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September 10th, 2008
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 July issue of Precision Shooting Magazine, Fred Barker reviews the current Norma and Vihtavuori reloading manuals. Fred notes that, in the Norma manual, Sven-Eric Johansson, head of ballistics at Nexplo/Bofors, presents a very important discussion of water vapor absorption by powder. Johansson shows, with supporting test data, that the same powder will burn at different rates depending on its 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
Reviewer 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 IMR3031.”
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 a variety of sources, including MidwayUSA.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. Been there … done that!” |
Do Your Own Test with Sun-Dried Propellants
Johansson studied the effects of humidity variances during long-term storage. Keep in mind that a powder’s water content can change in a much shorter period of time if it is exposed to extreme heat, or if it is used in a very humid environment. You can do your own simple test to show how heat can de-hydrate powder. Throw 100 grains of powder and weigh it. Then put it out in direct sunlight for a full day (shielded from the wind so you don’t lose any kernels). Re-weigh the sun-dried powder. You’ll find it has lost a bit of weight from the water baking out.
September 1st, 2008
As a cartridge case is reloaded multiple times, burnt powder residue and carbon builds up on the inside of the case. Unless the case interior is cleaned in some fashion, eventually you’ll see a reduction in case capacity. One of our Forum members from Australia wonders about the effects of reduced case capacity: “If the capacity of the case decreases as the crud builds up, then it effectively reduces the chamber size. Wouldn’t that change the pressure produced from that of an equivalent clean case?”
Ultrasonic Cleaning Example:
Interesting Test of Case Capacity Changes
Forum member Fred Bohl has actual test results that can help answer the above question. Fred proved that, over a 20-reload cycle, the case capacity of uncleaned cases did, indeed, decline a small amount. However, surprisingly, this did not seem to affect the actual chronographed velocity of the load. ES did increase, but Fred believes the higher ES was due to changes in case-neck tension, rather than due to the slight reduction in case capacity.
Fred reports: “Back when beginning to use ultrasonic case cleaning, part of the motivation was to get the inside clean based on the assumption that allowing burnt residue to build up inside cases would affect capacity, and, ultimately, performance. An experiment was done to test this hypothesis. The load used, 30.5 grains of RL15 behind 107gr SMKs in a 6mmBR, was selected for best group and lowest ES in prior load development. It turned out to be 92% of initial case capacity and neither “full” or compressed. (I would suspect that different powders, load weight, and total case capacity might produce very different results.)
We took 30 cases of identical initial capacity and tracked three lots of 10 each:
LOT 1: No Internal cleaning
LOT 2: Cleaned with media in tumbler
LOT 3: Cleaned with Ultrasound machine
Each case (in each lot) was shot and reloaded 20 times. The simplified results after 20 reloads of each lot were as follows:
Lot 1 (not cleaned) – 0.3 to 0.4 gr. loss of capacity, 5 to 8 fps greater ES.
Lot 2 (tumble cleaned) – 0.1 to 0.3 gr. loss of capacity, 4 to 6 fps greater ES.
Lot 1 (ultrasonic cleaned) – no loss of capacity, no detectable change in ES.
FINDINGS
There was no detectable correlation of velocity change to the lots. An oddity was that on very hot days Lot 1 velocities were, occasionally, slightly higher. [Editor’s note: That does suggest that the carbon build-up inside the uncleaned cases might cause a slight increase in pressure that shows up on hot days. Fred has posted that “A local shooter reported doing the 20 reload, no clean test on a .308 that gave a loss of capacity of 2.0 grains, doubled ES and signficant velocity changes. However, I don’t have any details on his load weight or powder.”]
NOTE: From results of another ongoing test, I believe the above differences in ES are probably due more to variance in bullet grip tension than case capacity. The ultrasound cleaned cases (LOT 3) did maintain the lowest ES, but we are not 100% sure of the reasons why. More consistent bullet seating might be the reason.
[Editor’s comment: Jason found that with his ultrasonically-cleaned cases, the inside of the necks got so “squeaky clean” that he needed to use dry lube in the necks. Jason uses the $10.95 dry lube kit from Neconos.com. This applies ultra-fine Moly powder to the neck using small carbon steel balls]
August 31st, 2008
Gunsmith Nat Lambeth (“RustyStud” on our Shooters’ Forum) offers the following advice for readers who need to ship rifles or major gun components (actions, barrels etc.) to gunsmiths or repair facilities.
