2 August 2004
by Robert D. Beeman
Preliminary partial draft
Airgun projectiles have included lead pellets, lead and steel balls, lead coated steel balls, birdshot, bullets, capsules of shot, slugs, darts, sabots, arrows, spears, syringes, explosive torpedoes, paint or dye balls, C02 cylinders, beanbags, flash or noise devices, celebration streamers, various plastic objects, and, in some extreme examples, even such things as soda cans, dead pigeons, and potatoes. We'll cover some of these later, rather briefly, but the lead pellet claims primary attention as the main projectile of adult airgunners all over the world.
A few pellets are of the cylindrical style. These have a straight sidewall and probably evolved from earlier, straight wall "cat slugs" which had a spur, rib, or felt disc to provide a snug fit into the bore. Apparently, the only straight wall pellets now in regular production are the Sheridan® 5 mm (".20" caliber") pellet and the H&N 5.05 mm pellet for Sheridan® airguns. These pellets have a basal ring to engage rifling. Fit is quite critical; because of this, and performance problems, they should not be used in the several other 5 mm airguns which have more recently been developed. The Sheridan pellet is quite hard and therefore expands very little upon impact. Penetration is thus greater than would be expected for its velocity. This pellet will usually pass right through most small game without making a clean kill. The H&N cylindrical 5.05 mm pellet is somewhat softer and slightly more pointed, but its field performance can also be somewhat disappointing. The 5 mm airgun caliber was given a new lease on life when the Beeman® company first introduced a variety of truly high precision 5 mm airgun pellets in several different styles in the late 1970s. (A former owner of the Sheridan® company confided to me that when they really wanted to test the accuracy potential of the Sheridan airguns, that they used the precision Beeman 5 mm pellets!).
The most accurate airgun projectile is the modern, precision lead pellet with a waist that is constricted - giving the pellet an hour glass shape. Such waisted pellets are referred to as diabolo pellets in reference to the ancient game of Diabolo which used a wooden spool, with an hour-glass shape, which was juggled on a string between two hand-held sticks. The purpose of the constricted waist is to reduce friction and to provide a thin skirt which can expand to form an airseal and easily engage the rifling, even in bores of considerable manufacturing variation. Again we have a major contrast with firearms. The effect of most bore friction on firearm projectiles is swamped by the driving power of the powder's explosion and a relatively large bearing area is generally needed to provide, and maintain, good rifling engagement in firearms. However, modern airguns, with their limited power, derive considerable advantage using the diabolo design with its very limited areas of friction and expanding skirt. The aerodynamics of diabolo pellets are quite different than those of firearm bullets with long straight or curved lateral profiles. Also, it is clear the ballistics of super-sonic projectiles (most firearms) and sub-sonic projectiles (most airguns) are also quite different. Some of the implications of these points will be briefly considered later in this chapter.
Diabolo pellets usually are classified by their head shape since the head generally has the most profound effect on their performance. The shape of the middle area or waist of diabolo pellets also can have a great effect on their ballistic efficiency. In general, it seems better to have the waist near the center of the pellet than near the head. A waist near the head results in a very sharp undercut behind the head which may produce greater turbulence, and thus drag, than the gentle slope of the surface behind the head on other pellets.
There are four basic pellet head shapes in common use now: wadcutter, pointed, roundnose, and hollow point.
