Scopes - Part 2
Scope mounts - How well do they need to fit?
by B.B. Pelletier
Chapter 1, Part 1, Selecting a scope
This is an ongoing tutorial that I hope to turn into a book on scoping airguns. Chapter 1, Part 1 was all the way back in November, and I bet you thought I'd forgotten about this project. I haven't, but other things kept cropping up. There will be more to Chapter 1, Selecting a scope, but today I want to begin Chapter 2 on Scope mounts.
This subject is daunting to those who haven't scoped an airgun yet and emotionally charged for many who have. I make no claim to be an expert in this field, but I bet I've made as many mistakes as anyone who ever scoped a gun. Through the benefit of those mistakes, I can discuss scoping with you. Today, I want to talk about how the scope fits the rifle - specifically, the width between the dovetails.
Back in 1998, Dan Bechtel, the founder and then-owner of B-Square, enlisted my help in measuring the width of airgun dovetails. He started this project because B-Square was encountering wide variations in the width of what the industry called an "11mm dovetail." I want to make it clear that I am only talking about straight airgun dovetails, not Weaver or Picatinny dovetails.
Bechtel told me we needed a standardized method of measuring dovetails, because how you measure them determines their width. You cannot simply measure from the sharp point on one side to the sharp point on the other side, because that will tell you nothing about the depth of the dovetail grooves. The depth and the shape of the grooves matters a lot to the fit of the scope mount.
We settled on the method of laying a one millimeter-diameter pin into each dovetail and measuring across from the outside of one pin to the other. I hope the drawing I provided makes this clear to you. Since the one millimeter pin would only go into the grooves so far, we were always measuring the same way, regardless of the angle that was cut into the dovetail.
For more than 6 months, I measured as many airgun dovetails as I could lay my hands on. B-Square technicians did the same. From this data, B-Square compiled a list of scope groove dimensions for many models of air rifles. They learned, for instance, that a "standard" 11mm dovetail can measure less than 9.5 mm or greater than 13.5 mm...and anywhere in between! Then there are rifles whose bases are different, such as the Webley Patriot/Beeman Kodiak and the FWB 121/124/127, which have cross-slots to accept half-round pins as a scope stop system. From that data, they started building their scope mounts to fit specialized situations. They also tried to make their common scope mounts fit as many air rifles as possible, and therein lies today's lesson. How they accomplished that task, now that you know what they were up against, determines how well their scope mounts fit various rifles. Allow me to illustrate.
Original AA mount
This mount is made to fit a single air rifle - the Webley Patriot, which is also the Beeman Kodiak. Its clamp is the same one found on all original B-Square adjustable mounts. Notice at the top of the separate clamp, the point isn't sharp but rounded. It's a ball end that will pivot in the specially prepared groove into which it fits. Therefore, the bottom of the clamp can extend out farther or in tighter and still fit correctly. However, the gap between the clamp and the body of the mount will not be the same size at the top and at the bottom. This difference disturbs some airgunners and has convinced a lot of them that certain mounts don't fit certain air rifles correctly. The fit seen here is nearly perfect, but what you see here is not often the case. It only fits this well because this mount was made specifically to fit the Patriot it's mounted on.
B-Square started sourcing their adjustable mounts from China and the original specification did not make it into the contract. The Chinese manufacturer uses more conventional extrusions instead of the ball-and-socket arrangement B-Square designed. Their mount still fits and works fine, but the clamp is now stuck way out on an angle and disturbs many shooters. In fact, the scope stop pins are what aligns the scope mount and the gun, so even though it looks like this, the mount still works.
When other manufacturers start turning out scope mounts, they may never have given them the thought B-Square did initially. As long as they clamp and hold, they're sold. The truth is that if they hold solidly, they're okay. But, they may not look as good as some other mounts. The scope, which is a round tube, can be set up level, even when the rings that hold it don't look right.
The bottom line
Brownells sells special centers for the precise alignment of scope rings. Many shooters will have their scope rings lapped by a special tool before mounting a scope. Do guns that have had these measures perform any better in the field? Sometimes they do, but often they don't. A well-mounted scope has more to do with the rifle than with the scope mounts. That doesn't stop some shooters from wanting things to look right.
Beeman used to sell the SS2 scope with different sets of separator pins to keep the clamp leg parallel to the main mount body. The scope mount was built into the scope, and Beeman understood how shooters worry about the look of their rifle.
What do you do?
If the look of the scope mount bothers you, then get it fixed, because things like that will play on your mind and erode your confidence in the rifle. As you are doing so, however, don't think for a moment that the appearance really matters. The clamp can be splayed way out to the side, but the gun will still shoot fine. Never underestimate the aesthetics of the rifle. For some shooters, they're everything.