Posts Tagged ‘BKL adjustable scope mount’
by Tom Gaylord, a.k.a. B.B. Pelletier
This is an ongoing series about scope questions and issues. Blog reader David Enoch asked for it originally, but many other readers have jumped in since it began. Today, I’ll talk about adjustable scope mounts.
First things first
Why do we need adjustable scope mounts? Aren’t the scopes, themselves, supposed to adjust? Yes, they are, but 2 things quickly become a problem. First, the scopes don’t adjust as far as we need them to; and second, when a scope adjusts toward its upper and right limits, it loses its precision. I will address the second problem because it’s really the principal one.
When we look at a scope, we see that it has a range of adjustability and assume that it’ll work as it should throughout this range. But that’s not the case. Inside each modern scope there is a smaller tube called the erector tube. The erector tube often contains the reticle; and as the tube moves up, down, left and right, so does the reticle. So, moving the erector tube is what moves the reticle.
There is a spring or springs that press against the erector tube, making it press against the adjustment knobs, in turn. That spring has a range of movement it goes through as the tube moves. When the tube is up high or far to the right, then a spring or springs that press it against the adjustment knob or knobs are relaxed and can allow the erector tube to move when the gun vibrates, such as with a shot. This is one of the chief causes for “scope shift.” You fire the gun, and the erector tube moves slightly, taking the reticle along with it, of course. On the next shot, the scope will be aiming at a slightly different place. It’ll appear that your scope is wildly throwing the shots around.
This elevation knob is adjusted up to its maximum limit. I recommend not adjusting it higher than the number 3 line on a scope like this to avoid scope shift.
I tell folks that a good rule of thumb is to not adjust their scopes above the 3/4 mark on the elevation knob or past the 3/4 mark on the right windage adjustment. Some scopes can adjust farther than this without a problem; but the closer you stay toward the middle of the range, the better. If your scope doesn’t have knobs like these, you may have to count the actual clicks of adjustment to know where you are.
Is adjusting the scope in the opposite direction (i.e., down or to the left) a problem? No, it isn’t. You can adjust all the way until the adjustments run out in the down and left directions. It doesn’t hurt the scope, nor does it affect accuracy.
So, the scope that you thought had a huge adjustment range turns out not to have as much as you believed. Yet, your airgun (or firearm) needs more adjustment than you have. How do you compensate for the adjustment you no longer have but may need? With a scope mount that adjusts, of course.
Adjustable scope mounts
The purpose of an adjustable scope mount is to align the axis of the scope in a direction different than the scope base on the gun dictates. If all scope bases were aligned with the axis of the barrel, there wouldn’t be a problem, but they aren’t. Adjustable scope mounts can compensate for this, leaving the scope’s internal adjustments to serve the ballistic requirements of the gun in question.
Up and down, left and right
A barrel can point off from a gun’s scope base in any direction, but the most common direction is down. The barrel “looks” down, in relation to where the scope tries to look. The other 3 directions are also possible, with left being the second most common. After that, the other 2 directions happen pretty infrequently.
So, if you’re going to need extra adjustments, it will most likely be extra “up” that you need, followed by extra “right.” Adjustable scope mounts have to provide extra scope movement in all directions, with up and right being needed most often.
Scope tube integrity
The scope tube is a hollow, rigid tube that must maintain its integrity to keep the lenses in alignment. If the tube were to bend, it could seriously damage or even break the scope. Adjustable scope mounts must either move the scope as a whole without putting any stress on the tube, something that only a 1-piece mount can do; or they must adjust in such a way that when the rear mount moves, the front mount can relieve the stress on the scope tube. Only the B-Square AA adjustable scope mounts were able to do that; and when B-Square sold the company several years ago, the new owner moved the manufacture of the AA adjustable mount to China, where the quality control was soon lost. You cannot buy new AA adjustable scope mounts any more.
