- All about scopes. Part 2. (February 2005)
All about scopes. Part 2. (February 2005)
By Tom Gaylord Covered in this article:
exclusively for PyramydAir.com. © Copyright 2005 All Rights Reserved
Naming the parts
Let's mount them up
In this article we name the parts of scope mounting systems, present standards, and mount a scope, following simple step-by step instructions.
Many shooters scope their air rifles. In fact, a scope sight is the number one accessory an airgunner purchases. But people often feel that mounting that scope on their rifle is a technical challenge beyond their capabilities, when, in fact, it is one of the easiest things there is.
Much of the confusion comes from firearms. You can't shoot a firearm indoors at any great distance, so for decades gunsmiths have been mounting and aligning scopes using an optical device called a collimator, which helps align the intersection of the bore axis and the sight axis at some planned range. Scales on the collimator allow gunsmiths to adjust the scope so the rifle has a high probability of being somewhere on a paper target at the selected range, which is often 100 yards for centerfire rifles and 25 to 50 yards for rimfires. Remember - the best the collimator can do is get you on paper at those distances - you have to finish the job by adjusting the scope while shooting the gun.
With an air rifle, you can sight-in starting at 10 feet and finish at 10 yards, if you want to. I'll show you how in another article. There is no need for a collimator because you are so close to the target that, even if the scope needs a huge amount of adjustment, you will still be hitting the target paper. Before we start mounting, let's clear up some confusion about the naming of scope mounts. What are mounts, rings and bases; and how do they differ?
The term "mounts" includes both scope bases and rings. On firearms the distinction may be important, but since most adult airguns are designed to mount scopes, the bases are already installed. On less expensive Crosman, Benjamin/Sheridan and Daisy guns, a separate mount base is often required. It is attached to the gun first, then the scope rings attach to it. But for most adult air rifles, the base is already on the gun when you buy it.
The standard scope base for airguns is a set of two parallel 11mm dovetail grooves. If the gun is a recoiling spring gun, there should also be some kind of scope stop to interface with the rings. This "standard" is very loose, which is why there are so many proprietary scope rings manufactured for specific brands and even certain models. When you buy scope rings, have the salesperson check to make sure that what you are buying is intended for your airgun.
On this TX 200 spring rifle from Air Arms, there are two parallel dovetail grooves with three scope stop holes between them. Select one of these three holes for the scope stop pin on the rear mount (or if you use a one-piece mount, put the pin at the rear) to engage.
One final word on Weaver and Picatinny bases. These are firearms bases that perform the same function as an airgun scope stop. They keep the scope rings from moving on the base during recoil. Shooters coming from the firearms side of the house are very familiar with these bases, but no airgun is manufactured with them today. B-Square does make an 11mm to Weaver adapter base that allows the use of Weaver-base rings.
Rings are what hold the scope in place. For airguns, scope rings come with their own bases that are designed to attach to the scope base found on the rifle (or attached as an option in the case of guns like the less expensive guns mentioned above). I have selected non-adjustable rings for this article. They are easier to explain than adjustables. We may do a special article on B-Square AA adjustable rings in the future, but this time we'll look at non-adjustable mounts, which are by far the most popular and commonly used. I selected two-piece rings, because they are more flexible to use. One-piece rings are installed the same way, but they allow fewer mounting options because wherever the one ring goes, the other is always attached.
I have selected the most difficult type of rifle to scope, a recoiling spring-piston air rifle, to demonstrate all the details of scope mounting. Precharged and other pneumatics plus CO2 guns are easier, as are recoilless spring rifles. I will use a TX 200, which is not a hard spring rifle to scope, but I will cover the details the same as if we were scoping a real kicker.
Two-piece scope rings give more flexibility when positioning on the airgun. They are equally strong, rigid and true as one-piece rings.
One-piece scope rings have the same features as two-piece rings, but they are heavier. Some shooters prefer them to two-piece rings.
One thing should always be in your mind. Will my scope have enough clearance when mounted on the rifle with the rings I select? Look at the photo of the scope mounted to the TX 200 to see what I mean. If the objective lens were much larger, this scope would require higher rings to fit this rifle. Step 1. Attach the scope ring(s) to the rifle. The TX 200 has three vertical stop pin holes, as seen in the photo. Put the stop pin of the rear scope ring in the one that seems best for your situation. For guns that don't have holes, the pin may rest against the mount base that's permanently attached to the rifle. The pin's purpose is to stop rearward movement of the scope rings and therefore, of the scope itself.
Airguns that don't recoil (like precharged guns) don't need a scope stop. If you are mounting to one of these, you need to remove the stop pin from the base of the ring.
Remove the top caps of the ring(s) as shown in the photo before installing them on the rifle. The reason for this will be made clear in the next step. Snug the rings so they don't move, but don't tighten them all the way yet.
The rings are mounted on the rifle minus their top caps. The scope is laid in them for positioning.
Step 2. Position the scope. Lay the scope on the open rings and position the eyepiece by sliding the scope back and forth. You may have to move one or both rings to get this right.
Position the rings so the scope's eyepiece will be the correct distance from your shooting eye when the gun is held naturally. This is usually between two and three inches from the eyepiece lens, but it is the spot at which the image in the scope appears as full and bright as it gets. To see what this looks like, move your head back and forth along the stock, as you look through the scope with both eyes open. Then, position your head on the cheekpiece where you want it to be and move the scope back and forth until the image appears bright and full.
Now, put the top caps back on each ring without moving the scope forward or backward. Tighten them until the scope is held secure but can still be rotated with your hand. That isn't very tight!
Step 3. Align the scope's vertical reticle. Align the vertical reticle with both eyes open and the gun held naturally to your shoulder. Rotate the scope until the vertical reticle seems to bisect the gun perfectly. Now you can tighten the base of the rings securely to the gun.
Once the position of the scope is determined, the rings are tightened to the gun and the top caps are installed. Center the vertical reticle before tightening the caps.
Step 4. Tighten the top caps to hold the scope. This is a step where care should be taken. There is no need to over-tighten the ring caps to hold the scope in place, but most people overdo this part.
Tighten each screw partially, then move to the next one and go around the pattern of screws many times, rather than tightening each screw all the way on the first try. You will put even tension on the caps and be less likely to dent the scope tube this way.
If there are two screws on the side of the ring, tighten only one, then tighten the one on the opposite corner of the other side of the cap (see graphic below). Leave the other two screws for the moment and tighten two screws on the other ring next. Then come back to mount one and tighten the two screws you left loose. Then back to the other ring and keep rotating until the scope is secure. It takes less tightening that most people think, so err on the side of too loose, rather than too tight.
Keep going around the pattern, tightening very little each time. I hold on to the small end of the Allen wrench to keep from over-tightening.
Some folks try to get the same amount of space between the caps on either side of the mounts, but I don't worry about it very much. Once the screws are tight the job is finished. Now the scope can be sighted-in.