Posts Tagged ‘air transfer port’
by B.B. Pelletier
Dammion Howard (left) shows off some new airguns he found under the tree this year!
Happy New Year from Tom & Edith!
One nice thing about watching a TV program is that it only takes an hour or less to view. You have no sense of the man-weeks of work that go into a short production on screen. Sometimes, the same thing happens in the world of airgun blogs.
I won’t say I’ve been dreading today’s report; but from past experience adjusting the HOTS on the Whiscombe rifle, I knew it might take longer than anyone could imagine to get a good result. It’s easy to say, “Adjust the HOTS for optimum performance with a certain pellet.” Actually doing it is where you discover if it’ll be easy or hard. The report I have for you today was very hard.
I allotted several hours to the actual testing and adjusting that would have to be done. And with my past experience with the Whiscombe, I knew shortcuts the average shooter wouldn’t think of. Let me lay the groundwork so you understand what’s happening in this process
The Whiscombe harmonic optimized tuning system (HOTS) consists of a weight that can be adjusted in or out along the axis of the bore. A jacket around the barrel is threaded to receive this weight. The threads on the weight are very fine, and one turn of the weight moves it a millimeter in either direction. One complete turn of the weight constitutes 1mm movement of the weight.
Besides the weight, there are two other metal parts. One is a short collar that locks the weight in position after it’s been adjusted, and the other is a much longer cover that encloses the entire HOTS from sight. This longer cap doesn’t need to be removed from the weight to make adjustments, just provide access room for the special wrench that moves the weight.
Here you see the HOTS mechanism. The threaded weight is turned in or out of the barrel jacket by the wrench. Once the weight is where you want it, lock it down with the knurled collar on the barrel jacket. Then, install the long cap, and the job is done.
Where to start?
The problem is always the same: Where do you start adjusting the weight? The simplest way is to start right where you are — with the HOTS in the last position it was set. Shoot a group at that setting and go from there. I had that data, of course, from the earlier part of this test, so that’s where I began. Because the last transfer port is still installed in the rifle, the Beeman Devastator pellet still develops about 772 f.p.s.
When I shot a group at this velocity in the earlier test, 10 shots went into a group measuring 1.073 inches between centers. I was looking for a group somewhere near that size this time, too. It might be a little smaller or larger; but if it was a quarter-inch group, there was a problem with the results of the last test. The same care was taken with each shot; to do any less would have skewed the results or made them unreliable at the very least.
The first group shot in this test, shot with the same HOTS setting, measured 0.953 inches between centers. That’s 0.12 inches smaller than the group from the last test. I would call that in the same ballpark and therefore a confirmation that the last test was sound.
Adjusting the HOTS
Whiscombe says that there will be several sweet spots throughout a one-inch movement of the weight, which is approximately 25 full turns. He also says that one spot will be better than the others, and that’s the one to look for. He just doesn’t tell you how to find it, other than by adjusting the weight one turn at a time. But my experience told me that the sweet spot was probably not where the weight was at this time, so I turned it in (toward the receiver of the gun) four full turns and shot a second group. This is where my experience with the Whiscombe was supposed to pay off.
I wasn’t going to waste my time shooting 10 shots if the first 5 were spread out. Why bother? I wanted a tight group, and if inside 3-4 shots — or even 2, on one occasion — there was already a large separation, it was no use going further. I turned the weight in 4 full turns and shot another group. This group teased me with the first 5 shots in less than a quarter-inch, but the final 5 expanded that to 0.977 inches. Can’t be certain because of measurement errors, but no improvement at all.
Next, I tried the weight 5 turns in from the start point. The group was worse. I backed out to 3 turns in and got about the same size group as with 4 turns in.
At this point, I experimented with some subtle adjustments on a half and then a quarter turn. At 3.5 turns in, I got a group that was slightly smaller than the one at 4 turns, but it had one called flyer. I tried another quarter turn in and got 4 shots in a group measuring 0.998 inches between centers. Obviously, I wasn’t going the right way.