When the rear mount is raised above the front mount, if the front mount doesn’t move to compensate, the scope tube will be strained. These B-Square 2-piece AA adjustable mounts have rings that pivot forward to allow the scope tube to remain straight.
Sports Match has 2-piece adjustable mounts on the market; but as far as I can see, they make no provisions for relieving the stress on the scope tube when the rings are adjusted separately for elevation. I guess I need to test them to learn their operational parameters. I don’t see how they can avoid stressing the scope tube when the front and rear mount are at different heights, but I’m willing to hold my opinion until I’ve examined them.
I’ve tested several 1-piece adjustable scope mounts and found all of them to work well in this regard. Most recently, I tested the BKL adjustable mount and found that it moved well in both directions.
What about precision?
To date, no one has made an adjustable scope mount that adjusts with precision for a modern scope. Such mounts do exist for vintage scopes that have no erector tubes because the entire scope has to be moved by the mount. I have shown you this kind of adjustable scope mount a couple times.
This Unertl scope ring adjusts to move the entire scope. It has the same precision as the adjustments on a modern scope.
Slippage is common with adjustable scope mounts
The most common problem is the adjustable scope mount that does not hold its position. That’s why the Chinese-made B-Square adjustable mounts failed. Their screw holes had sloppy threads that tore out under stress, and the mounts couldn’t hold in position. So, whatever adjustable mount you get, it must hold its position once it’s been adjusted, or it won’t work.
And slippage happens soonest on spring guns because of their recoil and vibration. Ironically, spring guns are the very ones that need the adjustable mounts most often. There’s nothing that can be done about this, but you must understand that you don’t want a scope mount that can’t hold its position.
Firearms shooters need adjustable scope mounts more today than ever before. I think that’s because modern guns are being assembled faster and with less precision than they were in the past. The thing is that firearms shooters are not as aware of scope problems as airgunners, so they tend to have more of them; and when they do, the problems are harder for them to resolve. I’ve tried to help people who I knew were having some common problems such as adjusting too high in the scope’s range, but they just looked at me like I was crazy. Surely, no scope manufacturer would field a scope whose adjustments were not 100 percent useable?
That’s all I have for you today. How about telling me your other unresolved scope issues?
by B.B. Pelletier
It’s been half a year since I did Part 1 of this report. I always meant to do today’s test, but other things seemed to crop up every time I was ready. I did make an excursion in another direction to test BSA’s 2×20 pistol scope using another mount on the Beeman P1 air pistol. Such is the tangled life of the airgun blogger!
Today’s report takes me into fresh territory with my Slavia 631 breakbarrel rifle. I had earmarked it as a testbed rifle for testing the accuracy of lead-free pellets a long time ago, but the lack of a scope mount caused me to substitute the Whiscombe rifle at the last minute. You see, the Slavia air rifles all share a common problem when it comes to mounting scopes. They have dovetails that are among the very widest on the market. Most 11mm scope mounts will not expand wide enough to fit the 14mm dovetails (they are still called 11mm, which creates a world of confusion among buyers who try to scope their rifles) that are standard on all Slavia breakbarrels. Even for me — with a drawerful of specialized airgun mounts and prototypes — the Slavia remained a gun I could not scope until this new BKL mount hit the market.
Those dovetail grooves may be called 11mm, but they’re really 14mm apart. And that makes a huge difference. Almost no scope mounts will open that wide. Those three scalloped notches are for a specific type of scope stop that no longer exists in the U.S.
I’ve owned this 631 since back in the 1990s when I was still writing The Airgun Letter. I got it from Compasseco (now owned by Pyramyd Air) for a test and liked it so much I decided to keep it. Over the years, I’ve used it for other tests, such as testing the accuracy and penetration of round lead balls; but these tests were done with open sights. Today, I get to discover for the first time how the rifle shoots when a scope is mounted.
