Posts Tagged ‘bubble level’
by Tom Gaylord, a.k.a. B.B. Pelletier
This report covers:
• Why does a scope need to be leveled?
• Scopes cannot be leveled.
• A leveling solution.
• Bubble levels.
• What works
• What about a collimator?
• My moment of enlightenment.
I promised this report to blog reader Genghis Jan over half a year ago. Several times, I’ve started to write it and turned away, but today I’m seeing it through.
Why level a scope?
There are 2 reasons for leveling your scope. The first is psychological. If the reticle inside the scope appears to be slanted to one side when you mount it on your gun — and I am primarily talking about rifles today, although these principals apply to scoped pistols just as well — it’s disconcerting. The second reason for leveling a scope is to ensure the vertical adjustments move the strike of the rounds vertically, and the horizontal adjustment do the same. If the scope does not appear level, the adjustments will move the rounds off to one side or the other as they move up and down.
If a scope’s reticle appears tilted, do you then tilt the rifle sideways to level the reticle? Or do you just hold the rifle so it always “feels” level and tolerate the reticle that seems tilted? I’ve tried both, and neither one is as comfortable as having the scope aligned perfectly — so it appears level when the rifle is held comfortably. But, just so you know — both solutions will work because there’s no such thing as a level scope.
Rifle scopes cannot be level
Sorry to disappoint, but there’s no scientific way to ever level a scope to a rifle — at least not to any rifle that has ever been made. I used to be a tank commander; and on occasion, there are reasons to level the tank cannon. But there’s nothing on a tank cannon that is level. So the makers did something about it. They machined several pads on the breech of the cannon where a precision level can be stood. This level — called a gunner’s quadrant — has “feet” that are steel pads machined into it. Their purpose is to stand the quadrant on the machined pads of the cannon’s breech and establish a level.
Without these machined pads, there can be no point on the cannon that is level. What I’m saying is that there’s no spot on the mechanism that’s true enough that a bubble level placed upon it would have any meaning. It might be possible to get the bubble centered on the gunner’s quadrant, but you could never be sure of doing it again with the same results. But with the machined pads, you have what you need — a reference point — to declare the gun to be level.
Level is a relative term
You see, the term “level” relates to the earth. An item can lay on apparently flat ground and not be level according to its bubble or the center of its plumb bob. Reference points are needed. And no rifle I have ever seen has them. Therefore, no rifle can ever be level! Please think about this before you comment.
I’ve used several leveling solutions in the years I’ve been mounting scopes. One was to hang a plumb bob from a target backer at 50 yards and align the scope’s vertical reticle with it once the scope was mounted on a rifle. I thought this would guarantee that the scope was level. Maybe it did, but it often put the scope at odds with the rifle because the rifle’s scope base was not machined so the scope appeared level when aligned this way. I actually shot several rifles with what appeared to be a slight cant in the scope reticle because I had aligned the scope in this fashion. The things that crazy people will put up with to maintain the universe they create!
A plumb line has been suspended from a target backer at 50 yards (left). Now, the scope (right) will be superimposed upon it and the vertical reticle will be aligned with the plumb line.
The scope has been shifted over the plumb line and rotated in the rings until the vertical scope reticle is aligned with the plumb line.
Neat trick! Is the scope aligned? Yes, it is. Is this the best way to do it? No, it isn’t. Let me show you why.
Now, this is what you may see when you hold the rifle to your shoulder. It may not be as obvious as this, but unless the scope mount was machined exactly with regards to the plumb line, you’ll notice the tilt and it will bother you. Are you then supposed to hold the rifle “level,” or do you “level” the reticle before shooting?
I’m showing you what happens when you attempt to level the scope by outside means. Sometimes, those processes guarantee the scope will not appear level when you hold the rifle in your arms.
Another method that doesn’t work
Some folks will purchase a bubble level for their guns, mount it and declare the job done. Of course, there’s no reference point on the gun that they can refer to, which is why I told you about leveling tank cannons at the start. Doing it this way is like driving a car in dense fog by keeping the fenders between the turn signals!
The bubble level is a wonderful tool but not for leveling scopes! It’s for leveling shooters in the field. Once the bubble is level, you know the scope is aligned the same as when it was sighted in on the bench (as long as the bubble was level at that time).
Here are two different kinds of bubble levels being tested on my Whiscombe rifle. They help to level the rifle in the field — not to level the scope during mounting.
Genghis Jan — this is the only way to level a scope. Mount the scope on the rifle and turn the tube until the vertical reticle appears to bisect the rear of the rifle.
