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.
60 thoughts on “New BKL mount adjusts for barrel droop: Part 2”
Please do a write-up on taming the twitchy ones! Yet another facet to airguns that needs written.It’s amazing that theres anything left thats not been covered! But there is so much.I took apart the HW54el Barakuda today……was suprised there is so little on the web about it.I really had no idea what the piston & seal were supposed to look like! Good old HW and the loads of caked grease….you ALWAYS know when you’re the first one in one.It took 2 messy hours to get down to just cleaned parts.The leather seal looked great…….but the piston was a mess.I chucked it in a drill and spun it till it was smooth as glass where needed,using large pieces of sandpaper on my open hand.Gotta really watch the fingers on the cocking slot though.It shoots much more solid now……the parts are getting along better.The safety now works…..it was inoperable because of the dried grease.Fun stuff.
That HW grease is just fine until it gets old. Guess you are supposed to take them apart, clean them, and re-grease them every so often.
I send a couple of messages but they did not go through. I was looking for the name of that oil you use in PCPs as I have just aquired a FX Monsoon. Lots of digging Pellgunoil! How much and how often do you use it?
Pity I cannot buy the US PCPs you recommend here in Oz as there are no agents I know of.
Don’t use Pellgunoil for the Monsoon, of course. You want a silicone oil with a high flashpoint. Add a drop to every 10th fill and that should be enough. To be honest, I seldom if ever oil my PCPs. They just never seem to need it.
I just replied to my test to see if it got through and it did not. See if this works
Four attempts and can’t post
Bob from Oz,
I’ve added you to the whitelist for comments. Not sure why your posts were caught up by the spam filter. All have been approved now. Let’s see if it happens again.
Wouldn’t this ring design keep the scope rings nicely “optically centered” above the boreline? (This would of course assume that the dovetails are cut above centerline too which may not always be true.)
For a bit wider, or a bit narrower, than 11mm this would seem to be a nice feature of the design.
I don’t quite follow you. What does optically centered mean in reference to a scope ring?
I meant that the centerline of the rings would over the centerline of the bore.
I’m with Frank on the twitchy gun help idea for a blog.
BKL droop mounts….
I have two of the non adjustables. One on R7 #2 and had one on R9#2. The one on the R7 is O.K. . The one on the R9 wanted to creep. The POI kept crawling. The creeping was very slow and was hard to detect. I cleaned the grooves and mount with Gun Scrubber and tightened the mount as tight as I dared. I was afraid of stripping the screws. The mount has to be squeezed a lot to fit an “R” gun.
Then the scope started to creep.
Try constantly adjusting a Leapers that uses a allen wrench to unlock the turrets. I was Pi$$*d off big time.
Said to hell with it and undrooped the rifle. Installed a pair of rings with a stop pin and anti-slip tape. Stuck on a Hawke scope, and promptly broke the scope after a few shots. The front lens chipped.
Replaced the scope with another Hawke, and slapped in a Vortek kit. Still need to do an outdoor zero, but looking good right now.
I don’t know which BKL mounts you used, but the ones that were made by the company before AirForce bought them didn’t work. I proved that repeatedly in several tests. I believe it was due to lax attention to the specifications during manufacture and no quality control.
Once AirForce began making the mounts on their own machinery (after they assembled all the finished parts they got in the deal) the rings started working as advertised. So anything i say about BKL mounts only applies to those that are made by AirForce today.
So older BKL mounts are always suspect, as far as I am concerned.
Don’t know if this means anything…
These mounts have 6 screws down the side, and use caps with just 2 screws (not 4).
Don’t know if I still have the box the last one came in. Probably don’t say who made it anyway.
Well, since other companies have been copying the B-Square design for about 3-4 years, you could have almost anything. I know one of the companies that copies the B-Square designs and their products are all suspect. The owners know very little about airguns, nor do they care. They are just salesmen who think one product must be as good as another. So as long as the price is the lowest on the market, they continue to sell their fake stuff.
Can’t find the box. Must have tossed it. Have a pair of risers made in Ft Worth.
The drooper has the extra holes in the opposite side for stretching it open. Also has some little notches on the jaws.
Not going to worry about it any more. If the R9 can hold for a tin or two of pellets I will consider it good.
Dang. That is frustrating. These endless strings of mishaps that happen sometimes make my head want to explode.
It sounds like you got a handle on it. Incidentally, the Centerpoint brand of scopes are good one to try. They are much like the leapers, but have knurled rings that are hand tightened to lock the windage and elevation settings on most of their models.
If you are talking about the 4-16x from WW, then forget it. I have busted two of them already. They also have a bad habit of geting sticky in cool weather….makes adjustments a pain.
The R9 (.22) is working good inside right now. Think I have finally got it in the bag. I also re-torqued the mount screws (caps) after a day or two. The tape compresses in a day or two and the screws will need tightening again. They seem to be stable (scope won’t start creeping) after that.