1. Wadcutter: These pellets have a flat head with a sharp edge. They primarily are designed to cut a maximum size, easily scored hole in paper targets. Because of the significance of this design to match shooters, from local competition to the Olympics, more effort has been put on the perfection of this design than any other pellet shape. Production of extremely precise pellets is a far more difficult business than is generally appreciated. Generally only the very special match grade wadcutter pellets from two German firms, Haendler und Natermann® and RWS®, and Crosman Airguns®, of the United States, are considered for serious competition all over the world. Their attention to manufacturing detail and design has lead to pellets which, in their finest grades, may well have the smallest minute of angle accuracy of any gun projectiles. Variables, such as diameter and weight variation, have been carefully controlled, but even more important are features which are not easily measured. These include concentricity of the head and skirt, gyroscopic stability due to even distribution of weight, minimal axial deformation, and consistency of head edge and skirt thickness. The size and uniformity of the head and skirt diameter has a large effect on the performance of unsized pellets. However, the pellet designers face a bit of a paradox in the design and size of the pellet head. It is generally felt that the optimum muzzle velocity for match pellets fired on 10 meter indoor ranges is in the 550-650 fps ( mps) range. It is desirable to have a pellet which produces the maximum size hole in the target paper because the highest scoring target ring which is touched by the hole is the score which is recorded for the competitor. One thousandth of an inch or a tiny fraction of a millimeter could win or lose the Olympics! Within the range of optimum velocity, it is desirable to reduce the shot time of the pellet so that it has a minimal period where it is subject to the movement of the shooter. Maximizing the size of the pellet head will, of course, maximize the hole cut by a given design of head edge. However, the more the head diameter is increased, the more the friction is increased. This means a decrease in velocity and an increase in shot time (and steeper trajectory - however, this is of no importance in indoor matches of fixed distance). Within reason, it is generally best to maximize the size of the head in order to obtain the highest scores in air rifle shooting. In the case of air pistol shooting, where the gun movement by the shooter is much greater than in rifle shooting, reduction of shot time and attainment of velocities near the optimum level are more important than the extremely subtle factor of hole size within a given caliber. Therefore, so-called "high speed" pellets have been developed for pistol shooters. The higher muzzle velocity of these pellets have been obtained by means of a slightly lower pellet weight and/or smaller head size. It must be emphasized that the higher velocity of these high speed pellets may largely be due to dimensional differences in specification; some of the high speed pellets may even be heavier than some regular speed pellets.
Wadcutter pellets are frequently selected for field use because of their excellent impact and limited penetration. For field use, the high speed versions generally are preferred, for the reasons discussed above. The flat head and soft lead of these pellets provide good initial impact force if they hit at high airgun velocities.
The sides of some pellets (including wadcutters) are smooth ("glatt"); others are ribbed ("geriffelt"). These are only cosmetic features and the difference probably is of no concern to shooters. It has been claimed that the smooth surface versions are slightly more uniform from the first to last lots from a given set of dies, but there apparently is no experimental evidence of this.
The intense concern with perfection in design and manufacture of match pellets formerly had been applied only to wadcutter pellets in .177" (4.5 mm) caliber, because that was the only airgun caliber used in international competition. Now some of the leading pellet makers are producing pellets of true match level quality in other calibers and styles. Of course, this has great significance to the field shooter who wishes to extract maximum performance from his field gun and to maximize his chance of success when firing at the extremely small lethal area of small game, etc.
2. Pointed: These pellets are designed for maximum penetration. The Silver Jet® pellet, introduced in the early 1970's, became extremely popular in those countries where airguns are used in the field. A rash of other pointed pellets soon appeared on the market. The Silver Jet is unique in several aspects. Instead of a single edge around the head, the head has three rings, the middle one has a slightly larger diameter to engage the rifling, a function that generally is reserved more for the skirt. While this may make this pellet slightly harder to seat, this is more than overcome by the lesser friction of the skirt and the effect of the multiple head rings in providing maximum resistance for any air that might "try to sneak by". Lack of blowby increases the efficiency of this pellet and also reduces harmful piston impact. The smaller, front and back head rings provide greater in-bore stability by riding on the rifling lands, a design feature which is intended to produce less in-flight wobble or "yaw".
3. Roundnose: The roundnose pellet design, sometimes known as "English style", was originally designed as an all-around pellet. The design does have distinct aerodynamic advantages and this generally produces less ballistic drag and thus good retention of velocity and a flatter trajectory curve. However, penetration and impact are compromised in comparison to other pellet designs. Some versions, such as the Beeman Laser®, combine the aerodynamic advantage of the round head with very light weight to give exceptionally high velocity. The demand for an extra heavy field pellet and the growth of metallic silhouette shooting with airguns prompted the development of a special variation of the roundnose pellet. This pellet is the Beeman Ram Jet® which has a weight of about 9.6 grams (624 mg) with a sharp, semi-wadcutter edge behind the round nose to catch the silhouette and thus score a knock down even on a glancing hit. The extra 35% of weight over the 7.13 grains of the Laser roundnose provides extra inertia to minimize the effect of side wind and to maximize impact and knock down power. While a sharp point pellet is the most effective in cutting through tissue, the round nose pattern is the most effective in passing through air at sub-sonic speeds. The shape of a falling drop of water demonstrates this aerodynamic principle quite well. As soon as the air has forced the falling droplet into the shape of least resistance, we see a rounded, blunt end going forward.
