Posts Tagged ‘parallax’

Some scope fundamentals: Part 2

by B.B. Pelletier

Part 1

This is one of the most popular reports I’ve done in a long time. That may be because scopes can be very cantankerous to deal with — hard to mount, difficult to zero, always seem to shift their zero, etc. Today, I’ll address some of the problems you can have and some ways to minimize them.

Scopes should work — no?
To the non-shooter, the telescopic sight seems like a guarantee of accuracy. We’ve all seen the movies. Put the crosshairs on the target, squeeze the trigger and you can’t miss.

Then, you try it for the first time, and you notice that you can’t keep the scope’s reticle (crosshairs) steady. As long as you hold the rifle, no matter what you do, the crosshairs move. Each beat of your heart makes them jump a little. Each breath you take in can move the scope or at least tilt it. You can minimize these movements through training, but nobody can eliminate them entirely. That’s why I shoot from a rest so often. But sometimes that doesn’t work — especially with spring-piston airguns. You have to learn the artillery hold; and since that technique goes well beyond what many people think, I’ll explain it more fully here.

Relax for a neutral hold
The artillery hold is really just a way to get you to follow through, but there’s more to it. An important part of the hold is how you are at the instant the gun fires. You have to be completely relaxed, so the gun doesn’t recoil back and encounter an off-center obstruction that shifts the muzzle in a certain direction.

Here’s how to achieve this relaxed state. After putting the crosshairs on your target, take a breath and expel most of it. Try to relax as you do this. The crosshairs will usually move off the target in a certain direction. If you had fired before relaxing, the pellet would have gone off target in the same direction the crosshairs just did. Maybe it wouldn’t have gone quite as far as the crosshairs seemed to, but it would have moved in the same direction. The result is a larger group.

Let’s try again. This time, after you relax, move the crosshairs back on target by shifting the gun or your hands slightly. It doesn’t take much.

Once you’re back on target, take a deep breath, close your eyes, let out most of the air and relax again. Now, open your eyes and see where the crosshairs are. They probably moved again, only this time they didn’t move so far. Shift things to get back on target again and repeat this procedure.

You may have to repeat this procedure several times before the crosshairs are still on target when you open your eyes. When they are, you can take the shot — making sure that you allow the gun to recoil and move as much as it wants to. This time, the shot should feel very different than it normally does. It should feel neutral — as though you’re no longer connected to the gun. That’s the feeling of a perfectly neutral shot and one that will group as tightly as the gun is capable of — if you can repeat the process several times.

What does this have to do with scopes? Everything! This is the only way to shoot a recoiling airgun with any accuracy; and until you can do that, you’ll never have much success with a scope.

With most firearms, except .22 rimfires, the hold isn’t nearly as important for accuracy because the bullet is out of the gun before all the movement takes place. But with airguns, and especially spring-piston airguns, the pellet hasn’t started to move before the gun does. Only a .22 rimfire is similar, and even they’re much more forgiving than most airguns.

However, you do need to know that all firearms are affected by hold, as well. Even centerfires that shoot in excess of 3,000 f.p.s. will benefit from the hold I’ve described here, but the amount of accuracy increase is so small that it’s only of interest to target shooters and long-range varmint hunters. The average shooter won’t normally notice the difference between a 1-inch group and a 1.25-inch group at 100 yards. Or if they do, they won’t care. I’ve heard that from so many shooters at my rifle range over the years that I know it’s true.

Now you’re ready
If you can learn how to neutralize your rested hold using the process I just described, you’ll see an immediate increase in accuracy from your scoped guns. Then, you’re ready to discuss scope fundamentals!

Temperature is critical
We don’t appreciate how sensitive a modern telescopic sight can be. I don’t mean fragile, either — I mean sensitive. Every change in temperature changes the point of impact of your scope a little. No scope is immune to this phenomenon, yet most shooters act as if once the scope is zeroed it stays zeroed.

Field target shooters know different. I’ve seen a field target scope with three different sets of click values on the elevation knob, each color-coded to a 20-degree temperature range. The shooter who owned that scope took the time to not only figure out all the elevation click values for every yard between 10 and 55 — he did it three separate times when the temperature was in three different ranges! That’s something Hollywood will never show you.

The optical elements inside a scope are refracting light to the millionths of an inch. When they move in relation to one another — because the metal tubes that hold them expand and contract from changes in temperature, the light beams do move. The movement is very slight, but it can and sometimes does change where the images appear. The point of aim changes.