Okay, this wasn’t working. I adjusted the weight out in the other direction 9 full turns past the initial setting and shot another group of 10. This time there was some success, as the group measured 0.794 inches between centers. I wanted to call that the end of the test; but looking at the group, I knew it wasn’t enough of a difference to impress anyone. Even though it does show improvement over the baseline group, I would like to show a larger change since one of the Devastator groups in the earlier tests measured 0.616 inches. This group was too much larger than that. The gun should be able to do better if harmonics and not velocity was the main driving force behind accuracy.
By this time, I’d fired 49 shots in about 90 minutes. The test work had lasted much longer than expected, and I had to quit for the day.
A happy accident
The next morning, I was back at the bench and trying to complete the work. I figured I would adjust the weight out from the initial setting by a certain amount but as I tried to do that a happy accident happened. The front cover got stuck together with the weight; and by the time I noticed it, I’d already adjusted it 15-20 turns. Except, I had no way of knowing how many turns it was. I had to start all over, and this time from a random place that bore no known relation to the initial start point. Not that it mattered, except I didn’t want to waste all of the work from the day before.
I adjusted the weight at a point that looked to be well away from the initial setting. Then, I shot a group as a baseline. Or I should say I began to shoot a group. After 3 shots, I had a spread of 1.153 inches between centers — the largest spread of the entire test to this point. No sense finishing that one!
Past experience has shown that the sweet spots are often a couple turns in either direction. I guessed and turned the weight back in three turns from the starting point. And that was when it happened. The clouds rolled back, the angles sang and the rifle grouped like I knew it could. Ten shots went into 0.523 inches. That’s not only the best group of this little experiment with the HOTS, it also beats every group fired with the rifle during the main test conducted earlier.
With this kind of data in hand, I can say with some confidence that harmonics and not velocity is the main driver in how accurate a spring gun can be. I say this because the worst group shot during the velocity test was adjusted harmonically into the best group of the test with this pellet. There’s no chance in this group — it’s clearly much better than it was in the beginning.
Could the rifle shoot this pellet even better? Maybe. But it isn’t necessary to prove the point we were trying to prove.
Next, I want to adjust the rifle for Beeman Kodiaks at a higher velocity and test pellets straight from the tin against pellets that are sorted by weight. Today’s report should give everyone the confidence that, if a difference in accuracy is noted, it will be because of the pellets and not the gun.
by B.B. Pelletier
Kevin Currie is shown shooting a tuned .177 Gamo CFX with his son and dog. He says his CFX is scary accurate!
For those who celebrate Christmas, Merry Christmas from Edith and me! This is our last opportunity to wish you a Merry Christmas before Sunday, but I would like to hear on Monday from anyone who received an airgun, airgun-related gift or a firearm for Christmas. I’ll tell you what I got, too.
Today, we’ll look at the results of this test to see if there’s a direct inverse relationship between pellet velocity and accuracy. I’ll start with the results by pellet and see where that goes.
A word about the shooting technique
The first accuracy test I did was in Part 2 of this report. I found fault with that test, though, because of how I was shooting. I wasn’t using the scope level on the gun all the time, and I also wasn’t “seasoning” the bore by shooting several shots before starting a group. Some pellets seemed to need the seasoning, while with others it didn’t seem to matter as much. I reshot the entire first accuracy test and seasoned the bore for every pellet, plus I paid attention to the scope level.
The need for seasoning seemed to go away as testing progressed, but the scope level was always consulted for every shot. I know that the level improved the performance of every pellet that was shot. The jury is still out on the seasoning issue.
All the accuracy results seen here are not from the first time I shot the rifle, but the second. All were shot at the velocities indicated. Just the shooting techniques were adjusted as indicated.
In this test, the 7.1-grain Beeman Devastator was the “little pellet that could.” From the start, when it was averaging 1,216 f.p.s., this lightweight hunting pellet produced 10-shot groups under three-quarters of an inch at 25 yards. That went against the popular belief that supersonic velocities are harmful to accuracy.
The Devastator turned in the following performance at 25 yards.