“You have several options when shipping your guns to and from a Gunsmith. I’ve tried them all and had problems with them all. Here are some pointers:
1. Always package your unloaded firearm so that it is not loose and can’t work itself loose during transport. I recommend, at minimum, you use a hardcase inside a cardboard box. You can order a hard case from any of the 6mmBR.com website catalog advertisers. It will come in a nice cardboard box. Just open the end and slide it out. Put your gun in the plastic hard case (after oiling the metal parts) and slide it back into the box. Then tape and relabel the box. Make sure marking on the box does NOT identify the contents as a gun. (You may be required to identify the contents to the shipping company or U.S. Postal Service clerk however.) For a very expensive gun, consider using a wood shipping crate. I will be making some shipping cases from plywood and foam line them. I will have to charge my customer a deposit and when they return the shipping crate I will return their deposit.
2. Pack individual components carefully, and enclose them in separate bubble wrap (or styrofoam) if there is any chance the parts can contact one another. Your editor had an experience where the finish of a fine, blued handgun was ruined because the repair facility had placed old, replaced trigger parts loosely in a foam-lined case with the handgun. During shipping these spare parts worked back and forth, gouging and scratching the pistol.
 
3. Confirm the recipient’s address BEFORE you ship. Individuals and businesses change locations all the time. Don’t assume an address you used a few months ago is still valid. It’s tempting to use old addresses that are pre-configured in the UPS or Fedex web-based shipping programs, but you should always confirm address validity prior to shipping.
4. Always put the sender’s and recipient’s telephone number on the outside of the box with the address. I have neighbors call me all the time saying I have a box that was delivered to them by mistake. If there is any way the label could be torn off or ripped, write the number on the cardboard with a felt pen.
5. Always send your packages insured for full replacement value. Take time-dated pictures of the contents before you ship. (This is yet one more reason to get an inexpensive digital camera, such as the Canon A590IS.) If you’re shipping a firearm with special collectors’ value, deluxe wood, or engraving, be sure you have detailed, high-quality photos of the item so you can prove its worth.
6. Always send firearms and expensive components “Adult Signature Required” if by FedEx, UPS, or DHL. If they are sent via U.S. Postal Service, send them restricted delivery. This insures a tracking number and verification they got to their destination. If you ship USPS, it’s not a bad idea to pay a little extra for the green return receipt. That’s one more piece of evidence that works in your favor if the recipient claims non-delivery. The green card also reminds the carrier to confirm the address.
7. Keep all your shipping documentation for a year after the package has been received. There could be a unseen damage that turns up several months down the road. This illustrates the importance of carefully inspecting items you receive immediately. Don’t let a box sit around for days before you open it.
8. Handguns are by law required to be sent by common carrier (unless you are an FFL holder). Most of the common carriers have their own rules requiring overnight or next day delivery. Long guns can be sent by ground and you can use the U.S. Postal Service. Companies such as FEDEX and UPS may try to stick you with a higher cost shipping bill by claiming that rifles and shotguns must go next day or air. That is not true. Long guns can be shipped via ground. Do check local laws however–California has special rules regarding ARs and registered “assault weapons”.
 9. Keep an eye on your gun by monitoring the tracking number. You can do this online with FEDEX, UPS, and USPS. If your package does not reach its intended destination, when it is supposed to be there, then initiate a traceright away. Don’t wait.
When Something Goes Wrong–Filing Claims
In my experience it takes from 7 days to 10 months to get a settlement on a claim. Don’t hesitate to take a shipper to small claims court if necessary. If the shipper gives you the run-around, filing a small claims action may be the best $40.00 you can spend. It only costs $40.00 to start a small claims action and the subpoena is another $5 bucks. Usually sending a subpoena to an officer will result in a rapid settlement. It is cheaper for the carrier to settle than have their corporate bigwig stuck in some small claims action. Realize the carrier usually is not the insurer.
I have had two claims within the last 10 weeks and neither has been settled yet. In both cases the barelled action was double-boxed ,and in one case it was also inside a piece of schedule 80 PVC pipe and was broken. The other was in a double-walled cardboard box. The action was bent at the action barrel juncture, it now looks like a boomerang. The muzzle was pushed through six layers of double wall corrugated box.
I quit using UPS over a year ago. Depending on how FEDEX settles these last two claims, I’ll decide whether I use their services again. Your editor prefers FEDEX as he has found that they paid non-delivery claims swiftly and at full value. One thing for sure, if you use USPS you have the Postal Inspectors and the BATF looking for your gun if it is lost.”