4. Hollow Point: Early in the 1970s, the Beeman Company invented a new style to add to the original basic three pellet styles. This first true hollow point pellet was introduced in a semi-wadcutter version as the Beeman Silver Bear®. This design was produced by H&N®, under paid license from Beeman®, as the H&N Semi-Wadcutter Hollow Point pellet. This pellet was designed to give excellent impact, even when hitting at velocities that are not sufficient to produce expansion. The very low weight allows extremely high velocity. Perhaps because the hollow point head builds a pressure cone of air while in flight, this head shape seems to have most of the ballistic advantages of the roundnose type. The semi-wadcutter edge produces a relatively sharp hole in paper targets and works well on silhouette targets if driven from a gun powerful enough to provide sufficient residual velocity at the most distant silhouette.
The Beeman Crow Magnum® pellet finally followed the great success of the Silver Bear hollow point pellet. Here there was a deliberate attempt to produce greater impact value by a huge “mouth” and more weight. Frankly, I really don’t think that any of the later attempts at making a big-mouth hollow point pellet have balanced performance nearly as well as this pellet. If you really want a maximum mouth, and are firing at close targets, try shooting just about any pellet backwards!
Importance of Quality:
Finally, consider that just as you need different types of firearm ammo for various purposes, there is no airgun pellet suited to all uses. You need several types and you need to determine which ones of each style perform best in your particular guns.
New shooters sometimes feel they don't need high quality pellets. Actually , both novice and expert need "all the help they can get". Errors of the shooter, the gun and the ammunition are cumulative. Fine pellets will dramatically reduce the group size of any shooter .To demonstrate this quickly, just guess what size groups you think you could shoot at 30 meters (33’) with perfect ammunition. Now draw a circle of about that diameter (perhaps 1"/25 mm, 1/2”/13 mm, or 1/4", 6.5 mm) on a piece of paper. Put a few dots on the line of your circle. These dots represent outer hits of your hypothetical group. Now, knowing that test results have shown that many pellets at best are capable of only 1/2”, 13 mm groups, draw a 1/2",13 mm diameter circle around each dot. Top quality pellets are capable of groups less then .04" diameter. So, repeat the procedure above but draw extremely tiny circles (about 4/100", 2 mm diameter) around each dot. Now compare the overall size of each diagram . Your first diagram represents how much your hypothetical group could have been expanded by the standard ammunition; your second diagram shows how little the group would be expanded by high quality pellets. For even the amateur difference could be 100%! Finally draw a circle which represents the potential center-to-center group size of a top expert with the best combination of air rifles and pellets. Utility pellets could enlarge his group several hundred percent. Field shooters should note that the difference between utility and top grade pellets gets even larger as the firing distance increases and can easily mean the difference between a hit and a wide miss.
Following the same logic as above, it can be seen that better, high quality pellets will shrink the potential size of groups fired from any airgun. An economy level airgun with high quality pellets could out-shoot a much higher priced airgun using utility grade pellets. Proper selection of better pellets can also increase velocity (up to 60-80 fps), and power, by providing better fit. Better fit, and lack of undersized irregulars, also means less air blow-by; this improves air cushioning of the piston and results in less jarring of the shooter, the gun's parts, and the sights. Poor pellets can ruin a good airgun.
MANUFACTURE OF PELLETS
Modern, commercial airgun pellets are produced by cutting special lead wire and then swaging the resulting pieces into the desired shape on automatic machinery. The surface of the waist area, including an embossed design , is rolled on from the side after the swaging process. The marks of the swaging dies generally can be detected under magnification. Exceptions are the Beeman Silver Jet pointed and Jet round nose pellets. These pellets are subjected to an extra, quite secret step which results in each pellet being effectively "lathe-turned". This effectively eliminates the swage marks and extra tip pieces that may be found on swaged imitations o f these pellets. This "lathe-turning” step adds a great deal to the expense of pellet production. This method is not known to most pellet makers, therefore very few pellets are produced by this method
At first pellets were produced from machines which could not closely control the weight or measurements of the resulting pellets. These machines are now known as first-generation pellet machines. Additional information on second and third generation pellets machines will be presented here later.
