by Tom Gaylord
Writing as B.B. Pelletier

This report covers:

  • The problems
  • Problem 1 — All rifles are droopers!
  • Problem 2 — horizontal alignment
  • Problem 3 — scope eyepiece is in the wrong place
  • What is the solution?
  • Clearance
  • Summary

Today’s report was partly inspired by reader Decksniper, who asked this about the Seneca Aspen rifle:

“I am interested in the shim you used to mount the Bugbuster on the too narrow dovetail. A closeup picture would be helpful.”

I told him I would photograph the shim in the next part about the Aspen, and I will, but this morning (yesterday for you) I was faced with scoping another rifle — the Diana Stormrider Generation II PCP, and it suddenly dawned on me that scoping airguns is one of the biggest challenges I face in writing this blog. As I pondered that it occurred to me that scoping guns is a challenge for all of us. Some may not have realized what a challenge it is because they have become adept in avoiding the problem altogether, but a challenge it is.

Heck — it’s a challenge to scope a firearm, too. That’s why people pay gun shops to boresight their rifles for them. When they get out to the range I see that they haven’t got the foggiest notion of what to do next. That always happens on the 100-yard firing line, where they will staple a cardboard pie plate to the backer board and sit at the shooting bench for an hour in frustration, wondering where their bullets are going. At least airgunners can start out at a closer distance, so they have a little better chance of connecting with paper!

By the way, these firearm shooters often show up at the range with a fresh box of 20 cartridges, expecting to get zeroed in 4-5 shots. Ha!

The problems

Today I want to talk about the problems of scoping an airgun for the first time and tell you some of the things I do to address them.

Problem 1 — All rifles are droopers!

My first assumption is that all rifles are droopers. Their barrels point down in relation to the scope base on their receivers, which means they will invariably shoot low. Is that true all the time? No, it’s not. But the number of guns (airguns and firearms) that DON’T droop is minuscule compared to the ones that do — at least in my experience. People sometimes ask me what if they correct a gun for droop when it has none. Is that a problem?

Most of the time it’s not. You just end up with more vertical adjustment. There is no problem adjusting the scope on a normal rifle down below the midpoint of the elevation range. You can take it all the way down to where the adjustments stop and the scope will perform as it should. Unless the barrel is bent up and the rifle shoots too high, this will not be a problem.

It’s when you adjust above the midpoint of the vertical range that problems start to occur. At some point in the upper range of vertical adjustment the erector tube inside the scope where the reticle lives will loose all spring tension and start to “float.” At that point the reticle will start moving with the vibration of each shot. You will see that as scope shift. You won’t be able to hold a solid aim point.

I’m not going to discuss all the methods of correcting this problem, but I will name them.

1. Shim the scope.
2. Use an adjustable scope mount or base.
3. Use rings or a scope base that has droop compensation built in.

Problem 2 — horizontal alignment

I’m talking left and right now. You sight in at 10 feet and your pellet strikes the paper 6 inches to the right of your aim point. If you back up to 10 meters without correcting it the next pellet is going into the wall!

When it’s bad like this you can always see the cause. Hold the rifle so you look down on the scope and compare its line to the line of the barrel. It will be noticeably off or angled. The reasons for that are varied.

1. The scope rings are not correctly mounted on the scope base. Look closely at the pointed jaws of the scope rings and make sure that are in the grooves where they are supposed to be. If you have two piece rings, one will often be mounted correctly and the other one will be out of the grooves on one or both sides.

2. You are using cheap rings that are not bored straight. This doesn’t happen with quality rings, but with cheaper rings it’s common. The angle will be harder to see when this is the problem, which is why bargain scope rings are never a bargain. With two piece rings you can sometimes fix the problem by turning one or both rings around, or by swapping them, front and rear — or a combination of both things.

3. The grooves on the rifle are not cut straight with relation to the barrel. This is not common.

4. The barrel is offset. This happens on PCPs that have free-floating barrels. There is usually a barrel hanger with two or thee small screws that can be loosened so the barrel can be pressed back into alignment with the scope and receiver.

Problem 3 — scope eyepiece is in the wrong place

The eyepiece is positioned incorrectly so your eye does not see the full image in the scope. This is very common with compact scopes and with one piece rings. Both force you to mount the scope someplace on the rifle that may not correspond with where you need it to be. The solution is not simple, but here it is.

1. Take the scope you intend using and see how far from your eye the eyepiece needs to be for the image to be full. Usually there will be a short range of distance. Once you find it, find a scope mount that allows you to position the scope there.

Woah! That’s a lot of you in the solution, isn’t it? There must be an easier way.

Many new people ask the salesperson to recommend a scope and mount that will be right for the rifle they are buying. There’s just one huge problem with that. The shooter is also a factor in the scope mounting equation and, unless that is taken into account, they are just guessing. Some things to consider:

1. How long is your neck?
2. How broad are your shoulders?
3. At what angle do you hold a rifle, relative to your body and the intended target?
4. How consistent is your cheek weld?
5. What is the shape of your face?

Selecting a scope and mounts for a rifle without seeing both beforehand is like buying a car, sight unseen. No, it’s worse than that, because cars are purposely made for a broad range of drivers. Buying a scope and mounts without seeing both together with the rifle is like getting glasses without having an eye examination.

What is the solution?

I have just told you that it is nearly impossible to get a scope and mount without seeing them in person. Is there any hope? Yes, there is. Here are some things that will help you a lot.

1. Use two piece rings. These give you a broader degree of latitude as to where the scope eyepiece can be.

2. Get a scope with a long eye relief. Eye relief is a measure of how far your eye needs to be from the eyepiece to see the whole image in the scope. Some powerful scopes have a very short eye relief and demand that your eye be in the exact spot or the image will appear black. This isn’t always bad, because it helps you position your eye in the same place evey time, which minimizes parallax errors. But it’s not as flexible.

Lower powered scopes usually have a very long eye relief and are very easy to use. The down side is they have a larger parallax error. That may not matter if you don’t care about the last bit of accuracy.

Clearance

Getting the scope to clear the parts of a rifle is another concern. This is where a salesperson should be able to help. There are a couple things to watch.

1. Does the objective bell clear the rear sight or barrel or barrel band? The rear sight is the biggest issue. A scope with a large objective bell that’s mounted in lower rings may not clear the rear sight and even the barrel.

2. Does the objective bell clear the breech of a breakbarrel when the rifle is cocked? Long scopes are at issue here and this is something that is difficult to determine without having both the scope and gun in hand. Sometimes the scope can be moved back a little, if the eye relief will permit it.

Summary

Those are the main things that I face every time I scope an airgun. Are there others? Sure. Things like:

1. Is the scope clear enough and powerful enough for the kind of shooting intended?
2. Are the rings the right diameter for the scope tube?
3. Is the base of the rings compatible with the scope base on the rifle?
4. Are the reticle lines appropriate for the kind of shooting I intend doing?
5. Do my scope mounts have the right scope stop for the gun I’m mounting them on?

Scoping an air rifle is a challenge for me because I test so many different air rifles. It’s a challenge for you because you don’t have that many scopes and mounts to pick and choose from.

All of us want a well-mounted scope. It’s so much easier to shoot when the scope is mounted correctly. I have had to learn to adapt to guns whose scopes may be less than optimum. I hope you don’t have to do the same.