Velocity (f.p.s.)….Group size
Okay, you don’t need a graph to see a problem here! This pellet is obviously way more accurate at 1,123 f.p.s. than it is at 772 f.p.s. Theory says that shouldn’t be because the first velocity is breaking the sound barrier, which is where all the accuracy gremlins are supposed to live.
Looking at the group size in relation to the velocity, it appears that 1,123 f.p.s. is the most accurate velocity for this pellet in this gun. That would entirely negate the theory that velocity destroys accuracy. So, if there is such a relationship, it must be subordinate to and less influential than some other influence. I think that other influence might be vibration, but that’s just a guess.
Crosman Premier lites
The 7.9-grain Crosman Premier lite was the next pellet I tested. Here are the results of all four tests at 25 yards.
Velocity (f.p.s.)…Group size
The Premiers did give a linear relationship between velocity and group size, though the two groups from the middle two velocities are so close in size that they could be the same. Measuring error is greater than the difference between these two groups.
The group at the lowest velocity is obviously the best of the four and by a wide margin. The data from this pellet isn’t clear as to what is causing the accuracy improvement. It could be either velocity or vibration. However, at 915 f.p.s., the pellet is going slow enough to be out of the transonic region, while at 1,057 f.p.s. it isn’t. I would have expected to see an accuracy gain at that lower velocity that’s greater than what we see here if the real problem is just velocity.
Next, I shot the heavyweight Beeman Kodiak pellet. It proved to be the most accurate pellet of this test and the only one that turned in a group smaller than a half inch. Please bear in mind that these are all 10-shot groups and are about 60 percent larger than they would be if they were only five shots. I didn’t shoot 10 shots for that reason — but because, in doing so, I reduced the probability error significantly. In short, I can trust that the group sizes shown are closer to reality that if I had shot two 5-shot groups and averaged them.
Kodiaks shot tight right from the start, even though the first group of pellets was actually close to or just within the transonic range. Since I didn’t keep atmospheric data for each day I shot, I can’t say where the sound barrier was exactly; and the transonic region, which is 0.8 mach to 1.5 mach, is calculated based on that. In practical terms, I know that 992 f.p.s. is pretty darn close to transonic, because the sound barrier can be anywhere from 1,050 f.p.s. to 1,125 f.p.s. depending on the temperature and humidity where I shoot.
Velocity (f.p.s.)…Group size
However, the groups don’t seem to support the velocity/accuracy relationship very well. It’s true that the first and second groups are too close to really say which is larger than the other, but the velocities at which they were shot are very important. One borders on the transonic, while the other is probably slower than transonic.
But look at that third group! When the velocity averages 819 f.p.s., the Kodiak loves this rifle! Is that a velocity thing or is that influenced by the harmonics of the rifle at that power level? I’m inclined to think that it’s the latter, though we do not have enough data to prove it.
The last group is the worst, though the velocity is getting pretty low for a pellet this long and heavy. We don’t know much from these results, either. But if it does turn out to be harmonics over velocity, then this pellet is probably the best one for the rifle, and the Harmonic Optimized Tuning System (HOTS) needs to be adjusted for it at around 900 f.p.s.
The 16.1-grain Eun Jin pellet is too heavy for the power potential of this air rifle. Although the Whiscombe JW 75 is a 30 foot-pound air rifle — that’s only in .25 caliber — when the heaviest pellets are used. In .177, it’s much closer to 20 foot-pounds and is, therefore, too weak to drive the 16.1-grain .177 Eun Jin fast enough for accuracy.
Velocity (f.p.s.)…Group size
Starting with the second group, I could tell that the Eun Jins weren’t going to do well. Like the Kodiaks, they’re also too long and heavy to make any conclusions regarding velocity versus harmonics. They just don’t give enough speed in this rifle to properly examine the velocity question.