There are many other reasons for a shift in the point of aim, but temperature is a constant one that must always be taken into account. If you’re looking for the way to prevent such changes, I’m sorry to disappoint you. There’s no solution to cancel the effect of temperature changes on a telescopic sight. But if you know it will happen you can at least anticipate it and adjust your scope when the time comes.

There are so many different kinds of scope reticles that it would take a book to cover them all. And most of the highly specialized ones are for specific purposes, such as the ballistics of a single military round, so they have no place in a general discussion. I’ll address hree general types of reticles found on most scopes. If I miss something, you can bring it up in the comments.

The oldest type of reticle is the plain “crosshair,” which is two straight lines — one vertical and the other horizontal. In some scopes, these lines actually appear to move as the scope is adjusted, but that’s getting pretty rare today. More often, the crosshairs remain in place in the center of the image and the adjustments move the whole image, so you don’t notice anything.

The plain crosshair is the oldest type of reticle. This image shows thick reticle lines, but they can be much thinner for greater aiming precision.

Often a very thin reticle can be difficult to see against a background, so there will be a small dot at the center of the crosshairs that makes them stand out. This dot will be small, perhaps one or two minutes of angle (a minute of angle covers about one inch at 100 yards), but it doesn’t take much to be noticeable against anything but a dark woods background.

This dot looks large on the heavy reticle lines. But in many scopes, both the dot and reticle lines are very small and fine. This is just for illustration.

Plain crosshairs are best in open country and are therefore favored by long-range shooters. They’re fine for plinking, as long as the reticle lines aren’t too thin. They’re less useful in deep forests, where the reticle lines don’t stand out. For that terrain, probably nothing beats the duplex reticle.

The duplex reticle is a plain crosshair that has thicker lines near the edges of the field of view and thinner lines in the center. When I shot field target, I used a scope with a duplex reticle for two reasons. First, it was much easier to see in the deep woods where many matches are shot; and second, the duplex offers four additional aimpoints.

The duplex reticle uses crosshairs of two different sizes. The ends of the thick posts provide four additional aim points that can be used for things…like greater or lesser distance and wind.

Duplex reticles are the favorite of hunters, because they work well in deep foliage yet they permit precise aiming at the same time. Like plain crosshairs, duplex reticles come in different thicknesses.

In the mil-dot scope, the dots are an exact size (measured in mils) and are spaced apart an exact distance. On variable scopes, they must be used at one power setting to work as designed. Read the information that comes with the scope to discover how this works.

Mil-dot reticles are a more recent invention. They feature dots of a controlled size spaced along one or both reticles at regular spaces. Mil is short for milliradian, a measure of angle that, unfortunately, has never been standardized. Or perhaps it’s more correct to say that it has been standardized dozens of times — each with a different measurement. When I was a mortar platoon leader, our fire direction center and mortar sights used the old French measurement of 6,400 mils to a circle, but there are many other measurements that differ — some slightly and others in a more significant way.

One common use for the mil is rangefinding. Though it isn’t exact, we say that one mil subtends (covers) one meter at 1,000 meters. At 100 meters one mil subtends one-tenth of a meter or 3.9 inches. That’s so close to 4 inches that we round it up.

A whitetail deer is about 12 inches from the top of the shoulder to the bottom of the chest. A two-mil dot will just about cover the deer’s chest at 150 meters.

Is that too much for you? It is for many hunters who still use the mil-dot scope for aimoff when there’s wind. Or they use the vertical dots for aim points at distances other than the range for which the scope is sighted.

Focusing the reticle
The first thing a shooter must do with a scope is focus the reticle. The eyepiece should adjust to allow you to do this, and it does on all but the cheapest scopes. Focus by looking through the scope at the sky or a light-colored wall and turn the eyepiece until the reticle appears in sharp focus. I’ve read that this is supposed to be done incrementally; because if you stare at the reticle very long, your eyes will naturally focus on it. So do it in stages.

After you focus the reticle, some scopes have a locking ring to hold that focus. Others don’t have the locking feature, but the focus rings should be stiff enough to hold your focus without it.

Focusing the reticle is very important for scopes with adjustable objectives, because the scope’s designers assume the scope is in sharp focus when the objective ring or sidewheel is turned. Only when the reticle is in focus will the scope come close to the distances marked off on the parallax ring or knob, which is the adjustable objective we are discussing. And, of course, that will also depend on the temperature when the scope is used.

On the other hand, on lower-powered scopes that have a fixed parallax setting you can use the focus to bring close targets into better focus. This isn’t what the adjustment is for and it will blur the reticle somewhat, but sometimes it’s the best way to use a low-priced, fixed-focus scope at closer distances than it’s intended.