One of the last times shooting in the basement (9.5yds) i was shooting a page of card stock for a target. Get fairly clean holes. Burning up some RWS SHP to get some rub in time on the Vortek.
Shot a hole in a clean area to use as an aiming point. With the Hawke set to just a little over 3x and using the first mark below center (map 6) I shot 3 or 4 more pellets at the first hole. Resulting hole measured at the edges of the lead marks as best I could came out… .221″ wide and .242″ high. Not much need to subtract a pellet width for this one. Also, the AO does not quite focus this close.
Have some 5.53 FTT that I need to try out. <10fps max spread (10 shots). They give up about 1/2 ft-lb to the strongest shooting pwllets, but close enough . The chrono looks better with the FTT. Better B.C. too.
I did buy one from Wally. I bought the other three Centerpoints came from PA. I haven’t had a problem yet, and one of them is mounted on my most powerful springer, a Diana 52 in .22.
On the other hand, once a company gives me a raw deal, and won’t work with me to get a resolution, they can go straight to hell as far as I am concerned and will never receive another dollar of mine. No amount of slick marketing or fake sucking up can dissuade me. So if you are soured on them, enough said.
Big box retailer Circuit City went out of business not so long ago. I like to think my ill will had something to do with it.
Maybe yours combined with mine and became REALLY caustic! I bought a car subwoofer from them,and sprung for the “extended warranty” for about 20$…….speaker blew at well less than the RMS rating.No big deal,right? WRONG! The guy at the return counter,which I arrived at within a half hour of the speaker failure,says “I have to have our tech look at it”……he comes back and tells me it’s not a warranty issue,our tech guy SMELLED it and “it smells burnt” so it isn’t covered! I went insane,right there at the counter.How did that guy “qualify” for the title of TECH????? YES,I was very glad they went bankrupt…….Darwin insisted 🙂
All this time… I thought it was just me. I should have known you were in on it all along. If we united to meld our scorn upon more evil doers, the world would be a better place.
We can do that….but first I must insist on a cape!
I was searching the blog archives the other day for something and ran across part one of this test and thought, “Wow, those rings look like nicely engineered and well made.” I remember trying the adjustable B-Square mount with the pointed setscrews on my RWS54 years ago and not having much luck making them work properly. This BKL setup looks first class.
There are two or three levels of quality among B-Square adjustable mounts.
The ones I raved about were made in Fort Worth when Dan Bechtel owned the company. Those are the good ones. Then there are the ones made after the company was sold. Some are good and some aren’t. But they are mostly still very good.
Then the company exported the design to China and the quality went south right away. Those are the ones being sold today. Good luck getting them to work as advertised!
I purchased a set of these B square adjustable mounts. It has 3 different sizes of allen head screws to mount and adjust them. How convenient. The screws that get adjusted the most are made from aluminum, and very thin, so stripping them is a certainty. I finally buckled down and purchased the somewhat pricey Beeman/Sportsmatch adjustable sight. I haven’t looked back since.
I was searching the blog archives the other day and ran across part one of this report and thought, “Wow, those rings look nicley engineered and well made.” I remember trying the B-Square adjustable mount with the pointed set screws on my RWS54 years ago and not having much luck getting them adjusted properly. This BKL looks first class.
BB, Yes on the “twitchy gun” write up! Weird that the Slavia has it’s own rule when using measurements. I would think it important to label a 14mm mount 14mm, not 11mm to be ‘like the rest’.
Shot my father in laws Nitro Venom yesterday. It’s smooth, quiet and powerful. Good looking gun, nice stock and decent (painted grain) finish. The included CenterPoint scope is better than fair, and the trigger is absolutely horrible, with take up measured by the yard and inconsistent let off points. We didn’t have time to get into the manual to see about adjustments, but there is a screw behind the trigger and I’m guessing there is some adjustment. It’s a nice rifle though and for the $129 deal he got it’s the bargain of the year!
I forgot to mention, shooting the gas spring powerplant is a pleasure. There’s still quite a bit of recoil, but I’m impressed, as that ‘s the first time I’ve shot one. I like shooting the old Gamo CFX less than before, and regret not having PA do the conversion. I see it getting done in the near future.
You shouldn’t feel any recoil from your rifle. If you do you’re holding it against your shoulder too hard. Try softening your hold and see how that feels.
A gas spring can give you a headache in only a few shots if you clamp down on it. Or it can fire without notice if your hold is light.
He brought out his old Gamo 220 Hunter also, maybe that was what was recoiling so much. Yes, a loose hold. That is my hardest thing for me, for some reason I struggle with that more than anything. Need more time behind the trigger.
B.B., you’ve made me feel so much better.
I’ve struggled all year with my 631 and just could not figure it out.
At 10m it will put 5 shots in one hole.