A different look at the data
The “sweet spot” was different for every pellet. Each pellet had one velocity at which it grouped the best; disregarding the actual velocity, it went like this:
Fastest was best—>Eun Jin
Second fastest was best—>Devastator
Third fastest was best—>Kodiak
Slowest was best—>Premier lite
That, by itself, is a pretty good indicator that supersonic speed isn’t a problem, since the Devastator was supersonic when it produced its best group. One thing you cannot do is compare the group sizes…one to another…between the pellets. Let each pellet stand alone because there are far too many variables to make a cross comparison like that.
Was the Whiscombe a valid testbed?
Some thought the Whiscombe was the wrong gun to use because it’s so inherently accurate. I disagree. I think its accuracy makes the results all the more valid. Besides, controlling many of the magnum breakbarrel springers is too difficult and gets in the way of testing. They require perfect hold technique for every shot. The Whiscombe is much easier to control, which takes that variable out of the equation.
Some felt that only a pneumatic should be used since harmonics seemed to be causing accuracy errors. Well…that was the point of testing! Now we know a little more about how the pellets respond to supersonic speed, and it seems to me that it doesn’t matter as much as many, including me, have believed. People don’t just shoot PCPs. I do plan on testing this same sort of thing with a PCP whose velocity I can control over a wide range, and those results will also be interesting — but they don’t negate the value of testing a springer.
I used the Whiscombe for this test because, even when I altered the velocity, the harmonics of the gun remained the same. The powerplant always ran at full power, regardless of how fast it shot. And the barrel was always the same, too. The only thing that changed was the velocity.
What comes next?
I’m sure some of you will have additional interpretations to make about this test, and now is the time to make them known. My next step is to use the rifle as it is currently set up and adjust the HOTS to see what I can do to the size of the Beeman Devastator group. I’m thinking the HOTS can be adjusted to shrink it significantly. I have a procedure in mind to cut the time it takes to adjust the rifle because this can take hours if you aren’t careful! I’ll share that procedure with you in that report.
If I’m right about being able to tune the HOTS to get a small group at the average of 772 f.p.s., then the next thing I’ll do is shoot another group with the bubble level taped to hide the bubble. I won’t intentionally try to enlarge the group, but I just won’t be able to consult the bubble for every shot. That will result in another group that can be compared with the best group I’m able to shoot when the HOTS is tuned, because it will still be tuned for that group.
Finally, perhaps one additional test is needed. I’ll set the rifle to shoot Kodiaks in the high 800 f.p.s. range and adjust the HOTS for the best accuracy. When I get the best group, I’ll shoot one group of weight-sorted pellets against another group of pellets selected straight from the tin.
When all of this is completed, I should be able to state what I think are the most important components of accuracy. You’ll be able to see how much difference these things really have on group size. Most of you can’t adjust the harmonics of your spring guns, so you need to find the one pellet that shoots the best. Perhaps it’s time someone made a generic harmonic tuner for springers, again.
by B.B. Pelletier
Joel’s winning photo is of his niece, Paysen. He was teaching her to shoot a Crosman 66 over Thanksgiving weekend.
Today, we’ll complete the testing of the four pellets at four different velocities in the Whiscombe rifle. The premise of this test has been to explore the effects of velocity on accuracy by shooting the same pellets in the same pellet rifle at four differing velocities. I will make today’s report and comment on how the test went, but this will not be the final installment of this test. There will be at least one more summary report that puts all the data into perspective. And if there are side issues to explore, maybe there will be more reports.
At this point, I think I know what I’m going to find when I look at all the data, but there have certainly been a few surprises in this test. And the surprises continue in today’s report. Let’s get right to it.
This time, the Beeman Devastators were averaging 772 f.p.s. Since this is a very lightweight lead pellet, at just 7.1 grains, I would have thought this velocity would be about as ideal as it gets. The pellets thought otherwise. Ten shots went into a 25-yard group that measured 1.073 inches between centers. You’ll have no problem counting all 10 shots, because none of them seemed to want to go to the same place.