The BKL adjustable mount is a one-piece mount that just fits the length of the scope grooves on the 631. There isn’t a millimeter to spare on either end. As for the width, the fit is much easier, though I did have to spread the clamping rails to get it on the gun. For those who are unfamiliar with BKL mounts, they hold onto the airgun by clamping pressure, alone — there are no mechanical scope stops on any BKL mount. It’s often necessary to spread the mount base a little to get it onto the dovetails of the rifle. BKL has designed an ingenious way of doing this with the base screws applying reverse pressure to spread the base “jaws” just the right amount. It’s easy to do and takes only a minute or two extra. Once the mount is on the gun and the base screws are tightened, you have a scope mount that’s not going to move under recoil, no matter how severe.
The second great thing about this new mount is that the rear scope ring elevates to compensate for barrel droop. Newer readers may wonder what droop is, so allow me to explain
The BKL is mounted on my Slavia 631 rifle. The mount is silver because it’s an unfinished preproduction model, not because it’s finished that way.
Breakbarrel springers are notorious for having barrels that are angled downward from the sight plane. Because the manufacturers mount both the front and rear sight on the barrel, they remain in a fixed relationship that masks the droop or downward slant of the barrel. When you install a scope, it goes on the spring tube and the barrel droop becomes painfully obvious. You adjust the scope up as far as it will go to bring the strike of the round back up to the intersection of the crosshairs. Sometimes, you just barely get there, but other times you can’t even get that high before running out of adjustment. Either way, when a scope is adjusted all the way up as high as it will go, the internal springs relax and the point of aim starts moving all over the place. New shooters blame this on scope shift, but it’s really a different problem that’s completely correctable
You want to mount the scope in such a way that its vertical adjustment is about in the middle of the range or even closer to the low end. That’s where the droop-compensation scope mount, or “drooper” as it’s called, comes into play. With a droop-compensation scope mount you can slant the scope downward so it follows the line of the bore more closely.
And this new BKL is a drooper mount! But until I tried to sight in my Slavia 631, I had no way of knowing that it’s a breakbarrel with a droop problem. Once I confirmed that it is, I adjusted the rear of the BKL mount upward and got the scope dead-on at 25 yards! It took only one adjustment, and I had the scope back into the middle of its adjustment range again. Now, it was time to see how this rifle shot.
This is going to be a longer report, so I’m cutting to the chase right away. When I started shooting the 631 at 25 yards, I discovered that this rifle is twitchy. What does that mean? Well, if a breakbarrel is very powerful, it’s usually extremely difficult to hold for accuracy. It wants to spray its pellets all over the place — that’s what I call twitchy.
But lower-powered breakbarrel springers like this 631 aren’t usually twitchy. Usually, they lob all their shots to the same place. They’re also very tolerant of different types of pellets. But my Slavia 631 is none of those things. It’s twitchy. Allow me to show you what I mean. The first group I tried to shoot was with the Air Arms Falcon pellet.
This first target shot with Falcon pellets revealed a lot about the gun. Do you see that two pellets are close together in each of the three groups, but the point of impact moves? That’s due to very small changes in the hold. Four of the 10 pellets missed the target altogether!
The first group I attempted told me this rifle is twitchy. But sometimes that’s only with a couple pellets, so I pressed on.
Next, I tried shooting RWS Hobby pellets. They did better and were less twitchy but were not really that good.
Ten Hobbys went into a real group at 25 yards. It looks like only 6 shots landed because several went through the same holes. This is a better group, measuring 0.73 inches between centers, but it’s still not great.
I had to use every bit of technique, short of a scope level, to get that group. The differing points of impact were obviously the result of very subtle changes in the hold. This was obvious to me as I shot, because I was able to feel where the pellets wanted to go. But in spite of that, I did my best to shoot the tightest group I could.
I tried Crosman Premier lites next, but they were all over the place. Then, I tried the JSB Exact RS pellet that often proves best in rifles of this power level. This time, though, they were too hold-sensitive to do well.