Some scope fundamentals: Part 1

by B.B. Pelletier

I’ve noticed that a lot of you are responding positively to the fundamentals that have come out in some of the recent reports, so I thought I would do a few more important ones for you, starting with scopes. This will be a series of bite-sized reports.

My experience shooting the Conquest with a 4x scope at 50 yards last week and getting great groups prompts me to want to share a number of scope evaluation tips with you. And, as always, I expect the comments from our readers are going to be even more interesting than the reports.

What magnification (power) to choose?
Starting with the Conquest accuracy test, it’s obvious that you don’t need a lot of magnification to shoot well. I normally use more than just 4x for a gun as accurate as the Conquest, but not on all rifles. As a scope increases in power, it also gets longer and heavier, so a compromise between power and size is usually best.

I have some 3-9x scopes that have unusually clear optics and thin reticles that I enjoy using. Of all of them, the one I like the best is not marked in any way. I think it’s a Leapers, but there are no identifying marks that reveal who the manufacturer is. The optics are clear and the crosshair is thin and sharp. This is often my go-to scope to use for a quick test.

My favorite power combination is probably a 4-16x. I find it packs the most power into a convenient package without the scope becoming too long and heavy. Given today’s optics, a good 4-16x isn’t much longer than a 3-9x from a decade ago.

But you don’t need even 16x to shoot accurately. That is what the new airgunner must understand. I have a .250 Savage centerfire rifle that shoots 10-shot groups smaller than one inch at 100 yards nearly every time. The scope on that rifle is a vintage all-steel Weaver V9 W, which means it is a 3-9x variable that has a wide field of view. The objective lens is only 32mm, so it isn’t as bright as some modern scopes, but it has a super-fine reticle with a tiny dot at the intersection of the crosshairs. If I ever find another scope like this at a gun show, I am prepared to buy it because the combination of power, optical clarity and crosshair size is ideal for this rifle. I use this rifle for prairie dog-sized targets out to 300 yards. That’s good enough for me.

Another rifle that shoots small groups is a custom No. 5 SMLE that I’ve converted to .219 Donaldson Wasp. The scope on this one is another one that’s vintage and all-steel — a Redfield 2-7x variable with what appears to be a 28mm or 30mm objective. The crosshairs are even finer than those of the vintage Weaver, and the dot at the intersection is also smaller. This rifle should be good for prairie dogs out to 300 yards, as well, but I feel the power of the scope limits the range to 250 yards for targets so small. Coyotes to 300 yards are possible because they’re much larger. So, I’m saying that a 7x scope works well at 250 to 300 yards, but the maximum effective distance depends on the target — at least for me.

It might be an ugly rifle, but this .219 Donaldson Wasp can shoot. It has a custom Shaw barrel of my own design with a faster twist. And the little Redfield scope is plenty good for what I want to do.

Going the other way, I absolutely love Leapers’ line of long eye relief scopes that produce 1.5-4x. These scopes may not make the target appear large, but they can’t be beat for clarity. For value, I don’t think the Leapers 1.25-4×24 long eye relief scope with the one-inch tube has any equal. It’s currently priced at only $85, which is very little for such a great sight. It would be ideal on big bore airguns of all kinds, as well as powerful springers that won’t be shot past 50 yards — rifles like the Beeman R1 in .22 caliber, for example. Yes, the parallax is set at 100 yards, but I have found that when the magnification is this low, it doesn’t matter where the parallax is set. This scope would be ideal on a New England Firearms (NEF) single-shot rifle in .45 Colt or .44 Magnum or on any small carbine in a pistol caliber.

What about more powerful scopes?
There are a FEW applications for the scopes with power up to 32x and more. Field target competition is one such game — not because of the additional aiming precision, but because that extra power helps you resolve small objects out at 55 yards, so you can determine ranges with the parallax adjustment more precisely. When you can focus on very small objects at long distances, the scope helps to determine the range to them. And long-range target shooting is another time when a higher-powered scope is needed. When you’re going for the absolute best group that can be fired from a gun, the scope must be powerful enough to reduce the aiming error to the smallest fraction of an inch.

Talk all you want about big scopes. Try carrying around one like this for a couple hours! A Daystate Harrier is dwarfed by this monster Tasco Custom Shop 8-40×56.

HOWEVER — and this is the whole point of this discussion — it doesn’t take the Hubble Space Telescope to shoot good groups at 50 yards. As you clearly saw in my report on the Conquest, I did it with only 4x. Consider that when thinking of your next scope. You can have a handy package that carries easily and handles rapidly or you can mount the biggest bragging-rights scope money can buy on your air rifle and then suffer for it.

