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Education / Training Scope mount basics – part two

Scope mount basics – part two

by B.B. Pelletier

Can you use 3/8″ dovetail rings on an airgun?
You can but you shouldn’t. Three-eighths dovetails are found on .22 rimfire rifles, and the mounts made for them are mostly very cheap. They won’t stand up to the abuse of a spring rifle. They’re flimsy no matter what gun they’re on.

These are the rings you find in discount stores, and they are there because they are so cheap. Buyers are looking for the absolute lowest price for an item, and they don’t know or care how well the rings will (or won’t) work when they try to use them.

Strictly speaking, 3/8″ is a little smaller than the 11mm dovetail found on airguns, so these cheap mounts will also be awkward on your gun. This is not a place to economize; buy good airgun mounts and you won’t be sorry.

One piece or two?
This is a choice you must make, and I’d like to make it easier for you. Airgun scope mounts come in both one-piece mounts and two-piece mounts. One-piece mounts are somewhat more convenient to attach to most airguns, but they don’t fit well on guns that have split dovetails or something blocking the dovetail, such as you’d find on the Webley Spectre.

One more thing about one-piece mounts – the rings are a fixed distance apart that cannot be changed. That can make attaching them to some compact scopes, such as the Leapers Bug Buster, impossible because the rings are too far apart.

One-inch rings or 30mm?
Most airgun scopes have a tube that measures one inch in diameter. These scopes need one-inch rings. Some of the extra-bright scopes, such as the Leapers mil-dot range-estimating scope, have a larger 30mm diameter scope tube. For these you need 30mm rings. Other than the ring size, the mounts are identical, but you absolutely cannot fit a 30mm scope into one-inch rings (or vice-versa).

Scope alignment problems
Your scope may not have enough adjustment to bring the group to the aim point. Usually, the group will be low and often to the left, as well. When this happens, you either have to shim the scope or use an adjustable scope mount.

Shimming means to put a shim or thin material under the rear scope base (if you have two-piece mounts) or between the scope and the bottom of the rear ring. This slants the scope downward and brings the group up to where it needs to be. Shim material can be thin plastic, photographic film and even metal shim stock purchased at a store for that purpose. Don’t add as much as the thickness of a business card, or you’ll risk bending the thin scope tube when the rings are tightened.

If you’re shooting left or right, try swapping the rings front and back and even turning them around (if they are two-piece). This can sometimes help the elevation problem as well.

You may need adjustable mounts
Adjustable scope rings move up and down and left and right to perfectly align the scope without resorting to the scope adjustment knobs. They are more difficult and time-consuming to install, but you’ll never run out of scope adjustments with a set of them. And, they keep your scope adjustments closer to the center of the range, where the scope performs better. Read about that in the March 24 post “Another cause of scope shift: over-adjusted scope knobs.”

Mounting a scope can be challenging, but it’s not beyond any of you. Selecting good mounts is a great way to begin.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

12 thoughts on “Scope mount basics – part two”


  2. Dave,

    I’m so glad to hear that you may have solved your scope mount problem! One thing I failed to mention before is that B-Square attempts to fit so many different widths of dovetails that they round the corners of their mount base dovetails more than most companies. As a result, they can slip out of the dovetails on a rifle like the Tomahawk under recoil. I had forgotten that until a few days ago.

    I have always believed that 10.5 Premiers are best for PCPs and 7.9 are best for springers. I bet JSB Exacts are the best in your rifle. I really like that pellet!

    Thank you for getting back to me with the outcome of your problem. I hope you enjoy your Tomahawk.


  3. Joshua,

    I don’t know what criteria you are using to determine “best” for an air pistol. Do you want accuracy, power or repeating action? If you say, “Yes, I want all of that.” then I think the S&W 586-6 is your best bet. If a single shot is okay, then I like the Benjamin HB 17 or HB 22 (or the EBs, if you like CO2). If you want a classic air pistol, the Webley Hurricane or Tempest is the way to go. And if accuracy is at the top of your list, I’d try a Beeman P3. The best DEAL on an air pistol is the Marksman 2004. It’s a Chinese copy of the Beeman P3 and I understand it’s pretty nice.

    For the RWS 24 in .177 I would try RWS Hobbies and Crosman Premiers in 7.9 grains. In .22 I’d try Hobbies and RWS Superpoints. Also try Daisy Max Precision Pointed pellets.


  4. i have a gamo shadow 1000 that eats scope mounts, i have gone through three pair all ready, i have gone through 2 pair of b square and one pair of air force, the mounts just keep jumping off the dove tail at the end, and ruining the clamps, is this common with springers or am i doing somthing wrong, i have tried a mount stop but that did the same thing
    on the brighter side of it i have become a better shot with open sights lol

  5. My gamo shadow 1000 came with a scope stop but after about 20 shots the scope stop pops off from the scope pushing on it. Then after a few more shots the scope is no longer accurate and falls off also.

  6. Gamo Shadow,

    I have never hear of the Gamo scope stop falling off like yours did, but I do know that the screws on spring guns loosen all the time from vibration. I’m guessing that’s what happened to you.

    Dit you try to reattach the stop?


  7. I recently purchased a Gamo 1000 Shadow and am astounded to hear of this scope mounting problem. I purchased a Gamo 4×32 scope w/rings at the same time and carefully mounted them and rechecked all screw torques periodically (not over tighten) and surprisingly found None of Any of the entire gun assembly to be even the slightest bit loose as Springer guns are prone to do. Try blue Locktite if needeed, clean threads first and shake bottle first. In other words : READ ALL INSTRUCTIONS CAREFULLY BEFORE YOU DO ANYTHING!

  8. I too just bought a Gamo S 1000 and was wondering how you guys got around the front sight with a scope. Do you guys use high scope mounts or remove the front sight? I have a Leapers 3×9-40 scope and medium mounts and the front of the scope barely is above the stock of the gun. Any suggestions?

  9. I just got my Gamo Shodow 1000 the other day, went to put on my scope and found out the groves for the mounts just are not cut right. The left side was fine but the right side is cut at almost at a 90, so after I put it on I can just pull it right off? I dont want to take it back because there are no more of them and very hard to find now! I might have to have a friend machine a small grove into it for the mount to have something to hold on to. Other then that I love this gun!


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