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Airgun Ammo & Airgun Facts > !Airgun Facts -a worthwhile read!



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Bullet velocity and other lies
When browsing the web, reading airgun ads, or consulting catalogs, you will most likely stumble upon claims about bullet velocity of certain airguns.

Velocity, however, is never a reliable gauge for power, though one is often under the impression this is exactly what is suggested.

Bullet velocity is linked to bullet weight. Both in conjunction define energy. The higher the weight, the higher the energy. Twice the bullet weight at a given velocity means twice the energy; it's linear.

However, since calculating the kinetic energy is done by raising the velocity to the second exponent, twice the velocity will result to four times the energy; four times the velocity to sixteen times the energy, etc.

A rifle advertised to shoot 1000+ foot per second will perhaps just be delivering 875fps when chronied. Not all shooters have a chronograph at hand, so the question why never arises.

875fps, however, might still be very good. The manufacturer chronied the most powerful in a batch of one thousand guns, using the lightest available pellets. One single chronied shot out of 100 was 1002 fps, which made them feel entitled to claim that the gun shoots 1000+ fps. It does neither reflect the average velocity of those other 99 shots, nor does it reflect the average velocities of the other 999 guns. In fact, it does reflect just about nothing at all, since there is never any declaration of the slug weight either.

Another aspect of this overrating is product liability. The manufacturers try to avoid lawsuits where claims are made based guns that are more powerful than officially stated.

When you chrony the gun, you are most likely using heavy pellets such as Barracudas - those that group well - while the manufacturer may have used ultra light ones such as the Lasers. Light pellets practically never group with powerful guns, which renders that combo useless. The reason is that they are too fast, becoming aerodynamically unstable in supersonic velocity ranges.

The all important thing to keep in mind is that velocity figures mean close to nothing.

But since shooters are eager to talk about velocity all the time, not alone the manufacturers are to blame if they try to present their products in the best possible light, or are they?

Kinetic energy instead, usually measured in foot-pounds or Joules, is a reliable and relevant gauge to measure the power of a firearm.

Another great example of twisted truth is accuracy claims. Any gun producing 2 MOA - yes, 2 MOA, not 1/2 - must be considered pretty accurate. That means it places bullets within a 1 inch diameter at 50 yards;sufficient for hunting purposes. The majority of shooters will be out shot by such a gun anyway. 1 MOA is very, very good, while 1/2 MOA is world-class accuracy.

If this statement puzzles you, I am talking about reproducible accuracy over hundreds of rounds, not just 3-shot groups, then picking the best for publish.

Look out for indications about the distance, and then if that distance was accurately measured, or if it was just estimated. If it was measured, was it tape-measured, or measured using a range-finding scope? There is a common tendency to way overestimate distances in the field, when done by eye. The accuracy results shown on the range page qualify under these terms.

In summary, it helps to look critically at accuracy claims, otherwise you may feel bad that you cannot shoot half-inch groups at 50 yards all day long - offhand of course - like all the other fellows on the message boards.

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Pellet shapes
As the diabolo shape is the possibly worst design imaginable with regard to aerodynamics, I dare to claim that it does not make much - if any - difference what shape the pellet's head is. Its ballistic coefficient may very well be neglected as well. Use the pellet that prints the best groups.

Consider that most diabolos become increasingly unstable at velocities 1100ft/s and above. Some, like those with pointed heads, might become unstable already at 700ft/s.

An indicator to corroborate this hypothesis is that a lot of powerful guns usually do not group well using light (fast-flying) pellets.

Click the picture on the left to view the true 1000ppi scan of those .22s.

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The best caliber
Bullet weight and caliber makes a big difference with regard to efficiency, often referred to as "killing power", while velocity is of no significant relevance, at least not in the range of subsonic velocities. As the heavier .22 is initially slower at the muzzle than a .177, air resistance will be significantly lower and it will not slow down as quickly as its swifter sibling, although the diameter of the latter is greater. Thus it carries more energy over distance. Also, with regard to efficiency, the .22 is superior as it prints bigger holes. The .20 caliber is good for shooters who like to make compromises; a little bigger pellet than the .177 and a flatter trajectory than the .22.

One common misconception is that bullet weight has an influence on trajectory. Although in practice this seems to be correct, the statement is not to the point. It is rather the time of flight that really matters, not bullet weight. A 20gr projectile flying at 900ft/s will have the exactly same bullet drop as a 7 gr. projectile flying at 900ft/s. At least in theory, that is. In a real-world scenario, the .22 will have less deformation caused by by the lands and grooves, and might therefore be aerodynamically more stable.