August 25th, 2008
Some folks feel that they don’t have to worry about rust and corrosion on stainless steel barrels, actions, and other components. That’s not really true. “Stainless” is a bit of a misnomer. First, there are different types of stainless steel alloys, with different degrees of rust resistance. 300 series stainless is more corrosion resistant than the 416 stainless commonly used in barrels. The composition (by percentage weight) of 416 stainless is 0.15% carbon, 12-14% chromium and the rest iron. 416 stainless steel lacks the roughly 10% nickel content that makes the 300 series more corrosion resistant in atmospheric conditions.
Though some grades of stainless are more corrosion-resistent, ALL varieties of stainless steel can rust if they are not handled and stored properly. Forum reader Kells81 observed: “Wanna see some rusted stainless? Go to the big “C” brand store in Ft. Worth. Every stainless gun they have on the used gun rack is rusted.” Tom Easly of TRE Custom explains: “Sweat is very corrosive. Sweat and blood will rust many stainless steels. I hate to handle my guns or drip on them when I sweat. It really helps to just wipe them good with a wet rag, dry and wipe on a light coating of gun oil. I think most stainless barrels are made from type 416 stainless, and it is generally pretty corrosion resistant, but not when exposed to sweat, blood, or chlorates (corrosive priming), and some other electrolytes.”
Forum member Jacob, who is studying materials science at LSU, provides this technical information: “The basic resistance of stainless steel occurs because of its ability to form a protective coating on the metal surface. This coating is a ‘passive’ film which resists further ‘oxidation’ or rusting. The formation of this film is instantaneous in an oxidizing atmosphere such as air, water, or other fluids that contain oxygen. Once the layer has formed, we say that the metal has become ‘passivated’ and the oxidation or ‘rusting’ rate will slow down to less than 0.002″ per year (0.05 mm per year).
Unlike aluminum or silver, this passive film is invisible in stainless steel. It’s created when oxygen combines with the chrome in the stainless to form chrome oxide which is more commonly called ‘ceramic’. This protective oxide or ceramic coating is common to most corrosion resistant materials.
Halogen salts, especially chlorides, easily penetrate this passive film and will allow corrosive attack to occur. The halogens are easy to recognize because they end in the letters ‘ine’. Listed in order of their activity they are: fluorine, chlorine, bromine, iodine, astatine.
These are the same chemicals that will penetrate Teflon and cause trouble with Teflon coated or encapsulated o-rings and/ or similar coated materials. Chlorides are one of the most common elements in nature and if that isn’t bad enough, they’re also soluble, active ions. These provide the basis for electrolytes. The presence of electrolytic solutions can accelerate corrosion or chemical attack.”
 CONCLUSION: Stainless steel barrels and components won’t rust nearly as fast as blued steel, but you still have to take precautions — particularly removing sweat and corrosive salts from the barrel. Also, don’t let moisture build up inside or outside of the barrel.
We recommend wiping your barrels and actions with Eezox, or Corrosion-X after each use. These are both extremely effective rust-fighters that go on thin, without leaving a greasy residue. (Eezox leaves a clear finish, while Corrosion-X has a slightly waxy finish.) Also store your guns in Bore-Store synthetic bags when the guns go in the safe. Bore-Stores wick away moisture, and the synthetic fleece inner surface is treated with rust-fighting chemicals. Bore-Stores also protect your guns against dings and scratches. To discuss rust formation on stainless steel, visit this FORUM Thread.
August 24th, 2008
This may surprise you. We’ve learned that time (between neck-sizing operation and bullet seating) can have dramatic effects on neck tension. Controlling neck tension on your cases is a very, very important element of precision reloading. When neck tension is very uniform across all your brass, you’ll see dramatic improvements in ES and SD, and your groups will shrink. Typically you’ll also see fewer fliers. Right now, most reloaders attempt to control neck tension by using different sized neck bushings. This does, indeed, affect how firmly the neck grips your bullets. But time of loading is another key variable.
 James Phillips discovered that time is a critical factor in neck tension. James loaded two sets of 22 Dasher brass. Each had been sized with the SAME bushing, however the first group was sized two weeks before loading, whereas the second group was neck-sized just the day before. James noticed immediately that the bullet seating effort was not the same for both sets of cases — not even close.
Using a K&M Arbor press equipped with the optional Bullet-Seating Force Gauge, James determined that over twice as much force was required to seat the bullets which had been neck-sized two weeks before. The dial read-out of seating force for the “older” cases was in the 60s, while the seating force for the recently-neck-sized cases was in the 20s. (These numbers correspond to pounds of force applied to the bullet). Conclusion? In the two weeks that had elapsed since neck-sizing, the necks continued to get tighter and stiffen.