Clarity goes hand-in-hand with accuracy when using a scope. In fact, I think clarity is the single most important attribute a scope sight can have. There are technical means of determining relative clarity in scopes. The most common one is determining how many line pairs the scope can resolve in a standard test. Clarity is actually a statement of the scope’s ability to resolve an image. When we say clarity, we mean resolution.

I am not an optical engineer, nor am I qualified to discuss how scopes are tested. And the subject is so technical that even if I could discuss it, not everyone would understand what I was saying. I’m going to reduce the resolution/clarity question to something we can all understand.

I have a simple test I use to subjectively determine the relative clarity of a scope. All I do is point the scope at the roof of my neighbor’s house about 25 yards distant and look at the shingles. If the shingles appear sharp, with the vertical joints well-defined and the abrasive particles standing out clearly, I know the scope is clear. If any of the image is muddy, even after the scope is adjusted for that range, I know the scope is not as clear as I would like it to be.

I developed this test a couple years back when I pitted a Hawke scope against a Leapers scope of the same power and specifications. Until that test I thought nothing affordable could ever beat a Leapers scope; but in that test, the Hawke scope emerged as the clearer sight. It was also more expensive, but it didn’t cost twice what the Leapers did, as I remember. The shingle test is a good one for any scope you intend using for target shooting or hunting, as nothing in the field will exceed the fineness of the image the shingles can give.

If you don’t have access to shingles, anything with a fine grain will work just as well. Old wooden fences are another way of testing the resolution of your scope. Just be sure to always test every scope at the same distance and using the same object, and your test will soon become very refined.

When you buy a scope, you usually can’t perform the test I just described. You have to take someone’s word on the clarity. But I have a couple tips about that.

1. Multi-coated optics on inexpensive scopes are usually not as clear as single-coated lenses. Leapers has used a single coating of emerald for as long as I’ve known them, which is why they’re as clear as they are at such a low price. You might give up something else with single-coated optics, such as five minutes hunting time in the morning and evening, but that depends on what kind of coating it is.

This deserves an explanation. While multi-coatings can be applied to make optics perform their best, the hype of multi-coating is too powerful to be overlooked by the marketing departments of many manufacturers. Therefore, the cheap scopes are multi-coated without regard to light transmission or any other enhancements. As a result, these multi-coated optics are much like airguns that shoot over 1,000 fps — lots of hype but you’re giving up accuracy. On the other hand, expensive multi-coated optics deliver superior performance.

2. The objective size doesn’t matter as much as you think. You don’t always need the 56mm objective to see clearly. The quality of the lens material and the optical coating(s) matter more than the objective size.

3. A 30mm scope tube will be noticeably clearer than a one-inch tube, if all else is equal.

4. You can live with a lower-power scope if it’s also clear, but a high-power scope that doesn’t focus or is unclear is the worst headache imaginable.

The bottom line
Considering just these two subjects — power and clarity — shop for a lower-power scope with a 30mm scope tube and a single lens coating. From what I saw in the Leapers booth at this year’s SHOT Show, there will soon be a flood of very clear scopes at good prices (but not cheap!) hitting the market this year.

Stop shopping for scopes by price, alone, and then condemning your rifles, pellets and the entire hobby of airgunning when things don’t work out! Most cheap scopes are cheap for a good reason. I understand trying to buy the best scope you can afford, but stop focusing on the price so much.

Cheap scopes aren’t usually that much worse than more expensive scopes. I say “usually” because I’ve seen a couple brands that can be counted on to be bad. But cheap scopes don’t pass through the quality controls that most of the more expensive scopes do. You’re far more likely to end up with a lemon if you buy the rock-bottom scope.

And this final tip is worth the price of this entire blog: Most combos (rifle and scope for one price) that are put together by manufacturers are put together by their marketing departments to get rid of the cheap scopes nobody will buy! However, when a combo is put together by a dealer, that usually isn’t┬áthe case. Pyramyd Air has put some very decent scopes on some of their combos because they realize their customers really care which scope comes with the gun. The more the combo costs, the better the scope will probably be.

But watch out for those manufacturer combos!

Ruger Air Magnum Combo – Part 3

by B.B. Pelletier

Photos and testing by Earl “Mac” McDonald

Part 1
Part 2

Hopefully, I’m getting this test finished in time for a few last-minute buying decisions for the holidays. I’m sorry it takes so long, but time being what it is, it’s the best I can do without turning this blog into an infomercial.