Finally, I tried the BSA Wolverine pellet that’s also a medium weight JSB but is subtly different from the others of the same weight (8.44 grains). Like the Hobbys, I got a group of 10; but like the others, it’s interesting for being more of a cluster of several smaller groups.
Ten BSA Wolverine pellets gave this group, which measures 0.75 inches across. There’s a cluster of 6 in one hole, then 4 others below. The fourth shot lies between the two that are stacked vertically.
The BKL adjustable scope mount works as advertised. It’s easy to install and to adjust. And it has jaws that are wide enough for the widest 11mm air rifle dovetails. Just don’t try to use it on a Weaver base, because it isn’t that wide, nor is it configured for the proprietary shape of a Weaver dovetail. This mount is one elegant solution for a drooper.
The Slavia 631 is a twitchy breakbarrel that shoots at a mild level of power. If I hadn’t done this test, I never would have guessed that from the muzzle velocity, alone. That made me think of another report I can write — and probably should: What to do with a twitchy breakbarrel. It would be a collection of the tricks and techniques I would use when I encounter a twitchy breakbarrel. In my role as an airgun tester, I see a lot of them over time, so I’ve built up a bag of techniques I employ to deal with them when one comes along.
The 631 is also a great potential testbed for an adjustable muzzle weight to be used for tuning the harmonics of a spring gun. I’ll look into that.
by B.B. Pelletier
Once again, it’s time for me to fasten ice skates to the bottom of a stepladder, then try to skate across bumpy ice while carrying a flask of nitroglycerin. Seriously, that is how it feels to trust in something that all your life you’ve avoided because you felt it was too imprecise. Pistols and scopes just don’t mix in B.B. Pelletier’s world. But, today’s Part 2 of the test of BSA’s 2×20 pistol scope. It’s mounted on my Beeman P1 pistol, and I’m using BKL’s new 556 riser blocks to clamp to the P1 dovetail. I selected a pair of nondescript Weaver rings to hold the scope. They’re matte silver, so they don’t even match the finish on the pistol and the scope, but they work perfectly. You could use Hawke Weaver rings and do very well.
Last time, I was at 10 meters and wondering whether I would put a round through the wall behind the target trap. This time, I backed up to 25 yards — three rooms away from the target and wondered what damage I would wreak upon our house. Normally, I shoot handguns at this distance on a range, so this was a first. Even when I’ve tested other air pistols at long range, I’ve always shot out the bedroom window, but now I was trusting myself to keep them all on the target paper 75 feet away. Spooky!
No noticeable parallax
One reader asked me about parallax, but I was too busy not shooting the walls in the first test to notice whether or not the crosshairs moved when you move your head.
They don’t. Instead the entire image goes black. So, if you can see the image, no amount of head movement will make the crosshairs move on the target. If the image goes black, you’re done, anyway. Time to reposition the gun.
Parallax, of course, is the apparent movement of the crosshairs against the target; if your head is not always in exactly the same place, you’ll aim at different places on the target. With a rifle, you have a stock into which you press your cheek; but with a pistol, there’s no similar cue, so this was a good question. It appears the scope manufacturers have figured it correctly. At least BSA Optics has.
I was genuinely afraid that the pellet would not hit the target from 25 yards. After the first shot, I trained binoculars on the target to see where the pellet had gone. Because I was still shooting Crosman Premier lite pellets, I could not see the small ragged hole even through the binoculars, so I walked down and checked the target. Surprise! Even though the crosshairs had been moving all around the bull, there was a neat hole cutting the nine ring at one o’clock.
The next nine pellets also hit the target paper and gave me a group that measures 2.92 inches. I’ll be the first to admit this groups does not look that good, but please take into account that it was shot by a handgun at 25 yards. If I did this well with a .45 ACP, I’d be smiling. Of course, the big holes left by the bullets would make the group seem proportionately smaller.