Lesson learned: For match rounds, size ALL your cases at the same time. If you want to reduce neck tension, load immediately after sizing.
August 19th, 2008
Denver Instrument, maker of the MXX and Timberline Series of precision balances, has created a helpful guide explaining how to get the best performance from a digital scale. Denver Instrument knows that, to achieve and maintain a very high level of accuracy with digital scales, they must be calibrated regularly, leveled properly, and kept away from sources of interference. Unfortunately, some reloaders treat their electronic scales as if the machines were toasters — something to place on a tabletop, plug into an outlet, then “set and forget.” There’s a better way to set up your scale and keep it functioning optimally. Here are ten guidelines provided by Denver Instrument. Follow these “TEN Commandments” and you’ll benefit:
 10 COMMANDMENTS OF GOOD BALANCE USE
ONE: Thou shalt choose the best resting spot. The performance of your balance depends greatly on the surrounding environment. Choose a location away from the main traffic flow of the room, especially doors. Also be aware of heating and cooling vents as these produce air movement. You can adjust the environmental settings on your balance to provide the best performance in the chosen location. Balances must be placed away from magnets as they affect the weigh cell performance.
TWO: Thou shalt avoid vibrations. Vibrations can come from large machinery in production environments and from fume hoods in laboratories. An alternative to fume hoods are Power Safety Workstations which are designed specifically for use with a balance.
THREE: Thou shalt watch temperature changes. On an analytical balance a one degree temperature change can cause a 1 digit (0.0001g) drift. Although Denver balances have temperature correction built-in, it is still important to calibrate your balance when the temperature changes significantly. Choosing to place your balance in a temperature controlled room, away from sunlight, and calibrating often helps minimize the effects of temperature.
FOUR: Thou shalt calibrate often. Upon installation and each time the balance is moved you should calibrate your balance. For example moving an analytical balance to a location that is only 13 feet higher changes the weight reading from 200.0000 g to 199.9997 g; which means the result is 0.0003 g lighter than the actual mass.
FIVE: Remember to check the level. The instrument should be leveled upon installation with all feet (two front feet for round pan units, four feet for square pan units) touching the countertop. If the level changes, the balance should be re-leveled and recalibrated. As an example, a 200g sample would weigh 0.0025 g less when tilted at an angle of 0.3°.
SIX: Honor thy weights. Keep in mind that weights are only as reliable as their quality and certification. Remember, a 1 g does not weigh precisely 1.00000 grams. Weights should be recertified annually. Denver Instrument offers recertification services on all weights 1 mg to 5 kg. Check to make sure you have selected the proper weight class for your balance. The weight tolerance should be better than balance readability. Always use tweezers or gloves when handling weights as smudges and indentations change the value of the weight. Keep weights in cases so they don’t get scratched or dusty.
SEVEN: Thou shalt always use a small container and weigh in the center of the pan. Especially when using an analytical balance, the effects of air buoyancy increase as the sample container size increases. Using a small sample container will minimize the effects. Items placed on the pan provide a downward force. Placing them directly in the center of the pan keeps corner loading errors at a minimum.
EIGHT: Thou shalt not unplug. To perform within published specifications balances must have power applied for 30 minutes to 48 hours depending on the resolution of the balance. Denver balances have a standby mode which turn the display to standby but keep power cycling through the electronics.
NINE: Thou shalt not ignore static. Static is one of the most common weighing “noises”. It can cause reading to appear too high, too low or just be unstable. Denver balances include grounding methods to reduce the effects of static. However sometimes extra supplies are needed. Consider anti-static weigh dishes, anti-static brushes or low tech ways to increase the humidity of the chamber like placing damp cotton balls or glass wool in a small vial in the corner of the analytical draft shield.
TEN: Thou shalt clean often. Dirty weigh pans and powder in weighing chamber can contribute to static issues and lead to a wide variety of problems. Denver weigh pans are made from stainless steel and can be cleaned using a variety of household and laboratory chemicals. A small paint brush can be used to get power away from the edges of the draft shield for easy clean up.
August 15th, 2008
Grant, one of our Forum members from New Zealand, asked if there was a universal shell-holder that could hold cartridges securely for neck-turning, trimming, and case prep. He complained that the screwdriver-type case holder he was using didn’t center easily, was hard to tighten, and the case sometimes came loose during rotation. Another forum member agreed that he has experienced the same problems using a screwdriver-type case-holder.
This editor has found that a K&M screwdriver-type case holder CAN work securely if you tighten the locking mechanism tightly with the supplied wrench. But then you need the wrench again to get the case OUT. We were interested to see if there was a better solution that held the case securely, yet was easy to lock and unlock without tools.