With almost all airguns, the point blank range of cal .177 is greater than that of .22. This means that if you have zeroed your rifle at a given distance, you can reliably hit the target at other distances without modifying the point of aim.

There is an ongoing controversy of which caliber is best. I do not engage in this discussion, since there simply is no right or wrong answer. The .177 has a flatter trajectory; the .22 has a greater punch. I can only give recommendations that are based on my personal preference: for the use of hunting, if bullet energy is in the range of 18 foot-pounds or greater, there is no reason to use anything smaller than .22. For guns producing the somewhat limited energy of 12 foot-pounds, I recommend .177.

Velocity alone as a factor adding to the killing power is hardly of any significance, since most airgun projectiles are subsonic, or, at 1100fps, just slightly above. Velocities that low do not produce shock in vermin, as opposed to centerfire projectiles flying at 2600 fps and above.

With regard to (field) target shooting, there is (almost) total agreement among shooters that there is no point in using anything else than .177, simply because of the flatter trajectory.

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Choked accuracy barrels
Only choked barrels deliver superb accuracy, though there might be the odd exception.

The reason is as follows: the length of the barrel or how straight it is has no measurable influence on accuracy. It's only the last few inches that count; the pellet must exit the barrel exactly the same way every time. That is where the choke comes in. The last one or two inches near the muzzle have a slightly smaller diameter than the rest of the barrel. This, in effect, calibrates each pellet to exactly identical measurements, right before it exits.

Choked barrels can be expected to be less pellet-sensitive, as pellets from different makes are likely to have different diameters.

You can easily test if a barrel is choked by pushing a well-fitting pellet all the way through the barrel, using a cleaning rod; from receiver to muzzle. About 1 inch near the muzzle, you'll feel that you need to push significantly harder. Sometimes a second choke is also located near the breech.

Of course the barrel could be super-tight all the way down, but that would cause more friction resulting to a lower muzzle energy. It might also cause more lead-deposit. Optimal is as as little friction as possible (but maximal air-tightness) for the non-choked areas.

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Rifle scopes - making the right choice
You hear a lot of stories about magnum springers eating scopes, and there certainly is some point to that. The two-way recoil working on the scope is tremendous.

However, most shooters experience problems with cheap or cheapest bargain scopes that can simply not hold up to the task.

I advise strongly against installing any of those cheap "airgun" or "rimfire" scopes as most of them are likely to break, often their reticles. Unfortunately, this is where most shooters think they can save something, and it seldom works. It's just a waste of time and money.

A quality scope instead is hardly ever a problem on those guns. Don't try to save on the scope and/or mount.

The whole rig must be heavy-duty!

Also, one of the requirements is parallax adjustment from 10 yards to infinity. Most centerfire rifle scopes are parallax-preset from 100 yards (or meters) to infinity, so what is the minimum distance for those scopes is your airgun's maximum range. Those scopes are not suited. Also, keep in mind that some are not designed to take the double-recoil. The hard snap comes from the opposite direction.

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Rifle scopes - mounting them and other obstacles
Anyone can tack a scope onto a rifle and hope for the best. Doing it expertly, however, is often way more tricky than just finding the right Allen key. Among the many things that can go wrong are...

Improper sighting-in: extensive adjustment of both windage and elevation is a no-go for a number of reasons, true even for high-quality rifle scopes; bad sight picture and a shifting POI on changing magnification. Plus there might not be enough room left for further adjustments. If properly sighted-in, the elevation and windage adjustments are centered and the POI is roughly on target. Often, shimming or/and grinding the mount rings is required. However, when doing this extensively, epoxi-bedding the scope tube is recommended, otherwise cant might be induced which will stress the scope tube, instead of supporting it.

Take a look at a customized mount in progress.

Cant: the crosshairs are not perfectly adjusted horizontally/vertically; adjusting the windage will also shift elevation and vice versa. Pretty annoying.

Zero shift: May be caused by a number of reasons, sometimes almost impossible to tackle down.

Scope creep: we have come to known that one by now! On springers, the violent forward snapping is very much as if you'd hit the gun with a 3 pound hammer on its butt. To prevent scope and mounts from creeping backwards, the scope mount bases must be secured with arrestor pins. The scope tube is embedded into the clamping area using a high quality double-sided sticky tape that does not deteriorate with age. This way, the scope cannot move within the rings, and there is no need to tighten the ring screws until the Allen key bends. There is always the risk of accidentally over-tightening the clamping screws and crushing the scope tube.

Crushing the scope tube: Not recommended. (To put it mildly.)

Wrong eye relief distance: the optimal eye relief distance is usually the width of a hand. If the distance is not correct, you will get a poor sight picture. If it's a recoiling rifle and the relief distance is too short, there is a risk of injuring your shooting eye.