I wasn’t satisfied with that group — other than all shots hit the paper. I modified my hold by holding the butt of the gun just in front of the sandbag rest, where before the gun had been six inches in front of the bag.
Group two was only slightly smaller, at 2.675 inches. If you look at it, eight of the shots made a group measuring just 1.743 inches. That seems a lot better to me.
Next, I put the actual butt of the pistol on the bag and held it there. The crosshairs grew rock-steady in this hold, and I thought I was on to something. But group three measures 3.467 inches — the largest to this point, and the largest group of the day, as it turned out. Apparently pistols need the artillery hold in the same way rifles do.
For the final group, I reverted to the hold in which the butt of the gun was just in front of the bag but not touching it. I was getting tired by this time, but I still managed to shoot a 2.311-inch group to end the session.
Forty shots and all of them on the paper at 25 yards. I’d call that success.
The scope is actually easy to use once you learn to trust it. I wasn’t used to seeing how much my hands shake and the scope really brings that out, so be prepared if you decide to get a pistol scope. I also find it difficult to believe that there’s any magnification at all. To me, it just looks like I am peering though a very clear window at the target about 40 feet away
I’m not finished with this test, because I still have to try the pistol with other pellets. I spent extra time trying to discover a good hold, and so far I’m satisfied. I’ll continue to experiment. For now, I think I know the best way to hold the gun for good groups. It just seems like those dang crosshairs are jumping all over the place!
by B.B. Pelletier
Pyramyd Air has marked down their line of Falcon PCP rifles. Save up to $190 on some models. Check ‘em out. Now, on today’s blog.
It took a long time to get me to this point. As a handgun shooter I’ve always had great disdain for scoped pistols, because I couldn’t see what purpose they served. But, like many other things about which I have a strong opinion, I was in the minority. I finally broke down and took the plunge. Today, I’ll begin a report on BSA’s 2×20 pistol scope mounted on a Beeman P1 pistol. There’s more. To mount the scope, I had the use BKL’s 566 riser blocks that clamp to the P1′s 11mm dovetail rail and offer a Weaver base on top. Because this is a BKL product, we know that it isn’t going to move on the gun, and the Weaver base assures us that the scope rings are not going to move, either. That makes this a perfect scope-mounting solution for the P1, whose recoil has always presented a problem for scopes in the past.
Speaking of problems…
In fact, I was going to use the new BKL adjustable scope mount that I reported on back in July. There was only one problem with that. When I tried that mount on the P1, the recoil went in the wrong direction and the adjustable legs of the mount lifted out of their adjustment yoke. When I checked with BKL, I found that I’d gotten my wires crossed and they never intended that mount to be used on the P1. I’ll continue that report by selecting an appropriate air rifle on which to test the mount, and today I’ll start the report on the correct mount solution for the P1.
Installation of these two BKL risers on the P1 couldn’t be much easier. Remove the clamping screws so the front sight blade will clear and just slide the risers onto the rail. Then, install the screw and screw them in until the risers are tight. The P1 has a very wide dovetail of nearly 14mm, so these risers are machined especially for it and other guns of equal width.
I located the risers forward, close to the front sight because I knew I needed clearance for my hand to cock the pistol. And where they wound up was perfect. The scope does not intrude on my grip when cocking the pistol, which on a P1 means lifting the topstrap and rotating it forward.
Because the BKL risers have Weaver bases on top, I was able to select some low Weaver rings to complete the installation. The BKL risers give more than enough clearance for the BSA 2×20 scope, which doesn’t have a very large ocular bell. The cross keys in each of the rings mean they’re not going anywhere.
The moment of truth approaches
Because the scope installation went so fast, I was now ready to begin testing, and this is where I faced my greatest fear. I’ve tested thousands of airguns throughout the years, but most of them have been rifles; and of the pistols I’ve tested, none of them ever wore a scope. This was my very first time. I felt like a unicycle rider who had agreed to walk a tightrope over Niagara Falls. Sure, I had good balance, but this was entirely new.