However, I do want to draw your attention to the upper right portion of the group. There are 5 holes in a much smaller group measuring 0.399 inches. This is what the best 5 out of 10 shots looks like, and it’s a temptation to say that this is what the rifle/pellet can do. Think not? Well, in a national magazine, a popular gun writer who traditionally shows three-shot groups when talking about accuracy, recently published an article about .22 rimfires in which all the groups were 5 shots — very uncharacteristic for him. But when he reported the group sizes, he twice mentioned the size of 4 out of the 5 shots in those groups! In other words, he couldn’t resist the temptation to make the gun sound better than it really was — even when the evidence was right out in the open. That’s why I most often shoot 10-shot groups.
Beeman Devastators did not stay together this time. This group measures 1.073 inches between the two farthest centers. But look at the much smaller group of 5 in the right-hand corner. They’re both legitimate and a fraud at the same time. They were legitimately shot by the rifle in this test, yet they do not represent the true accuracy of the rifle at 25 yards at this velocity.
Crosman Premier lites
Next, I shot a group of Crosman Premier lites. They did just the opposite of the Devastators — grouping the best they did out of all four tests. The group measures 0.593 inches between centers. That says a lot for this pellet, but perhaps not everything. The velocity at which they traveled was an average of 732 f.p.s. Is it the velocity or something else that makes them so accurate? We shall just have to wait and see.
All shooting was done with care
Lest you think I relaxed at any time during this test, I assure you I did not. Each shot was fired with the same care as all the others. The bubble level was consulted each time just before the shot was taken. I now have the trigger breaking at less than 8 oz., so it’s perfection. I’ve even concentrated on my hold to make it as much the same from shot-to-shot as I possibly could.
Next up were the Beeman Kodiaks. These were the pellets that had proved to be the most accurate up to this point in the test. This time, however, they opened up to 0.864 inches between centers. You can see that 8 of the 10 shots are in a much tighter group, but let’s not go there yet. The group you see represents how well these pellets did at an average velocity of 658 f.p.s.
We have long since passed the point at which the 16.1-grain Eun Jin super-heavyweight pellets are accurate; but just as the United Nations continues to grant its chairmanship to members of the smallest third-world countries, so we continue to shoot this pellet with each test — pretending that is has some part to play. Last time, Eun Jins printed some two-plus inches below the aim point. This time, with the velocity averaging 501 f.p.s., they dropped 6-3/8 inches! They were so low that I had to reorient a target to see them print on the paper.
The group measured 1.724 inches between centers. That’s larger than last time.
Like I said in the beginning, I’ll look at today’s results right now, but there will be another report dedicated to the entire test. I want to know what you readers think about this, because a lot of what I do ultimately comes from you.
What I see in today’s results sort of implies that accuracy falls off at lower velocities. Now, I don’t happen to believe that’s the case; but except for the Premier lites, that’s exactly what happened today. That suggests that something else is causing the larger groups. Perhaps vibration? Maybe that needs to be explored.
Looking at the Beeman Kodiak group, and to a lesser extent the Premier lite group, it seems like pellet selection might improve these two groups significantly. I shot all the pellets exactly the way they came from the tin or box. No special sorting technique was used. Would accuracy have improved if I had weighed these pellets and examined them critically before shooting? That’s a question so intriguing that I’m almost compelled to test it next.
On the other hand, no weighing or sorting will improve the groups made by the Beeman Devastators or the Eun Jins that much. They’re just what they are, as the openness of their groups suggest.
If I didn’t have a lot of experience shooting pellets at lower velocities, I might be tempted to make up some sort of explanation as to why they did so poorly. But I’ve shot other slower air rifles that exhibited excellent groups at 25 yards, so it seems like it must be something else. That’s where the thought of vibration comes in. With the Whiscombe, I can alter the vibration nodes with the Harmonic Optizmized Tuning System (HOTS).
That makes me think of something else. You know how we always say that to find the best pellet for a given gun you have to try them all? Maybe what you’re doing is finding the pellet that responds best to the way the airgun vibrates!
You tell me what you think I should do next. I won’t promise to do it all, but I will read with great interest what you have to say.
by B.B. Pelletier
Aaron’s winning photo. He’s holding a GSG 92 CO2 BB pistol made by an airsoft manufacturer that now also produces realistic lookalike airguns.