You extend the vertical reticle line downward and see how it looks against the back of the rifle. When the vertical scope reticle appears to bisect the centerline of the rifle, the scope is level.
You can argue that this is an imprecise method of doing this, and I cannot defend it. Because — as I have already shown — there is no such thing as a level scope. Level with what?
But here is what I do know. The scope will never look right until you level it this way. If you pick up the rifle and the scope appears to be canted to one side, how does that make you feel? It’s that feeling that either inspires confidence or instills doubt, and these two emotions will drive you to success or failure while shooting.
As you gain experience with your rifle, your hold may change, and you may need to adjust the scope, again. After that, you probably have to sight-in once more. I’ve had this happen to me several times with different rifles.
What about a collimator?
You’ve heard of an optical device called a collimator that magically aligns scopes for rifles? Gun stores use them, don’t they? Yes, they do, but not to align the scope reticle — not to level the scope. They use a collimator to align the axis of the barrel with the scope’s line of sight — so your bullets land on paper at 50 or 100 yards when you go to the range.
But an airgun can be sighted-in at ranges much closer than 50 or 100 yards. I usually start at 10 feet. I wrote an article about sighting-in this way that you really should read. Adjusting a scope so it looks level has nothing to do with sighting-in unless the scope does not appear to be level to you, and then you won’t be able to adjust it properly.
My moment of enlightenment
You may well ask why it took me so long to write this report, when it seems so simple (and really is!). It is because I know that the simplicity of this will offend many people who believe that leveling a scope must be a complicated procedure. Some will refuse to believe me and will insist they level their scopes by the methods I’ve written about or by some other process.
I believe that this step is why many buyers shy away from buying scopes for their guns unless they are mounted by the factory. Well, guys, I used to BE the factory! That’s right. For three years, I mounted every scope that was mounted on an AirForce air rifle and then I zeroed it. I learned how to mount scopes the best way, which is also the quickest way, and additionally it’s the only way that will ever satisfy the user of the rifle.
I’ve had to adjust scopes (rotate their tubes in the rings slightly) that others have mounted to get their crosshairs in line with the vertical axis of the gun. If you’ve owned many guns with scopes, I’m betting you’ve done this, too. When you do, you’re simply doing what I said to do several paragraphs previously.
I know this sounds too simple and too unsophisticated to work; but believe me, this is the only way it does work. As you gain experience with scoped airguns, the truth of this report will become increasingly evident.
by B.B. Pelletier
The FWB 300S is considered the gold standard of vintage target air rifles.
This is a test I said I would do the next time I got a calm wind day at the range. That day came last Friday, and I took the opportunity to test the FWB 300S at 50 yards with a scope. This test was designed to see if there is any discernible accuracy difference between pellets that are sorted by weight and those selected at random from the tin. If you read part 4, you’ll see that I was surprised to find that these JSB Exact RS pellets I selected for their accuracy had such a variation in weight. I sorted through almost 40 pellets to find 20 that weighed exactly 7.3 grains. Though the weight difference was only four tenths of a grain, it was more than expected and more pellets were affected than I thought.
The JSB Exact RS pellet was chosen because of previous performance demonstrated in part 3. And I had to choose a domed pellet because out at 50 yards no wadcutter can possibly be accurate — I’ve proven that on many occasions in the past.
In part 4, I tested the rifle at 50 yards using the target sights that come on it, and I got two groups of 10 shots each. One was with random pellets taken from the tin. That group measured 1.689 inches between the centers of the two widest shots, while the other was 10 weight-sorted pellets that grouped in 1.363 inches. I didn’t feel that test was conclusive, so I wanted to return with the rifle scoped to see what it could do.
Not only did I mount a scope on the rifle, I also installed a scope level, and on every shot the bubble was leveled. That eliminated the possibility of any cant, so the rifle was always shooting in the same orientation.
The scope hangs over three-quarters of the loading port, making loading a chore. Notice how close together the scope rings are, yet they occupy the entire length of the dovetails. The 300S is not made for a scope! Notice, also, the scope level that was consulted on every shot.
I mounted a Leapers 3-9×50 scope with AO. It’s an older version of the one I linked to, but the specs are mostly the same. Notice in the photo that this scope was almost too long for the rifle, even though it was mounted at the extreme rear of the spring tube.
Where I had used a 3-inch bull target with the aperture target sights, I switched to the smaller 10-meter target when using the scope. The pellets were falling off the target paper anyway and onto the plain backer paper attached to the target frame, because of the large drop of this pellet at 150 feet.