I think I felt like a new airgunner approaching a breakbarrel for the first time. What would keep the people from pulling back on the curtain and exposing me to all of Oz, when it became apparent that I couldn’t shoot this scoped pistol? Heck — I knew so little about shooting scoped handguns that I wouldn’t even know whether it was the gun or me that was putting the pellets into the drywall behind the trap.
The only thing that kept me on track was the knowledge that hundreds of other people have done this before. Surely if the emperor was truly naked, one of them would have spoken up by now? Then, the thought of present-day politics flooded my mind with doubt again.
Riding this turbulent sea of doubt, I addressed the target from 10 feet and let the first round fly. Wonder of wonders, the pellet went through the target paper! Not exactly where I’d aimed, of course, but close enough that I knew the danger of shooting out the house lights was over for the moment.
I backed up to 20 feet and loosed a second round. Again, the paper was hit and not that far from the first shot. Thus assured, I moved back to my rested position at 10 meters and started testing the gun and scope in earnest.
Today’s report is not going to end this test. Today, I’ll get the pistol zeroed for the accuracy test. I need the extra time to become familiar with holding a scoped pistol.
The Beeman P1 has two power levels, but I use high power because it’s more accurate than low power.
Finishing the zero
Back at 10 meters, it was time to adjust the scope. The caps come off and the knobs required either a coin or a screwdriver to turn. They have crisp click detents, so you know how far you’ve gone.
The reticles move in half-minute steps, but at only 11 yards there are still a lot of them required to move the strike of the pellet noticeably. After seeing the pellet move in the intended direction, I lost another fear that this scope would somehow not work as all other scopes had. It took about 10 pellets to get a reasonable zero. Then, I was ready to prove it.
Proving the zero meant a group of 10 shots, just like any air rifle would get. For me, it also meant learning how to hold the pistol to get the best results. I’m so used to holding handguns with one hand that any two-handed hold seems disturbingly complex to me. I know lots of people do it, and it can be very accurate.
I decided to use Crosman Premier lites for the sight-in, because I knew they worked well in my P1. They won’t cut a good hole in the target, but I’ll cross that bridge later.
I soon discovered that I should pull back with my left hand and push forward with my right, but I still need some practice. So the group below shows both potential as well as my not-yet-coming-to-grips with the hold, so to speak.
Ten Crosman Premier lites went into this target at 10 meters from the scoped Beeman P1 pistol. While this is not the best 10-meter pistol target I’ve ever shot, the group of five together under the 10-ring indicates this arrangement can work. The shots outside that group indicate that I still need to work on my hold.
What comes next?
This is a test of the BSA pistol scope, so that’s what I have to test. This first step taken today just got the scope mounted and started my education in using a scoped air pistol. I see that the hold is very important and also that it’s possible to do good work with the gun once you understand how to use the scope correctly.
I’ll also test the pistol with different pellets to see if I can find some good ones. In the past, I’ve used Premier lites in a P1, but I haven’t paid much attention to a P1 as anything other than a 10-meter target shooter. The scope will allow me to stretch out farther, once I learn how to hold it.
by B.B. Pelletier
Announcement: Due to a mix-up, the most recent Big Shot of the Week winner wasn’t announced last Friday. Jeffrey Aaron Demers is this week’s winner of Pyramyd Air’s Big Shot of the Week on their facebook page. He’ll receive a $50 Pyramyd Air gift card.
Today, I’m going to show you the new BKL adjustable scope mount that will soon be available. I mentioned this mount in the Part 3 test of the new RWS Diana T06 trigger last week, which is where the first picture comes from. I’ll show all the nuances of the new mount and discuss how it works.
Looking up from the underside of the mount’s rear ring, we see the two legs that slide up and down for elevation compensation. Note that the ring has two cap screws.