Quality is absolutely the most important variable in pellets and it varies enormously. One need only shake out a few pellets from several boxes of utility grade pellets and compare them, very closely or with a hand lens, with some top-grade sporting and match pellets. Utility pellets may have several hundred percent greater variation than top-quality pellets which may cost little more. Greater variation means poorer accuracy, larger groups and more misses
The cost difference per shot between crude and the finest pellets is indeed tiny. Remember, too, that low-quality pellets can actually injure your airguns. Irregular pellets allow excessive air blow-by and, for spring piston guns, this means less air cushioning for the piston. The resulting jarring reduces the life of the piston, mainspring, and other parts, loosens sights and causes shooter fatigue. Poor pellets simply are not worth the false economy. Life is too short to drink poor wine.
Pellets are generally packed in tinned steel or plastic containers. A few brands are bulk packed in boxes which have an expanded foam liner. This gives excellent protection during transportation. The impact of pellets against each other and the side of their container has significant effects on their accuracy, power, and wear and tear on the gun. Smoothing out the skirt of seated pellets with the special rounded end of a Pell-seat can eliminate all, or most damage to the pellet skirt which had resulted from manufacturing, transportation, and handling.
The very finest of match pellets are packed individually in compartments or foam sheets after they have been carefully mechanically and visually inspected. Generally such packing more than doubles the price of the pellets, but it is the only way to insure factory perfect pellets on the shooting line. Occasionally there will be batches of pellets which do not work as well in one gun as another and this has led to the rise of the myth t hat some bulk pack pellets shoot more accurately than the individually packed ones. Actually, many shooters, like many fishermen, secretly love myths and will cling to such stories long after the reason for them has disappeared. There was a time when individually packed pellets would oxidize more rapidly than bulk packed pellets, which often were better sealed, and this supported this story. However, since then the composition of the pellets was changed slightly to resist this problem, and packed pellet boxes are now sealed with air tight tape. Now it is extremely unlikely that bulk packed pellets could consistently perform as well as identical individually packed pellets.
Pellets are generally packaged in units from 100-1250 per package. Packages for 100 to 500 pellets traditionally were made of plated steel and known as “tins”. Many new airgunners look at a tin of 500 pellets and think how long it generally takes to use up 500 rounds of firearm fodder. Well, airgun shooting is different. It's easy to use up a whole tin in a weekend or less! It is amazing how often a new airgunner thinks a tin of 500 pellets is going to last forever but shortly is looking for a special price on a five pack or a carton of ten tins.
Composition of Pellets:
Almost all airgun pellets mainly are made of soft lead. No other material seems to offer such an excellent combination of weight and density, workability, rifling engagement, airseal, inertia, expansion upon impact, and resistance to ricochet. Small amounts of antimony and/or tin are sometimes alloyed into pellet lead to increase its hardness. Harder pellets resist handling and loading damage better, but they also may resist proper engagement by the rifling, and reduce velocity through increased friction and air blow-by. Penetration is increased, but expansion is reduced. A hard pellet may appear more effective in tests because of its greater penetration, but in use on game it probably would be less effective than an expanding pellet. A typical analysis on pellet lead is of the British Standard No. 602: 1956 II: Lead - not less than 99.25% and not more than 99.80%; Antimony - not more than 0.10%; Zinc - not more than 0.005%; Copper - not more than 0.07%; Tin - not more than 0.50%; and other elements - not more than 0.075%. Beeman/H&N pellets are 99.9% and .05% antimony. The addition of antimony has three purposes:
1. To improve the swaging process.
2. To protect the pellets against transportation damages.
3. To improve resistance to corrosion.
Airgun pellet lead apparently never contains significant amounts of arsenic. Arsenic is used in the production of some lead shot; its absence in airgun pellets may be of significance in legal and medical matters concerning pellets lodged in the body of humans or other organisms.
Metallic lead evidently is quite a safe, as well as an effective, material to use in airgun ammunition. Lead projectiles have only a small fraction of the ricochet hazard of steel, zinc, or other hard projectiles. It does not seem feasible that lead airgun projectiles could present a problem in the environment in the manner in which lead shotgun shot has been claimed to be an environmental problem. Shotgun shot is rained down in some truly enormous numbers in some waterfowl areas. This shot is then exposed to anaerobic degradation into possibly harmful secondary products, and this altered shot is distributed in such a manner that it can be ingested by feeding waterfowl. It is the resulting lead compounds that are a problem. The likelihood of a similar situation for airgun pellets seems almost inconceivable. And, it is very significant that lead projectiles permanently embedded in the body of humans, or other organisms, do not seem to involve a significant chemical hazard. Lead bullets and pellets have been carried embedded in various parts of humans for decades without apparent toxic effects. Thus it would seem that "lead free" airgun projectiles are an answer to a problem that doesn't exist.