I couldn’t have asked for a better day in which to shoot. Since I was at the range very early, there was absolutely no breeze. The sun hadn’t risen very high, so I didn’t need to shield my non-sighting eye. The rifle rested in the bunny bag dead calm, so altogether this was as perfect a test as I could have run.
Bore already seasoned
Because the bore had been shooting JSB Exact RS pellets last, it was already seasoned for this test. Still, I did shoot the rifle a few times to wake up the action. Then, I began the first group of unsorted pellets.
This time, the pellets did very poorly — grouping 10 shots into 3.152 inches at 50 yards. The group is very elongated, looking like a large velocity swing. The group measures just 1.178 inches wide, which is less than half the height.
Next, I shot the pellets that were sorted by weight. Ten went into a group measuring 1.606 inches across. This group is fairly round and well-distributed, so it makes me wonder all the more about the first group. Perhaps the gun needed longer to warm up for the first group than I allowed?
Test is not conclusive
I’m declaring this entire test invalid. I think I’ve stretched the FWB 300S beyond its capability, and the results are not telling me what I need to know. I’m aware that others have shot 10-meter rifle at 50 yards and say they’ve gotten good results, but clearly I’ve not been able to do the same with this rifle.
I think the test itself is worth pursuing, but with a rifle better-suited to accuracy at 50 yards. Pushing the FWB 300S outside its comfort zone was not a good idea. But I have several accurate air rifles that are all capable of grouping well at 50 yards. That’s what I need to rerun the test.
by B.B. Pelletier
The FWB 300S is considered the gold standard of vintage target air rifles.
Before we start, a word about some of the airguns shows that are coming up. First there is this:
Pacific Airgun Expo
March 10 & 11, 2012
Placer County Fairgrounds
Roseville, CA (just NE of Sacramento on Hwy 80)
Contact Jon Brooks Don Reed (corrected 3/6/12)
Call 916-564-5225 (corrected 3/6/12)
LASSO big bore shoot
March 17, 2012
Terry Tate’s farm
Near Sulphur Springs, TX
This one isn’t well advertised.
Flag City Toys That Shoot
April 14, 2012
Lighthouse Banquet Facility
10055 S. R. 224 West
Findlay, OH 45840
Contact Dan Lerma, 419-422-9121 or firstname.lastname@example.org
NRA Annual Meetings
April 13-15, 2012
St. Louis, MO
This is like a mini SHOT Show that’s open to the public. It has a 10-meter airgun range (run by Pyramyd Air) for shooting manufacturer-supplied airguns (there’s a charge for shooting). Free to NRA members, $10 for non-members. Click for website. Pyramyd Air is giving away free tickets to the show. If you’re not an NRA member and want to get in for free, read the announcement on their facebook page and follow the directions.
April 27-28, 2012
Malvern, AR 72104-2005
Contact Seth Rowland, 501-276-1535 or email@example.com
Seth is still accepting table reservations, so contact him if you want to reserve a sales or display table.
Okay, on to today’s report.
I didn’t think this day would come so soon, but I’m going to show you what happens when you shoot the FWB 300S at 50 yards. Or more correctly…when I shoot it! I say that because 50 yards is a distance at which all false pretense of accuracy falls away. Fifty yards is a harsh challenge for a 650 f.p.s. air rifle like the 300S. All the wonder of those tiny groups at 10 meters becomes doubt that you can even shoot this far when the range stretches out more than four times as far.
I needed a windless day and as luck would have it, I got one. Or at least one where what little breeze there was could easily be managed. When I got set up to shoot, it was about 8:15 a.m., and the breeze was running from still to an occasional puff of about 1 m.p.h.
I used the sandbag rather than the rifle rest because I already knew the 300S did well on it. I first fired about four rounds to warm the action and to “awaken” the mechanical parts. I’ll talk a lot more about that in a PCP primer I’m writing, but even spring-piston guns have to wake up if they’ve sat for more than a couple hours.
I’m shooting the JSB Exact RS pellet for this test. We all agreed that to test the gun with wadcutters at this range would be unfair, because wadcutters are known to be inaccurate after about 25 yards. And the RS pellets proved to be the most accurate domed pellets in the accuracy test I did.