The front ring is captured, so all it can do is rotate as the rear ring goes up or down. This prevents stress on the scope tube.
These first two detail shots show how the mount works. The rear ring moves up and down on forked legs that are open on the bottom. Two screws on the sides of the legs jam the ring tight in position when the right elevation is achieved.
The front ring is captive and is only able to rotate when the rear ring moves up and down. This prevents stress on the scope tube.
The black elevation pad is a Delrin screw that the scope tube rests on. It’s located just ahead of the rear ring.
Another key feature of this mount is the elevation pad, located back by the rear ring. The scope tube rests on this pad, which is used to make very small adjustments to the elevation of the scope. A small Allen wrench inserted into one of the holes in the periphery of the elevation pad lets you turn it up or down like a capstan, providing tight control over the elevation changes made. When the scope rests on the pad, it provides additional support against random movement once the scope ring screws are properly locked down.
Does it work?
I tested this mount on an RWS Diana 34P that I’ve retained for tests just like this. The rifle in question has 21 inches of droop at 20 yards (the only sight-in distance I use, since the pellet strikes the same place as the 30-yard point of intersection when it crosses the line of sight for the second time), making it a severe case of barrel droop. When I developed the UTG droop-compensated scope bases for RWS Diana spring rifles, this rifle was the worst test case, against which the base for the RWS Diana 34 base was designed. If the BKL mount can fix the droop on this rifle, it can fix anything you’re ever likely to encounter.
And fix it, it did! With the mount adjusted about as far up as it could go and still be locked in position, the scope was sighted-in dead-on at 25 yards, which is in the center of the 20-30 yard sight-in distance. And, the scope was in the center of its click-adjustment range. This was an acid test that the BKL mount passed with flying colors.
Another factor I was watching was the BKL mount’s ability to hold its position on a heavy-recoilling spring rifle. When the mount was given to me for testing, it had already withstood the jackhammer recoil of a Hatsan 125, which is even harder on scopes and mounts than the UK-produced Webley Patriot. Indeed, the scope that had been in that test was destroyed, but this mount held fast.
On the RWS Diana 34P, the mount also held fast under two different scopes, the intial one that finally gave up the ghost during my test and the replacement scope. Hundreds of test shots were fired without a hint of scope mount movement or scope movement in the rings. Despite there being just two screws per scope cap, both scopes remained in place throughout the test.
This mount also offers 11mm dovetails on both sides of its base. If you want to attach a laser, tactical flashlight or rangefinder, your base for them is built right into the scope mount. Because BKL recesses the Allen screw heads into the base, both sides of the scope base have this feature and can be used in this way.
Here you can see one of the two 11mm dovetails in the base of the BKL mount. There’s another one on the other side, and recessed screw heads make it accessible for this purpose, as well.
The final feature this scope mount offers is the facility to mount a bubble level to the base of the new mount. It attaches to one of the three spreader holes in the base, though I think you’ll choose the hole that’s farthest from your eye so you can focus on the bubble. I used this level in the test of the RWS Diana 34P, and it worked well.
If you need to spread the base of the mount to get it on a gun, the ring screws also have to be loosened. Then, the base can be spread evenly by the three spreader screws.
The best part
I’ve saved the best for last. When this mount was shown to me at the BKL factory, I was told that the motivation for making it the way they did wasn’t an air rifle, but a popular air pistol! The cuts on the mount are specific to clear the front sight on the Beeman P1/HW 45 spring air pistol.
The profile of the new BKL adjustable rings was made to accommodate (to clear) the front sight of the Beeman P1 pistol.
Because this is the first mount I’ve seen that was made for the P1, I think I’ll order a BSA pistol scope and give it a test. Whatever scope you select has to fit into the two rings that measure 4.0625 inches apart on the outside. Because this is a one-piece scope mount, those rings cannot be moved, so pick your scopes accordingly.