which [raises the top] while maintaining my palm grounded to the bench.”
On Front Bag Fill: “Give some coarse sand blasting sand a try with the small stuff screened out. This will help reduce compaction from daily use.”
We’ve all heard the old adage: “Keep your powder dry.” Well, tests by Norma have demonstrated that even normal environmental differences in humidity can affect the way powders burn, at least over the long term. In the Norma Reloading Manual, Sven-Eric Johansson, head of ballistics at Nexplo/Bofors, presents a very important discussion of water vapor absorption by powder. Johansson demonstrates that the same powder will burn at different rates depending on water content.
Powders Leave the Factory with 0.5 to 1.0% Water Content
Johansson explains that, as manufactured, most powders contain 0.5 to 1% of water by weight. (The relative humidity is “equilibrated” at 40-50% during the manufacturing process to maintain this 0.5-1% moisture content). Importantly, Johansson notes that powder exposed to moist air for a long time will absorb water, causing it to burn at a slower rate. On the other hand, long-term storage in a very dry environment reduces powder moisture content, so the powder burns at a faster rate. In addition, Johansson found that single-base powders are MORE sensitive to relative humidity than are double-base powders (which contain nitroglycerine).
Tests Show Burn Rates Vary with Water Content
In his review of the Norma Manual, Fred Barker notes: “Johansson gives twelve (eye-opening) plots of the velocities and pressures obtained on firing several popular cartridges with dehydrated, normal and hydrated Norma powders (from #200 to MRP). He also gives results on loaded .30-06 and .38 Special cartridges stored for 663 to 683 days in relative humidities of 20% and 86%. So Johansson’s advice is to keep powders tightly capped in their factory containers, and to minimize their exposure to dry or humid air.”
Confirming Johansson’s findings that storage conditions can alter burn rates, Barker observes: “I have about 10 pounds of WWII 4831 powder that has been stored in dry (about 20% RH) Colorado air for more than 60 years. It now burns about like IMR 3031.”
What does this teach us? First, all powders start out with a small, but chemically important, amount of water content. Second, a powder’s water content can change over time, depending on where and how the powder is stored. Third, the water content of your powder DOES make a difference in how it burns, particularly for single-base powders. For example, over a period of time, a powder used (and then recapped) in the hot, dry Southwest will probably behave differently than the same powder used in the humid Southeast.
Reloaders are advised to keep these things in mind. If you want to maintain your powders’ “as manufactured” burn rate, it is wise to head Johannson’s recommendation to keep your powders tightly capped when you’re not actually dispensing charges and avoid exposing your powder to very dry or very humid conditions. The Norma Reloading Manual is available from Amazon.com.
Real-World Example — “Dry” H4831sc Runs Hotter
Robert Whitley agrees that the burn rate of the powder varies with the humidity it absorbs. Robert writes: “I had an 8-lb. jug of H4831SC I kept in my detached garage (it can be humid there). 43.5-44.0 gr of this was superbly accurate with the 115 Bergers out of my 6mm Super X. I got tired of bringing it in and out of the garage to my house for reloading so I brought and kept the jug in my reloading room (a dehumidified room in my house) and after a few weeks I loaded up 43.5 gr, went to a match and it shot awful. I could not figure out what was going on until I put that load back over the chronograph and figured out it was going a good bit faster than before and the load was out of the “sweet spot” (42.5 – 43.0 gr was the max I could load and keep it accurate when it was stored in less humid air). I put the jug back in the garage for a few weeks and I now am back to loading 43.5 – 44.0 gr and it shoots great again. I have seen this with other powders too.”
If you have two jugs of the same powder, one kept in a room in your house and one somewhere else where it is drier or more humid, don’t expect the two jugs of the same lot of powder to chrono the same with the same charge weights unless and until they are both stored long enough in the same place to equalize again.
Berger has released two important informational updates for its line-up of bullets. First, the Ballistics Coefficients (BCs) have been updated for the vast majority of bullets Berger sells. In addition, G7 model BCs are being provided for most of the bullets. You will want to use the updated BC data, which is based on actual testing of recent production lots of bullets.
Second, Berger is now providing a dual twist-rate recommendation for most bullets. Berger is now lists a “minimum” barrel twist rate as well as an “optimal” twist rate. To get maximum long-range performance from your bullets, use a barrel with the “optimal” rate of twist.
CLICK HERE for the latest Berger Quick Reference Sheets with updated BCs and new Optimal Twist Rates. Eric Stecker, Berger President says: “We have tested every lot of bullets produced in the last several years to bring you these updated numbers for all of our bullets.”
Ballistic Coeffificent (BC) Updates with G7 Data
Berger notes: “We have updated all of our Ballistic Coefficients to be even more accurate.
Prior to 2008, all of Berger Bullets’ BCs were calculated using a computer prediction. Early in 2009, we began measuring BCs with live-fire testing. As a result, Berger’s BCs were updated and G7 BCs were also made available. This represented a dramatic improvement in the accuracy of performance data at that time. Since 2009, the BCs assessed for Berger Bullets have not been updated. As part of our ongoing effort to provide shooters with the best information possible, Berger has been testing every lot of bullets produced for the last several years. The result is updated and highly accurate running averages of BCs for recent production lots.
Here are some of the Updated BC Values for popular Berger Target (Match) Bullets:
G7 Form Factor Addition
Berger also added the G7 form factor to the Ballistics Quick Reference Sheet. The analysis of form factors can be very useful when considering a bullet’s long range performance potential. Going by BC alone can be deceptive since BC includes the weight and caliber of the bullet. Form factor indicates how much drag the bullet has, which is a very important consideration for all bullets of all calibers.
NEW Dual Twist-Rate Recommendations
Recommended twist rates for bullets are commonly listed as a single value, such as 1:12” (one rotation in 12″ of barrel travel). This may be overly simplistic. There is a big gray area of marginal stability in which bullets can fly with good accuracy, but with a reduced (i.e. sub-optimal) Ballistic Coefficient. Recognizing this reality, Berger is now listing two twist rates for each bullet it makes. The first is the minimum twist needed for good accuracy, which Berger has always recommended. The second is the new optimal twist rate, which is the twist that will stabilize the bullet to a level which achieves its full performance (BC) potential. CLICK HERE For more information.
When you’re out at the range, the Earth seems very stable. But it is actually a big sphere zooming through space while spinning around its axis, one complete turn every 24 hours. The rotation of the earth can create problems for extreme long-range shooters. During extended bullet flight times, the rotation of the planet causes an apparent deflection of the bullet path over very long distances. This is the ballistics manifestation of the Coriolis Effect.
Verifying Scope Level With Tall Target Test
Tests Show Burn Rates Vary with Water Content