For targets, I wanted to use the 50-foot timed and rapid-fire pistol targets that I always use at 50 yards. The bull measures just larger than 3 inches, which is a good size for most peep sights at 50 yards. I like these targets also because they measure 10.5″x12″, which gives a lot of room for the pellets to miss the mark and still be seen. I knew the pellets would drop when going 50 yards, and I’d planned to stack two targets — one above the other, so I could aim at the top bull and possibly hit somewhere on the target below. But I only had two of these targets! I’d failed to pack enough of the right kind of targets in the range box. Though I had plenty of targets, only two were what I wanted.
No problem, I thought. Years ago, I figured if this ever happened I would use 10-meter pistol targets instead of these larger targets. They’re on smaller paper, but I could still place one above each larger target to use as an aim point. Ten-meter pistol targets have a bull that measures 2.35 inches across. It looks similar to the larger bulls when you look at them casually, but at 50 yards the difference through the sights is noticeable. They’re too small in the front aperture, which leads to possible aiming errors. I could see that on the first group I fired and also when I examined the group afterwards.
As I predicted, the group dropped about eight inches at 50 yards, so the group was printed on the target below the one I aimed at. I knew that the smaller bull was too small to work well at this distance. But there was another way of doing this.
I still had two of the 50-foot timed and rapid-fire targets stapled to the target backer; and underneath everything, I’d stapled a 2′x4′ sheet of plain target paper. It’s the back of a silhouette target that I always use when I’m unsure of where my bullets or pellets will go. The plain light paper allows me to see the holes even though they don’t strike the intended target. Because it’s so large, it covers the entire target backer; so, unless the rifle is really out of whack, I’ll see where the pellets are going.
Then, I proceeded to shoot another 10-shot group of unsorted pellets at the larger bull on the left, knowing that they would strike the plain target paper below this target. They landed about two inches below the target and gave me a perfect group of 10 on the plain paper.
This time, the bull was filling the front aperture as it should, so the group was much better. It measures 1.689 inches between centers. Remember, this is a 10-shot group. It’s about 40 percent larger than a 5-shot group fired under similar conditions. That doesn’t mean that it’s exactly 40 percent larger; and, yes, it’s possible for the first 5 shots to land the farthest apart, so that a 10-shot group doesn’t grow any larger. But the probability that you’ll do that is very low. If you keep on shooting after 5 shots, it’s more likely that your group will continue to enlarge until it’s, perhaps, 40 percent larger after 10 shots than it was after the first 5.
Some notes on sorting the pellets
I had sorted the JSB pellets the evening before going to the range. Because JSB pellets are so accurate, I thought they’d also be very uniform, but they weren’t. To get 20 pellets that all weighed 7.30 grains, I had to sort through almost 40 pellets! The weight ranged from 7.10 grains to 7.40 grains. While that isn’t as large a spread as other pellets, it was still a surprise. I thought I might find two or three pellets that didn’t weigh the same, but it was worse than that.
By this time it was around 9 o’clock, and the breeze was picking up. I had to wait for breezes of 3 m.p.h. to die before shooting. When they did die, though, the air was perfectly still again. This time, 10 pellets that were sorted by weight grouped in 1.383 inches. That isn’t much better than the unsorted pellets, and it was not the result I’d expected.
Ten-shot group of weight-sorted pellets at 50 yards made this 1.383-inch group. Not much improvement over the unsorted pellets! You can see a very small 5-shot group at the left of the larger group. That group measures 0.577 inches between centers, but I can’t say that it indicates anything.
This test didn’t turn out as I’d expected. Either the weight of the pellets doesn’t matter that much, or something else was happening to skew the results. I think I may know what that something is. It was apparent as I shot that I was unable to detect any slight canting of the rifle. There’s no bubble level on this rifle. And look at all three targets. They’re all wider than they are tall, which is a giveaway that I was canting the rifle randomly. In fact, this is such a telling result that I believe I have to rerun this test, just to eliminate the cant!
I’ve conducted a host of special cant tests in the past to learn about the effects of canting the rifle; plus, when I shoot my Ballard rifle — which has a bubble level attached to the front sight, it’s always difficult to center the bubble because it’s so sensitive. So, canting is a known problem with which I have some experience.
By the time I completed the group of weight-sorted pellets, the breeze had picked up and the day of testing this pellet rifle at 50 yards was over. But like I said, I’m not satisfied with these results and will have to run the test again. Next time, I’ll mount a scope, just for the additional precision it will give, plus it’s lot easier to use a bubble level with a scope than with a peep sight.
by B.B. Pelletier
I’m writing this report because I saw from the comments on the accuracy versus velocity test that several readers do not know what a scope level does. And where three people speak out, there are three hundred who are reading and remaining silent.
