Posts Tagged ‘BKL 1-piece mount’
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.
It was another calm day at the range last week when I tested the TalonP air pistol once again. This time, I had a couple special goals. One was to see if the new method of scope mounting recommended by AirForce owner, John McCaslin, would help me hold the gun better, and the other was to test the velocity of the gun with the most accurate pellets on power setting eight.
New scope mounting method
The scope has to be moved forward for increased cheek contact with the reservoir/tank. You know that I’m now using the optional shoulder stock extension that clamps onto the pistol’s reservoir. The way it clamps gives you a wide range of pull lengths. I need a longer length of 14.5 to 14.75 inches, so I have the extension way out at the back of the reservoir, but most shooters will slide it in a bit. John recommends that you adjust the stock first then position the scope where it needs to be for your eye. He recommended a BKL cantilever mount that pushes the scope forward. I used their BKL 4-inch one-piece mount with what they refer to as drop compensation, which actually means droop. Because the one I had on hand has one-inch rings, I had to say goodbye to the superb Hawke 4-14x42AO Sidewinder Tactical scope I’ve been using and substitute a Leapers 5th Gen 6-24x50AO scope. While it was entirely adequate, I have to observe that the Hawke at 14x was clearer than the Leapers at 24x.
The first time around, the Hawke scope was mounted on two-piece BKL mounts that were slid as far forward as possible. The image was still too close to my eye to resolve to full size, so I needed to move the eyepiece of the scope forward about another half-inch.
Sight-in took longer because, at this rifle range, I don’t have the ability to place a small target at 10 feet. I have to mount all my targets at the 50-yard backstop. So, I mount a two-foot by four-foot silhouette target on the backstop with its plain, light backside facing me. Then, I place the sight-in target in the center of that, and usually I can catch the pellet holes somewhere on that huge piece of paper. You could use cheaper paper for this — just as long as it shows the pellet holes clearly. I’ve never used a scope collimator, and I don’t intend to start now. This is so much easier!
I hadn’t changed the power setting from the last test, so the performance went the same as before; this time, I cut off the fill at less than 2,700 psi. That allowed me to start shooting a group in three shots. As I learn this pistol, I’ll eventually learn exactly where to stop the fill so shot one is right on the money every time. However, as with most airguns — including springers — you have to “wake” the gun with a couple shots each new time. For hunters who spend hours between shots, this can be daunting; but very few guns will put the first shot in the same place as the others after a long period of rest. It’s true of firearms, as well, so I guess it should also apply to airguns.
How did it do?
Nothing really changed from the last time I tested this pistol. Now that I have the air fill down pretty well, I can even do “tricks” with the gun. Let me demonstrate with JSB Exact Kings and Benjamin domes.
50 yards: Five JSB Exact Kings in the hole below and two above. The five-shot group was 0.246 inches between centers. Add the other two shots, and the group grows to 0.577 inches between centers. Even that is better than most .25-caliber air rifles can do at 50 yards; but the point (trick) is that I knew those last two shots were going to stray, and I didn’t have to shoot them.
50 yards: Five Benjamin domes in the hole on the right and then I shot a sixth that I guessed would stray. Stray it did, but to the left this time, where in the last test Benjamins moved to the right. Go figure! The tight group measures 0.38 inches. With shot six, it opens to 1.059 inches.
Technique is important!
Lest a new airgunner buy this airgun and splurge on all the support equipment to operate it (basically just a carbon fiber air tank), and then buy the same exact pellets I’ve used in this test, only to be disappointed that he cannot replicate what I’ve done, allow me to show you how I’m able to do what I’m doing. It’s not a trick, but it does require an advanced shooting technique of which a new shooter is probably not aware. You will remember that I mentioned my intention to mount a scope level on the gun last time. I forgot to do that, but on a printed target there are plenty of references to help me control the amount of cant (the amount the rifle is tilted to one side) for every shot. So, for the two groups I’ve shown you thus far, I watched the visual cues as precisely as I’ve been watching the bubble level in the Pellet velocity versus accuracy test. Let me show you what it looks like when I ignore these cues and just shoot when I think the airgun is being held the same every time. I’m trying just as hard to shoot a good group, except I’m ignoring the one variable of cant.
50 yards: This is what you get when you don’t pay attention to cant when shooting an accurate pellet at 50 yards. Five JSB Exact King pellets made this 0.747-inch group. That’s still a very good group for a .25-caliber airgun at 50 yards, but it looks large in comparison to what I’ve shown you previously in this report.
I tested the velocity of this pistol with several pellets back in Part 2. That was when we confirmed that the TalonP isn’t just capable of hitting 50 foot-pounds at the muzzle — it can actually shoot a string of 10 shots above that energy figure.
Today, I’ll give you the velocities of the two most accurate pellets. I’m doing this for one reason. The 43.2-grain pointed Eun Jin pellets that are required to achieve that bragging power are not the most accurate pellets in this airgun. The two I’m showing today are, and they’re best at power setting eight. This is a real-world look at what the pistol can pump out when it can also keep five pellets inside a wedding ring at 50 yards.
JSB Exact Kings
The gun was filled to 2,700 psi and shot over an Oehler chronograph. The average velocity of JSB Exact Kings for the five best shots was 875 f.p.s., with a low of 860 and a high of 892 f.p.s. At the average velocity, the muzzle energy is 41.66 foot-pounds. So the total spread of velocity for the pellet that would put five under a quarter-inch at 50 yards was 32 f.p.s., but you can see that it doesn’t really matter that much.
If I had included the very first shot fired after the fill, the velocity was 844 f.p.s. and the next shot was even slower, at 836 f.p.s. I got a total of 11 shots on a fill, the last of which went 841 f.p.s. I’ve shown you both last time and today that there are five screaming shots within this larger string that I know for certain will be accurate if I do everything right. Do you want to kill the woodchuck at 60 yards, or do you just want him to envy you?
I refilled the gun to 2,700 psi and shot a string of Benjamin domes. They averaged 877 f.p.s. with a low of 840 and a high of 902 f.p.s. That’s a 62 f.p.s. spread, yet you can see what they did on target. This pellet generates 47.49 foot-pounds at the average velocity. Looking at the total string, shot one went 783 f.p.s., and shot 11 went 827 f.p.s. Those shots are outside the string that gives the best accuracy, and you’ll break your heart by hoping to get them to go into that tiny little group. Take your five great shots, or think about buying a different pellet gun.
You won’t find another pellet pistol that will touch this one for power and accuracy at this range, and many pellet rifles will fall behind as well. The TalonP air pistol is not for everyone. It’s for the shooter who has the heart of a buffalo hunter. The one who knows exactly what his gun is capable of and is willing to invest the time and care to get it.
Airgun hunter, Eric Henderson, has already taken a prairie dog at 100 yards with the exact same pistol I’m testing for you. I’m not the only one getting these great results.
What I’ve done is take the time to decode the operation of the gun and find two good pellets for it. I’ve told you the best fill pressure, which is way less than what the factory recommends. I’ve given you the power setting, which is under the maximum setting.
The TalonP is a thinking shooter’s airgun. If you want the most accurate and most powerful smallbore air pistol in production today, here it is.