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Replacing the piston seal
It is strongly recommended to replace the piston seal frequently, as worn out seals are often the cause for broken scopes or loss of power.

Our red high performance piston seals fit many RWS guns.

- Remove the old seal using a knife.
- Warm the new red seal in hot water to make it temporarily softer. Do not boil.
- Dry the seal, put it on a plate or even floor face down, then press the piston using all your weight with a rotating motion into the seal. If you have access to a drill press, clamp the piston rod into the chuck and while pressing it into, rotate the piston by hand.
- smear a film of moly or sythetic grease (e.g. teflon-based) on the outer walls of the piston and seal. Avoid getting any grease in front of the piston, as this will cause dieseling (combustion of oils and greases within the chamber).
- Note: the material we use is self-lubricating; no maintenance or oiling is required. Never pour oil into the chamber, not even half a drop. Some grease splatters from the piston to the chamber walls on each firing cycle; the cocking stroke then wipes it off, leaving an evenly distributed thin film of grease on the wall, which ensures a controlled combustion.

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Barrel cleaning
High-powered springers do not benefit from having their barrels cleaned using cleaning felts. Doing so is very much like dry-firing, even if loading 2 or 3 felts at once!

Use a brass or aluminum cleaning rod instead and carefully clean the barrel every 500 to 1,000 rounds, depending on pellet type and leading. Use felts only, not any brushes. By all means take care not to damage the muzzle crown. If possible, insert the rod from the breech side.

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The best zero-in distance
For hunting purposes, air rifles are zeroed-in best at 30 meters or 35yards, rather than 50 yards, or 50 meters.

The shown flight path chart plotted by a ballistics program (muzzle velocity of 800fps) clearly illustrates why: the horizontal white line is the line of sight. Now take a look at the blue trajectory which has its primary zero at 50 yards, while the secondary zero is roughly at 12.5yds. In between, the bullet rises over 1 inch above the line of sight; requiring to hold under at all distances between 25 to 45yds. 12.5yd is too close to be useful, so only 50yd is the distance where you hit at what you aim. The point blank range is pretty narrow, since the bullet drops significantly after that distance.

The red trajectory path shows the same velocity at a primary zero of 35yds. The point blank range - the range where you need not modify your point of aim - is now much more extended, ranging roughly from 18 to 40yds! Should the need for a longer range shot arise - 50yds or beyond - you need to hold over a certain amount. Mil-dot reticles are optimal, since they provide several aim points.

Some shooters use the technique of dialling-in the distance, but this practice is only useful for field target shooting. For hunting, one usually doesn't have the time to fiddle the scope's elevation turret.

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Recoiling guns
One of the biggest drawbacks of the spring piston system is its double recoil. When the spring-powered piston is released, it accelerates forward, thrusting the rifle backwards similar to a powder gun. However, before this feeling of firing becomes apparent, the piston bangs into the front end of the compression chamber, causing to stop the rifle's backward movement abruptly, making it violently snapping forward. This also causes the dreaded scope creep, if the scope mounts are not constructed in a way to prevent this.

Unfortunately, all this moving happens while the pellet has not yet left the barrel. In fact, at the time the piston hits the front end of the pressure chamber, the pellet has just started to move. The time interval from the piston release to the moment the pellets starts to move in the bore is called the lock time. As airguns have a much longer lock time and barrel time than powder guns, it is not hard to understand why it is more difficult to hit accurately with them.

Indeed, this double-recoil is often the cause for great misses. The way the rifle is held; the spot where it is hold, and, how much tension is in your muscles holding it on aim, all those variables greatly affect the movement of the rifle during the firing cycle and therefore the impact point. Some airguns/shooters experience a different POI as much as 4 inches at 35 yards when changing the shooting position! Even after a lot of practice and ten thousands of rounds, you might still not master your gun.

A technical solution to deal with this two-way recoil problem is a recoil absorbing system like the one in those rifles you see on this site. The action is moving backwards during the shooting cycle, thus eliminating 95% of the stock's movement. Such rifles are much more forgiving with regard to human error.

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Terminal ballistics
There is little or no doubt a hollow point pellet has greater efficiency, often referred to as "killing power", than a flat-nosed wadcutter, but - only if it expands. No pellet significantly does when hitting with below 4 ft/lbs. Remind you that terminal velocity can be less than 50% at 35 yards and longer ranges.

Other than that, the size of the inflicted wound is significant, at least with regard to air gun pellets, flying close to or only slightly above the velocity of the sound barrier. The bigger the caliber, the more killing power the pellet will have, even if the kinetic energy is the very same.

 

 

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