They say that there’s nothing more zealous than a convert, and I expect that is true of me when it comes to scope levels. I have understood their need for a long time and even conducted a fairly extensive cant test back in my Airgun Letter days, but it was my .38-55 Ballard single-shot rifle that really drove the message home. That rifle came with a bubble level, and it’s far more precise than the levels we find on air rifles today. The bubble moves very slowly, making it important to check the level just before you begin the squeeze; because what looks like a level gun one moment can change slowly to a canted gun if you don’t watch the level. By contrast, the scope levels I’m using with airguns have bubbles that move very fast, are much easier to see and are far simpler to work with.
Today, I want to demonstrate the effects of using a bubble level. I’ll use the same Whiscombe JW75 that I’ve been using for the velocity versus accuracy test, because we already know it has an accurate pellet in the Beeman Kodiak. For this test, I first seasoned the bore with six shots, then fired a group of pellets with the bubble deliberately off-center in both directions. I fired a second group where I paid no attention to the level and just tried to level the rifle as best I could through the scope. The final group was shot using the level with the gun absolutely level for each shot. The distance was 25 yards, which several readers mentioned is almost too close to see the effects of using a level.
This is the insidious part of leveling a gun, and it’s what I’m showing with today’s test. You really can’t see a pattern to the group from not leveling the gun when you’re shooting as close as 25 yards, but you can see that there’s a difference between a level gun and one that’s not level. We’ll get to that in a moment.
What the level does
The scope is mounted above the barrel, so it’s adjusted to look through the trajectory of the pellet so that the point of impact coincides with the aim point at a certain distance from the gun. However, if you tip the gun to either side and then sight it, your crosshairs will still be on the point of aim, but the barrel will no longer be directly below the scope. It will be to one side or the other, depending on which way the rifle leans.
Our intrepid blog reader duskwight was kind enough to give us a link to a superb animation of this phenomenon. You will find it here. Someone (Wulfraed?) said that a gun will describe an arced impact point if the cant is shifted through an arc, left to right. That’s exactly what the online animation shows, and it’s exactly what a scope level does for you.
One reader asked if the scope level would still make a difference if the scope had been optically centered. Yes, it would. There’s no relationship between optically centering a scope and using a scope level. The former simply allows you to adjust the elevation for different ranges without the shot group moving from side to side because the scope stays centered all the time, while the latter relates to how the scope and rifle are actually held when fired. The first is optical, and the second is physical.
The test is straightforward. First, I seasoned the bore with several shots. Then, I fired a group of 10 shots at 25 yards with the rifle canted to the right for 5 shots and to the left for 5 shots. The cant was controlled by the position of the bubble in the level, and I stopped tilting the rifle the moment the bubble came to the end of its travel. Obviously, there’s some error in this, as the bubble level is not a precision instrument, but I think you’ll get the idea.
And here’s the group. Do you see that you cannot tell that the rifle has been purposely canted in two different directions? This just looks like a large group for a Whiscombe at 25 yards. Group measures 0.905 inches between centers.
Next, I shot another group of 10, only this time I completely disregarded the level. I just shot and tried to hold the gun level from the visual cues seen through the scope. This is the same way I shot the rifle during the initial accuracy test.
For this group of ten Kodiaks I disregarded the level. I tried to keep the rifle level by visual cues through the scope, but that was all. Group measures 0.874 inches between centers — or not much better than when I was purposely canting the rifle in two different directions. Also note how much like the first group this one looks.
For the last group I leveled the rifle for each shot. I was also careful to hold the rifle exactly like I was holding it for the other two groups. The results are very telling.
This group of 10 Kodiaks was shot with the rifle leveled each time. It measured 0.624 inches across the centers; however, if the stray ninth shot is omitted, it would measure 0.36 inches. If you check the last accuracy test I did with Kodiaks on Friday, you’ll see that this result is very close.
I’ve seen this same test result repeated numerous times over the years, so I don’t feel the need to run multiple groups and do a sample of each type, but you’re free to do so. I know this is what happens when a scope level is used, which is why I used one when I competed in field target.
You might ask why I don’t always use a level when testing airguns. The short answer: time. It takes a lot longer to settle down and check everything when you shoot this way, and I don’t think it’s always necessary, anymore than I would use a minute-of-angle rifle in a firefight. An AR 15/M16 is fine for that kind of work. But when real accuracy is on the line, a level brings out the very best a rifle has to offer.