At 20 yards it will put 5 shots in a dime.
But at 30m (which I thinks is a good test of a low/mid powered gun like the Slavia) it shot 1″ groups on a good day…and man, I tried every trick I could think of.
I think it is capable of 1/2″ groups at that distance…I can’t wait to see your bag of tricks 😉
I’m working on the Bag O’ Tricks report but as you have noticed, I haven’t gotten there with the 631 yet. Sometimes there ain’t no trick that works. But I haven’t given up yet. The work I did with the Accuracy vs Velocity test has shown me a lot is controlled by harmonics. Perhaps that is what we are dealing with here.
Not so sure that the “cone of fire” notion holds that far out. Harry (Yrrah) on the yellow has theorized that it isn’t “IF” but at what distance pellet flight falls apart. The gist is that at low velocities there isn’t enough drag to stabilize the pellet against a slow speed precession. So the pellet starts to develop a curved path which is similar to a curve known to mathematicians as a conic helix. (A conic helix is a helix of increasing diameter.)
One way to test would be to use a camera that can take 400 frames per second or so and look at the pellet’s flight before impact.
Another would be to increase the distance again. So if you go to 40 or 50 yards the group size should get very much worse. So if you get 1″ and 30 yards by the linear geometrical relationship you should be getting 1.3″ at 40 yards. I’d guess that you probably get more than 2″ at 30 showing that the linear geometric relationship has broken down.
Food for thought anyway…
The 400 frames per second is good enough because you film from the shooting position to the target. So you’re watching the precession of the pellet from the rear, not its spin or its forward velocity.
If you tried to film the pellet as it was whizzing by, then you’d have to have a much much faster frames per second in order to even see the pellet. The 631 starts off maybe 600 feet per second and would be may 350-400 at 30 meters? So at 400 frames per second the pellet goes forward one foot per frame.
Ugh… Last sentence should be:
I’d guess that you probably get more than 2″ at 40 showing that the linear geometric relationship has broken down.
Disappointed that the jsb rs pellets didn’t work well in the 631. They’re far and away the best pellet in my slavia 634. That’s a springer for ya.
The thing that sits on top of my Bag-O-Tricks for a twitchy breakbarrel is Cleaning the Barrel with jb bore paste.
This just proves that every gun is different.
Hobby’s/Meisterkughlen and JSB Exacts were all giving me inch and quarter groups or so.
When I switched to the Exact RS (7.3 vs 8.4gr) it immediately knocked the groups down to a consistent 1″.
Not bad…I figure that it means I could safely take out a magpie if I was being threatened 😉 but I’d really like to see some of those mythical 3/8″ groups that are so often spoken of.
Funny…I’m complaining that the Slavia will only shoot 1″ at 30m…yet according to some of the stuff I’ve read the new Savage we just purchased may only get 1″ groups at 50yds unless we use match ammo (which from what I understand is pretty scarce in WMR).
We really are spoiled accuracy wise with our airguns at shorter ranges.
It’s in there already!
As for the accuracy, Mac suggested something that I may try. It’s some kind of synthetic damping material used on bows and rifles to deaden the vibration patterns.
Know anything about it?
Maybe. I don’t know yet. But it works on bows and firearms.
I remember that you had to do some work on this rifle some time ago. Did you replace the mainspring? I am thinking that the spring might be too stout for this rifle if you did. My 631 has two things going for it that make it as enjoyable as shooting an R7. First is the near dead shot cycle. It is calmer and quieter than most of my R7s. Second, it came with a set of match sights that are high quality with crisp adjustments, despite being made in China.
Like Kevin, I purchased a newer Slavia 634. The dovetail is the ‘standard’ width on this one, so I had no problem mounting scope rings. Even with the higher power of the 634 as compared to the 631, it is not anywhere close to being twitchy. Then again, I did install the highly vaunted “Milan beer can mod” in my 634 to tighten the fit betwixt the piston and spring. While I had it apart, I drilled a couple of holes for scope stop pins just for kicks. These Slavia/CZ rifles are priced so low in comparison to their value, it is obscene.
No, the mainspring is original, I think. The rifle still cocks easily.
My 631 isn’t twitchy at all. I normally get a bout a dime at 30m. And it’s nothing to do with my ability. I ain’t good enough to supplement for a twitchy gun.
Maybe it’s a QC issue?
I don’t think I would get the groups within the groups if the problem was poor quality. I’m pretty sure that there is a bad harmonic here.
I remember a test that Mac was doing for you, and he paid attention to pellet fit. Difference in fit can cause “groups within a group”.
Funny things happen.
AA 4.51 and 4.52 pellets weigh the same, feel like the same fit, but show way different chrono spreads and group sizes (R9 #1).
4.50 FTT show noticeable velocity difference when sorted .1 grain increments. (R9#1)
Maybe a very touchy power plant is what’s biting you. Unforgiving power curve.