Today, we’ll look at the accuracy Mac was able to get from this powerful new ├╝bermagnum spring rifle. I know many of you were predicting it wouldn’t be very good, given the power output.

This is also the day when Mac will show you how to adjust the parallax of a fixed-parallax scope so you don’t have to buy a new scope to get what you want from the gun. Since that’s an interesting procedure, let’s do that first.

I was exposed to this trick back when I shot field target. Many shooters were changing the parallax on scopes with fixed parallax back then.

Simply unscrew the trim ring on the end of the objective bell.

Step 1. Remove the threaded trim ring on the objective bell. On this scope, you’re lucky, because that exposes a cross-slot on the objective lens unit that lets you insert a thin screwdriver blade. Because of the wide span that must be crossed, a thin knife blade is often the best tool for this job. By turning the objective lens assembly slowly in either direction, the entire objective lens assembly can also be turned.

Step 2. To adjust the scope for a different range, turn the objective lens assembly while checking the sharpness of the focus on an object set at the range you wish to adjust to. Turning this assembly out adjusts the focus closer — and in moves it out farther. Unless you completely remove the objective lens assembly from the scope, no nitrogen will be lost, as the extremely viscous grease on those fine threads perfectly seals the inner part of the scope. If the seal is broken, though, the scope will be compromised and will fog up unless it’s resealed.

Just get some kind of spanner (a thin knife will do) and turn the objective lens assembly in or out.

Step 3. Once you’re satisfied the scope focuses where you want it (i.e., the parallax is set where you want it), replace the beauty ring to lock the objective lens assembly. The job is now done.

Mac tells us that the rings that come with the rifle are nice and appropriate. They have four screws per cap and each ring has friction tape inside to prevent scope movement. Don’t do what Kevin said someone did and remove the tape because it doesn’t align quite right. Keep your hands off that tape! It’s there to do a job; and if it’s removed, the hole through each ring gets bigger.

Mac noted that the nameless scope seemed to be adjusted for the 30 yards he was shooting, so there was nothing more to do but sight-in. As first tested, the rifle shot just two inches low, with no noticeable left or right deviation. That little amount is what the scope knobs can do by themselves, so there was no need to adjust the scope mounts in any way.

Next, Mac started the testing with some Crosman Premier 10.5-grain pellets. Ten of those grouped into a pattern that measured 2.7 inches at 30 yards. Mac calls this poor, and I have to agree.

Ten Crosman Premier heavies went into 2.7 inches at 30 yards. Not a good group.

Next, he tried 10 RWS Hobby pellets that we all agreed are too light for this powerplant. They held 9 in a group measuring 2 inches even. A tenth shot was a called flier that missed the target paper altogether. This is another pellet not to try.

Except for the called flier, these RWS Hobbies grouped better than the heavy Premiers, but notice the dark edges of some of the pellet holes. Clearly, this pellet is wobbling on its way downrange –something that can’t be determined from the less-precise holes of the Premiers.

Then, Mac loaded 10 JSB Exact Diabolo heavies, the 10.2-grain domed pellets that often work best in powerful air rifles; and, again, they did their thing. They gave a 10-shot group that measures 1.1 inches at 30 yards, which is acceptable hunting accuracy.

Finally, a good pellet gives Mac what he was looking for. This is a 1.1-inch group of 10 JSB Exact Diabolo 10.2-grain pellets.

Just for the record, Mac also fired 10 RWS Superdomes and 10 RWS HyperMAX pellets at the same distance. The groups from both pellets were too poor to measure. We know that the 5.5-grain HyperMAX pellets were traveling over 1,400 f.p.s. and could not be expected to be accurate. But, why were the Superdomes also a problem?

RWS Superdomes are almost pure lead, plus their skirts are very thin. In a rifle shooting 800 to 900 f.p.s. that’s perfect, because the rear of the skirt blows out and seals the bore behind the pellet. But, in a powerhouse like the Ruger Air Magnum, it shoots them well above the sound barrier. The thin skirt is blown all the way out until the pellet resembles a cylindrical can with a slightly domed top. Since the wasp waist is where the accuracy comes from, it’s not good to lose it this way. The pellet is then free to fly wherever it wants, destroying accuracy. If Mac could recover some of these pellets without damaging them, that is what we would see.

But, that doesn’t matter, because Mac has found a good pellet for the rifle. Putting 10 shots into 1.1 inches at 30 yards is certainly good enough for hunting. At this power level and price point, I think this is one spring gun you’ll want on your short list.

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