One unusual, patented type of airgun pellet, and certain airgun darts, consist of a plastic sheath around a hard metal core. There have been great problems in producing and attaching plastic sheaths to these metal cores in a manner which maintains high accuracy - which is the absolute top factor in field use of airguns. The hard metal cores present ricochet problems, excessive penetration problems, and the composition of the cores and sheaths may present some interesting legal and medical aspects. That is, the core may be subject to corrosive damage when embedded in human or other, tissue, and the sheath, which can be separated from the core after penetrating the organism, may not be detectable by X-ray.
Other Airgun Projectiles
Shot are spherical projectiles usually made of steel or lead. Steel airgun shot are often referred to as "BB’s" (for “ball bearing”, their original source - but referring to them today as ball bearings is quite incorrect). The steel BB almost surely is the most common airgun projectile in the world - literally billions and billions are fired each year! Technically speaking, BB is now an official U.S. caliber, often referred to as .177”, or 4.5 mm, but actually having, by governmental standard, a maximum diameter of .175" and a minimum diameter of .162". The mean average of steel BBs generally is about .173" with a mean average weight generally about 5.3 grains. Regular steel BB's typically had two steel "flats" which result from the process of swaging them from steel wire. Precision BB's are ground down to a smooth, completely spherical surface for greater accuracy. Steel BB's are generally coated with copper or nickel to prevent rusting. Steel shot should not be used in any rifled bores except those designed specifically for them such as the dodecagonal rifling of the Daisy Powerline® series.
Lead airgun shot commonly are available in BB (.175" or 4.4 mm), .177” (4.5 mm), .20” (5.0 mm), .22" (5.5 mm), and .25” (6.35 mm) as well as many special sizes, both larger and smaller. Lead airgun shot are now specified to have a diameter of approximately .177” with a maximum shot start force of 22.5 lbs. or kg.). Precision lead balls are a precision form of lead shot, but lead balls fit an airgun's bore much better, wasting less air force and giving greater accuracy than similar size, regular lead shot or steel BB’s. The lead balls also reduce the ricochet and rebound danger, as compared to steel BB's, and give much more impact. Their trajectory, of course, is greater. Precision lead balls work well in the feed mechanism of many U.S. air and C02 repeating guns. However, retaining a lead BB may be a problem in some airgun models which depend on a magnet to hold the projectile to the bolt tip and the lead BB may be subject to greater mechanical damage by forceful feeding mechanisms. Imported lead shot is sometimes copper or nickel-plated and can be confused with steel shot. A test with a magnet or hammer can quickly clear up any doubt. Such coated shot are cleaner to handle and may feed better in repeater mechanisms.
Airgun darts were at one time quite popular. In the 18th and l9th century, shooting darts from elaborate, very expensive air rifles was an indoor sport for the rich. The darts involved were elaborate items in themselves, generally being made of a long steel body with a very sharp point and a tail of special hairs. A hair of special color was used as a marker to indicate the side of the dart which was to be placed upward when loading the gun. Individual hairs were trimmed or pulled until the flight of the reusable dart was so balanced that it hit perfectly each shot. Some of these ancient darts were as large as 1/2” (13 mm) in diameter. It seems that even fewer of the darts have survived than the antique airguns which fired them. Much smaller commercial steel darts with fiber filament tails were also popular earlier in the 20th century for use with fairly low power smoothbore airguns. They were fired into dart boards and used over and over again. Different color tails would allow identification of the darts fired by different shooters. Today darts are made in both .177" and .22" caliber (.25" darts are extremely rare). They will not feed into many of the smoothbore airguns and can damage the bores of rifled guns. A type of dart, known as a ballistic bolt, consists of a pointed metallic core with a plastic cover which serves as a sheath to protect the bore from the hard metal core and is shaped into stabilizing fins. These sharply pointed steel projectiles can ricochet and should always be used with great care and certainly never allowed for use by youth. Darts also may present a hazard to the health of a powerful spring piston airgun. Their lightness, and lack of resistance, factors which may be shared with lightweight hard core pellets with plastic sheaths, may provide insufficient resistance to properly brake and air cushion the forward piston impact of a powerful spring piston airgun. Repeated slamming of the piston of such guns can injure seals, pistons, mainsprings, and produce permanent, irreparable damage to the airgun and its scope sight.