Forum member Gunamonth provided a solution: “I use a Lee Zip Trim three-jaw case holder. With a little practice it centers the case quite nicely and holds just about anything. Chuck it in a cordless drill and have at it. It is much better than either the K&M or Sinclair [case-holder] in my opinion and the Zip Trim jaw is a lot cheaper (about $12.00). To use with power, you also need the Zip Trim three-jaw spindle, which is another $2.00.”
August 1st, 2008
With the relentless pursuit of more velocity and the “next higher node” by many reloaders, it is important to pause and think about safety. And one has to remember that most brass will not hold up to high pressure the way Lapua or RWS does. Many readers have asked us: “How does one detect excess pressure?”. Well first, one can obviously monitor the primer pockets and measure the diameter of the case near the web. Excessive stretch or pocket loosening is a sure sign you’re running too hot. There are also many visible signs of over-pressure which you can see. Reader ScottyS provided this comparison photo of cases, showing the tell-tale signs of over-pressure.
Scotty tells us: “These samples were from a lot of Federal soft-point hunting ammunition that were fired in a custom .308 with a chamber on the tight side (although still allowing a .308 Winchester GO gauge). Among the pressure symptoms were heavy recoil, sticky bolt lift, and the left case had to be manually removed from the boltface. This demonstrates why: 1) you should never assume that all lots of factory ammo are the same (and safe); and 2) you should ALWAYS wear eye protection. This also shows how high pressure can spike once you approach maximum load levels.”
Scotty noted that there was a big pressure difference between the left case and the right case, although both were fired sequentially, and both were from the same lot of ammo. So take heed–always take precautions when testing new ammo, even if it is factory-loaded.
June 29th, 2008
 In Sierra Bullets’ X-Ring Quarterly Newsletter, you’ll find lots of useful info on ballistics and reloading. Among our favorite regular X-Ring features are the “Short Shots” offered by Sierra Technician Carrol Pilant. Here are some of Carrol’s tips.
General Reloading Advice
● When using a collet style case trimmer, try to tighten the collet down equally each time to keep lengths uniform. If you tighten it down hard, the case will be longer than one you tighten down lightly.
● A little lube on the pilot and cutter on a case trimmer every few cases will help keep it from trying to gall in the case mouth and helps keep the blades sharp and cutting smoothly. It makes trimming an easier task.
● When charging cases from a powder measure, use smooth uniform movement being sure to give powder time to fall into the powder drum chamber. Also be sure to give it time to fall into the case.
● When using mixed cases or cases that have been fired a different number of times, don’t be surprised to get erratic velocities and performance.
● Just because two bullets weigh the same doesn’t mean they can be loaded the same. The amount of bearing surface can vary drastically.
Photo by M. Dunlap
Handgun Reloading Tips
● In revolver cases, rather than try to seat and crimp in one stage, seat in one stage and crimp separately. You won’t have the bulge at the base of the crimp you often get when trying to do it in one stage.
● When roll crimping, if your cases are erratic lengths, your crimps will be erratic also. Cases should be trimmed to the same length.
June 28th, 2008
Three-gun match competitor Zak Smith employs a simple, handy means to store his elevation and wind dift data — a laminated data card. To make one, first generate a come-up table, using one of the free online ballistics programs such as JBM Ballistics. You can also put the information in an Excel spreadsheet or MS Word table and print it out. You want to keep it pretty small.
Below is a sample of a data card. For each distance, the card includes drop in inches, drop in MOA, drop in mils. It also shows drift for a 10-mph cross wind, expressed three ways–inches, MOA, and mils. Zak explained that “to save space… I printed data every 50 yards. For an actual data-card, I recommend printing data every 20 or 25 yards.” But Zak also advised that you’ll want to customize the card format to keep things simple: “The sample card has multiple sets of data to be more universal. But if you make your own data card, you can reduce the chance of a mistake by keeping it simple. Because I use scopes with MILS, my own card (bottom photo) just has three items: range, wind, drop in MILS only.”
Once you have the card you can fold it in half and then have it laminated at a local office store or Kinko’s. You can keep this in your pocket, tape it to your stock, or tie the laminated card to your rifle. If you regularly shoot at both low and high elevations, you may want to create multiple cards (since your ballistics change with altitude). To learn more about ballistic tables and data cards, check out the excellent “Practical Long-Range Rifle Shooting–Part 1″ article on Zak’s website. This article offers many other insights as well–including valuable tips on caliber and rifle selection.
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