How to mount a scope: Part 5
by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- More scope stuff
- Swap the rings
- Spiraling pellets
- What to do about spiraling pellets
- Misaligned scope
- How to correct the misaligned scope
- Setting up a rifle
- BB did NOT say all bundled scopes are bad!
- Scope stiction
- Sighting-in for one distance
More scope stuff
While we are finished with mounting a scope, there is more to tell. A lot of it does come to the forefront when you mount a scope, so it is germane to this discussion. We have touched on some of it before, but today I hope to tell you how to deal with it.
Swap the rings
This is a trick that can help resolve many of the problems we will see today. It’s also one of the big reasons that I prefer 2-piece rings to 1-piece. Someone asked last time what can be done when the scope’s axis is out of alignment with the barrel. Well, that is often the case. The way you find it out is — after you sight the rifle in you try to shoot at different distances and discover that your pellet is off to one side or the other. What can be done?
If you have 1-piece rings you can sometimes remove them and turn them around, so the ring that was in the rear becomes the front ring. I say you can do this only sometimes because you may be scoping a recoiling spring-piston rifle and you need the scope stop pin that’s built into one end of the mount. If that’s true you can always install a separate scope stop, but that pushes the whole scope mount forward and what does that then do to your eye relief?
With 2-piece rings you can make the same swap as the 1-piece, plus you can also turn either ring around — or both! We like to think that our scope rings are perfectly bored and aligned with their bases, and that’s often true, but when it isn’t it makes installing a scope a lot more difficult.
Do pellets spiral as they travel downrange? I have seen them do it as I watched the target through a scope. I had bright sun behind me to reflect off the pellet skirt when this happened.
The pellet is traveling down range in a spiral path. Their movement is not caused by the wind. I ruled that out because of the tightness of the groups and because the wind was under 3 mph on the day they were shot. That leaves spiraling as the most likely culprit –- assuming I am right in my suspicions. For the sake of discussion, let’s say I am right and the pellets are spiraling.
This graphic portrays a pellet that spirals as it travels downrange. Even if you don’t see it through the scope you can see the results of it in the groups that are shot.
The only thing I can think of that would cause spiraling is an unstable (yawing) pellet that precesses around its axis in the direction of the spin. If you have ever seen a washing machine become unbalanced on the the spin cycle and hop around the floor in a certain pattern, you have witnessed the phenomenon of precession. Or, watch a top as it runs down.
It has been known for over a century that bullets can precess. I believe it was discovered very shortly after elongated bullets were first used in rifled barrels. Years ago, I read an article in The American Rifleman about a test on the brush-bucking ability of a .30 cal. bullet. Once stability was disturbed by a stout branch, the bullet began to precess in the direction of twist in an ever-increasing spiral. Of course, that test is not the same thing that I’m discussing here, as the instability there was induced mechanically down range by the bullet striking a broomstick rather than yaw at the muzzle and differential air pressure. But it does show that bullets can travel in a spiral path.
Bullets (and pellets) can also be made unstable by their twist. Varmint shooters are aware that thin-jacketed bullets have been known to explode in flight from the centrifugal force of their spin. And tumbling, or more probably precession coupled with pronounced yawing, is well-known from the early days of the M-16’s development. I remember that a rifleman had little chance of hitting a man-sized target at 300 yards with early M16 rifles. The bullet design/twist rate combination had not been worked out correctly at that time.
With a right-hand twist, the precession spiral would be clockwise from the shooter’s perspective. I would also expect the spiral to enlarge as the pellet gets further from the muzzle.
Okay–so what does all this toffee-nosed drivel mean to real airgunners? It means that even if you correctly adjust your scope for trajectory, there’s still a big chance you won’t hit that half-inch kill-zone at 15 yards. Not because you’re too high or too low, but because you are too left or too right! If you’re throwing a spiral and your pellet isn’t centered on the line of sight at the range you expect it to be, you could miss.
What to do about spiraling pellets
Don’t shoot them! Find other pellets that don’t spiral, because they don’t all do it. If you can adjust the velocity, such as with a PCP, try that. My experience, though, is that if a pellet spirals from a certain airgun it tends to do it all the time, regardless of what you do.
Sometimes the optical axis of the scope is not aligned with the bore. This will give you similar results to the spiraling pellet, with some important exceptions. The first of these is the fact that the pellet will always be on one side of the centerline until it crosses over the line at some distance. Then it will remain on the other side. A spiraling pellet moves back and forth across the centerline.