A particularly innovative type of airgun projectile was introduced in 1982 in Britain under the brand name of "Sabo®". This is an airgun version of the sabot projectile used in firearms, such as the Accelerator® bullet. The Sabo requires the shooter to use a special tool arrangement to fit a plastic "husk" around a bullet shaped copper plated lead projectile. When the pellet exits the muzzle, the plastic covers fly off and release the slim, aerodynamic bullet within. The maker claimed that this projectile, which must have a much smaller diameter than the bore, but which has as much weight as an ordinary pellet, has greater aerodynamic advantage in the air than the traditional hollow diabolo pellet of similar caliber. Because the projectile is lead, and of normal weight, it does not present the hazards to gun and shooters and bystanders that bay be presented by extra lightweight plastic pellets with steel cores. For field use, the most serious drawbacks seemed to be the somewhat greater cost and the fair amount of manipulation necessary to get a Sabo into firing position. Unfortunately, the patent holder of the regular plastic sheathed pellets took legal action against the Sabo makers and forced their interesting product off the market.
Effects of Repeating Mechanisms:
The nature of diabolo pellets, with their delicate, soft skirts does not lend itself well to most repeating airgun mechanisms. If the repeating mechanism is forceful enough to operate dependably, it almost invariably will damage the skirt of the pellet. If the mechanism does not operate so forcefully, it will probably be undependable. Repeating airgun mechanisms generally are not only harmful to the pellet and/or undependable, but also produce lower velocity, lower accuracy, greater vibration, etc., due to the tolerances needed for handling the pellet mechanically and because of the blow-by of air due to irregular and damaged pellet skirts. Tubular magazines of certain repeating airguns may require pellets with a certain length and head shape for correct feeding. A bluntly rounded or flat-headed pellet is usually required. The better grades of wadcutter pellets also will operate in many repeating airgun mechanisms. Some of the best repeating airguns now have mechanisms which avoid the matter of moving the pellet during operation. These include special cylinders and feed bars with multiple chambers. Many of these operate quite dependably, but accuracy generally is directly proportional to the precision (and therefore cost) of the mechanism. Really fine accuracy does not appear within repeating airguns until the cost of the gun is in the high hundreds of dollars.
Whether pellets are dry or oiled seems to make little difference in performance. Shooters concerned with extreme accuracy generally have found that unoiled pellets produce the best results and certainly dry pellets are much less likely to transfer harmful grit into delicate airgun mechanisms and rifling or to generate diesel firing problems. Spring-piston airguns transfer a small spray of compression chamber lubricant into the barrel with each shot. Other types of airguns may benefit from having their pellets oiled – the pellets may be treated with the lubricant and then allowed to drain dry. More about this subject later.
Testing of Airgun Pellets
Again we come to an area where the world of airguns is quite different from the world of firearms. Most of the world's airgun pellets are still made on first and second generation machines. There is greater variation between different lots of the same pellets, even between some of the very best ones, than the manufacturers would like to admit. Many published specifications on airgun pellets are of limited value. The situation really is quite different from that in the field of firearm where one can simply get a batch of a certain type of commercial bullet and run various measurements which will give you figures that will apply quite well to similar bullets found anywhere in the world. When moving into the airgun field, however, one is moving into an area where tiny differences become major percentages and even the state of the metal can have significant performance effects that would be invisible when swamped by the power of the driving force in a firearm. One can get some indications from testing a given gun with a given lot of pellets, but it is not possible to get the same kind of testing accuracy from small groups of pellets and guns that is possible in firearm testing. Not only do the pellets vary, in a more significant way than equal quality firearm projectiles, but the bore and rifling characteristics can have a considerable effect on velocity, velocity maintenance, and accuracy. Most manufacturers of both pellets and airgun barrels must permit variations within certain limits, which despite the smallness of these variations, may make a gun of one serial number shoot well with a certain type of pellet whereas another serial number of the same gun will not do so well with that pellet. This situation was also observed by the internationally known gun expert, John Walter, who in referring to articles on airgun performance indicated that claims of these articles may be questionable because "the tests prove only that a single gun of a particular make shot best on a solitary occasion with an isolated batch (not brand) of pellet” .Exercises in measuring the weight and measurement of variation of individual lots of pellets may also be of limited significance. As noted before, the really important factors are uniformity of weight distribution, axial alignment, in-flight stability, and the resulting minimal yaw. These factors generally can be tested in a meaningful way only by shooting tests. The very best pellet manufacturers test all lots of their best pellets in actual machine rest guns. In the case of Beeman H&N match wadcutter pellets the pellets are not only individually visually and mechanically inspected by a specialist, but those lots that give the top 20% accuracy in firing tests are segregated for individual packing into foam sheets as their finest grade.