It could be. But I am formulating a plan to see if I can change the rifle’s shooting capability. If so, I may have the solution.
Hope so. Will be waiting to see what you try, and what the results are.
Put me down for another vote for the twitchy gun fix blog…
Stop gorilla gripping.
You know, a bottle of Beam (black) and coke goes pretty fast when you mix it yourself? And that damn subwoofer keeps trying to slide off the shelf. Still have some leftover tool box no-slip liner to fix that.
P.S. No straight answers until tomorrow.
My Ruger Air Magnum is both hyper-twitchy and severely droopy. Unfortunately, it came with a Weaver base. Are there Weaver rings that I can use to compensate for droop?
Also, would twitchiness only be a function of harmonics? I’d imagine that barrel harmonics come into play because of mechanical impulses that get dissipated, in part, along the barrel as a transient response. I can see applying something to dampen this transient wave, but if the mechanical vibrations caused by the spring are too great, that wouldn’t be enough. Seeing what happens when I try to lock down a powerful springer tells me that there are hard jumps that can’t be accounted for with dampening, and so we apply the “artillery hold”. I’d imagine that the only real solution for such a gun would be to tune the entire thing, including control over the range of motion of the spring along the plane orthogonal to the springs expansion.
My Ruger Air Magnum is the wild child in my family that I refuse to abandon. The only harmonics that it seems to be in tune with is garage quality punk rock. 🙁
Yes, there are Weaver mounts that compensate for droop, but unfortunately all of that is in their bases. I don’t know of any rings that compensate by themselves.
Of course your Ruger was made in China for Crosman and is part of the Benjamin Trail specification. And because it is a magnum breakbarrel it is going to be super-hard to shoot. De-tuning is a possibility, though success isn’t guaranteed. I detuned my R1 and got mediocre results. And I haven’t shot it enough to really say whether the detune was a success or not.
UNCLE B.B. I REALLY ENJOYED THIS BLOG. IT HELPED EXPLAIN WHY I AM HAVING A PROBLEM SHOOTING MY SLAVIA 634. IF YOU HAD A PROBLEM WITH YOUR 631 I KNOW IT IS THE RIFLE AND NOT JUST ME. THE 634 IS MORE POWERFUL THAT THE 631 BY ABOUT 200 FPS. I DID TRY A 14MM BKL MOUNT ON MY RIFLE AND FOUND OUT THAT IT WAS TOO WIDE TO FIT THE GROOVE ON MY RIFLE. I SWAPPED OUT THE MOUNTS FOR 11MM ONES AND THEY FIT. I HAVE A NEW 634 WITH A SYNTHETIC STOCK AND SLAVIA COULD HAVE CHANGED THE WIDTH OF GROOVE TO BE IN LINE WITH STANDARD 11MM ONES. I HAVE SHOT THREE PELLETS INTO ONE HOLE BUT THE OTHER TWO OPENED THE GROUP TO 5/8 OF A INCH. I HAVE SOME 5 SHOT GROUPS THAT WERE 4/10 INCHES BUT THEY ARE FEW AND FAR BETWEEN. I AM SHOOTING AT 50 FEET WITH A APERTURE SIGHT. I WILL SHOOT ON AND KEEP TRYING TO IMPROVE. I AM WAITING TO SEE IF YOU FIND A TECHNIQUE THAT WILL WORK.
As soon as I find out what works I will let you all know. Apparently this model does have this problem.
Do you know under what model number are these 14 mm barrel drop adjustable mounts sold?
On BKL’s website the only one I can find is BKL-460 but these don’t have the barrel drop adjusting screw near the rear ring just like on your picture. Still the BKL website description says that the 460 mounts are drop compensated. Any thoughts?
The number is 4134 for the one-inch and 4135 for the 30 mm.
Thanks very much for the info. Strange though that this model numbr isn’t recognised on BKL’s website as far as I can tell. Probably this is also the reason why I’m not able to get these here in the UK. Not even searching ebay 🙁 Do you know if is this model is a limited one or limited to US market only?
That was a Pyramyd Air website number I gave you.
Ah I see BB, the original BKL model number is BKL-288. Still impossible to find these in the UK 🙁
I might give a try and order it from pyramidair.
Here are the links:
1″ rings: https://www.pyramydair.com/product/bkl-1-pc-adjustable-scope-mount-1-rings-3-8-dovetail-black?a=4134
30mm rings: https://www.pyramydair.com/product/bkl-1-pc-adjustable-scope-mount-30mm-rings-3-8-or-11mm-dovetail-black?a=4135
I googled the model number and indeed found it on pyramidair’s website. Strange that it isn’t listed on BKL’s website.
Seems that the US market has limited access to Slavia 631 model but on the other hand accessories just like the 4134 are very difficult to find in here in the UK.