When the scope isn’t in line with the bore, this happens. It may be very subtle and difficult to see and the slant can go either way — to the left like this or to the right.
The second exception that the misaligned scope gives is the pellets fly in a normal trajectory. Pellets that spiral do so up against gravity as they fly downrange. The center of the spiral drops in the usual way but as the spiral widens, these pellets sometimes actually appear to be rising! You have to keep in mind that these pellets are actually flying on their own, due to low air pressure on one side. Thus they seem to defy the laws of physics.
How to correct the misaligned scope
There are a couple of things to consider here. First — is the scope base on the rifle the thing that’s misaligned? Reader shootski talked about having to correct a firearm that was drilled and tapped for scope rings in the wrong place. If that is the problem, you should first consider whether it’s worth the time and effort to correct. If it is, spend the time and money to do it right.
Once the scope base is either fixed or ruled out your next concern are the rings you intend to install. Are they worth it? A $10 pair of rings from the discount store can give you many of the problems we have just discussed. I own many dozens of rings, but I only use the ones I trust.
Once you have the rings you intend using, remember what was said about swapping them end-for-end and even turning them around individually if they are 2-piece. When you have exhausted all the repositioning options, consider using a different set of rings. I know this flies in the face of shooting on the cheap but which would you rather do — save money or hit your target?
Setting up a rifle
You buy a new air rifle and there is joy in your castle! This new rifle will solve all your problems. It is infinitely accurate (whatever that means) and powerful enough to get the job done. Let’s say you stretched for this one and the new rifle cost you $280, delivered. But wait! You are not done. Figure another $100-150 for a decent scope — not a world-beater but also not one from the bargain barrel. Mounts will cost another $20-50, depending on the rifle and what you want to do. Your $280 investment just swelled to $400 to $480. That’s how much your new air rifle really costs! No wonder so many people swear by open sights!
Then, and only then, do you get to go through all the steps we have addressed in these five reports. Oh, and someone says, “That’s why I always buy the scope that comes bundled with the rifle I’m buying.” And do you also take delivery of that new $45,000 ATV with the tires they put on at the factory? Now, I know that remark is going to start a firestorm of controversy, or at least it should. Unless you guys don’t know tires!
If there is a lot of discussion about the tires, just substitute bundled scopes and scope mounts for tires and you will understand what I am telling you. Are all bundle deals bad?
BB did NOT say all bundled scopes are bad!
No, all scopes and mounts that come bundled with rifles are not bad. Let me give an example. The Sig ASP20 that’s bundled with the Whiskey 3 scope is a great deal! Yes, it does cost a lot of money, but it is a perfect example of you get what you pay for. It’s not a bundle where they are getting rid of scopes they can’t sell.
There are other good bundled scope deals. Look to the dealers who bundle — they seldom have warehouses of scopes to get rid of, and your loyalty means a lot more to them than it does to a manufacturer who looks to three or four major outlet chains as their primary customers.
This is one you need to experience to appreciate. Some scopes resist being adjusted until they are jarred once or twice. These tend to be the less expensive scopes and they usually wind up on spring-piston rifles that have all the jarring they need. This failure to move to the new adjustment is called stiction. I’m not qualified to explain what it is, but I think it is a combination of static electricity and a weaker erector return spring — or a spring that is fully relaxed.
The solution to stiction is to bump the scope with the heel of your hand after every adjustment. Either do that or fire the rifle twice before firing for record. I wish I could tell you what to watch out for, but all I know is when a scope doesn’t have stiction it becomes one of my favorites!
Sighting-in for one distance
This is not about any special techniques or tricks. It’s just an eye-opener that we all need to be aware of. When you sight in a scope for one distance, like 100 yards, and you leave it there you solve a large portion of all the scope problems there are. Canting is still an issue but all the stuff I’ve discussed today is moot.
It’s only when you want to use your scope at different distances that these things arise. And there is something you can do about it. Use the lowest power magnification you can get away with. I don’t expect you to shoot squirrels at 100 yards with a 2-power scope, but 6 or 8 power is much better than 32 power. Why? Because it takes your focus off minutia. It does what open sights do, only it also helps those whose eyes aren’t up to the task.
Field target competitors are an exception to this, so they need to set their scopes to work well between 10 and 50 meters. They could care less what happens at 60 meters, where a hunter has to care. The field target competitor has a harder job because of the range in which his scope must work, but at least there are boundaries.
I have addressed several concerns you readers have raised, plus a couple of my own. I will watch the comments to this report to see if any more in this series are required.