It might seem that testing various airguns with the very same ammunition would be a valid and fair of comparison, but this is not perhaps even generally so. This is because, again in some contrast to firearm testing, different airgun projectiles do not behave the same in different guns. It is only fair to evaluate what a given airgun will do with the ammunition which works optimally in it. It is easier to compare the performance of various projectiles fired from the same gun. As noted, tests of only a few specimens of a given model airgun may have only limited validity. Unfortunately, perhaps the only really meaningful general data can come from those who have the opportunity to test dozens, even hundreds, of the same model under similar conditions. Generally, of course, this would be only the manufacturers or distributors with large volume testing and shop facilities. However, this restriction on generalization shouldn't restrict the individual shooter from the satisfaction and importance of finding out how his own airguns best perform.
Spring-piston airguns simply cannot be considered or tested in the same manner as firearms. It is only natural, since they look and appear to behave much like miniature firearms, that they should be considered like firearms. However, the differences are basic. When one has a series of firearms, all the same model, along with a large quantity of ammunition, of a certain grade and type, one can expect to get quite uniform results between the rifles and between shots in different guns. This is simply not the case with spring piston airguns. First, it is important to carry out the tests with the pellets which are going to give the most favorable and optimum results. For maximum velocity the Beeman Silver Bear or Beeman Laser pellets generally give excellent results.
The chronograph should be corrected to muzzle velocity, rather than reading at the distances of the gates and the velocity figures increased for velocity lost by the penetration of paper if photoelectric screens are not used. Mainspring power variations can result in as much as 10% between different batches in guns of the exactly the same mode. (Example: 10% below 800-830 fps. is 720-747 fps.) Also, there is no way for any of us to have actual average velocities from any gun. We can only have the results of our tests. The results of a ten shot string may indicate a mean average of 758 fps with a standard deviation of 7 fps. That, of course, means that there is only a 68% chance that the true mean lies between 751-765; a 95.9% chance that it is between 744-782, and we're almost completely sure (99.7%) that the true mean lies between 737-789 fps.
We have had Beeman Rl rifles go over 1,000 fps with Beeman pellets, and often go over 1,000 fps with certain lighter pellets whose lack of resistance may even cause piston impact injury to the gun. Gun sellers should not advertise such high or unusual results. What should be presented is what can be expected, on the average with optimal lubes, and optimal pellets.
Commercial production of pellets is primarily by swaging. The shape of the diabolo pellet does not lend itself well to casting, but it is possible to cast some unusually heavy, bullet shaped pellets using some pellet molds. Because of their bullet shape, such pellets have greater friction, but the special shape and extreme weight, and the capacity for being homemade, makes these pellets of special interest to the serious airgun hunter, experimenter, and survivalist. The McGuire pellet mold casts sharply pointed "Spitzer", hollow-base bullet-shape pellets. The .177” (4.5 mm) pellet from these molds weighs 14 grains (0.91 gms.) and the .22” (5.5 mm) pellet weighs 20 grains (1.3 gms.). The best material for casting is melted down pellet lead retrieved from a metal pellet trap. Caution: Melting down pellet lead retrieved from a "silent" pellet trap which utilizes putty or other material to trap the pellets should be done with great caution and only where there is a great deal of ventilation and a fire extinguisher handy. Firearm bullet lead generally has a bit too much tin, zinc, or antimony to be soft enough for airgun pellets, but such material can be mixed with pure lead to make it satisfactory for this purpose. Very light oiling of these bullet style pellets probably is advisable.