This is an exploration into the theory that high velocity reduces pellet accuracy when it reaches and exceeds the transonic speed region, or about Mach 0.8 to 1.2. We have thus far examined four different .177 pellets at three different speed levels, produced by shooting them in a Whiscombe JW75 spring rifle. Because all pellets have been fired in the same barrel and powered by the same powerplant, the conditions have remained the same, except for their velocities. That was altered by the use of air transfer ports of varying sizes, that passed the compressed air at differing rates.
In this fourth test, I’ll reduce the velocity of the four pellets even more, to as low as I am able to go with this rifle. Then, we’ll have four sets of groups to examine for each of the four pellets. While that isn’t enough testing to prove anything conclusively, it should provide a good indicator of what happens when pellets are both within and outside of the transonic velocity range. The current theory says that pellets are not designed for transonic or supersonic flight and will be less accurate at those speeds than they will at speeds that are less than transonic.
I’ll record the velocities of all four pellets today and then shoot them for accuracy in the next report. We’ll have at least one additional report in which all the results are compared and, to the extent possible, analyzed.
Pause to reflect
Before I start today’s test, I’d like to take a moment to reflect. Although what I’m doing seems normal, but in 50 years it may seem quite exotic. By using a handmade air rifle like the Whiscombe, it’s as if I were shopping for a violin on the streets of Cremona in 1710 and was able to sample the works of Antonio Stradivari as they came fresh from the maker’s hand. Or perhaps more to the point, as though I were able to buy a target rifle with all the supporting equipment directly from Harry Pope. From the accounts I’ve read, shooters who were able to do just that back in Pope’s time revered his rifles as much as today’s airgunners revere a Whiscombe.
What will readers of the future think about our familiar association with an airgun that, by then, will have assumed an elevated cult status? Indeed, it’s almost in that position today. It’s also the perfect tool for conducting the very experiment I’m now reporting, because it can do everything we need while avoiding bias.
Some readers have suggested that just the fact that it’s a Whiscombe brings bias to the table. They say that because this rifle is so well made, it doesn’t necessarily represent most airguns and may be able to tolerate and even ignore the physical constraints we’re testing. I disagree.
The most accurate rifle in the world is still subject to the laws of the physical world. A bullet or pellet in free ballistic flight doesn’t know or care what sent it on its way. If that projectile is unstable for any reason, it’s going to behave just like a top spinning on a flat table. It’ll wobble and move in the direction in which its instability forces.
In fact, because the Whiscombe is so accurate it should be even easier to see those natural laws in action — if they actually work the way we think they do — because the gun doesn’t have all the extraneous “noise” that normally accompanies a spring-piston airgun. By “noise,” I’m referring to the extra vibrations that influence a rougher gun at the moment of, and just after, firing.
The transfer port limiter I installed for this test is the same one that was in the rifle when it was sent to me. So, we should see a large drop in the velocities of all four pellets. Accuracy testing should then prove very interesting.
The first pellet tested was the Beeman Devastator. They averaged just 772 f.p.s. with this transfer port limiter. The spread went from a low of 767 to a high of 779 f.p.s., so 12-foot-seconds from low to high. At the average velocity, they were generating 9.4 foot-pounds. That’s a velocity loss of 200 f.p.s. from the last test, which should do something to the group size.
Next, I tried Crosman Premier lites. This 7.9-grain domed pellet was pretty accurate pellet in the last two tests, but this time the velocity dropped to an average of 732 f.p.s. That’s about 185 f.p.s. slower than last time. It will be very interesting to see what effect, if any, that has on their accuracy. The spread went from 726 to 736 f.p.s. and the muzzle energy was also 9.4 foot-pounds.
Next up were the most accurate pellets thus far — the Beeman Kodiaks. These averaged 658 f.p.s., with a spread from 655 to 661 f.p.s. That’s an extremely tight 6 foot-second difference between the slowest and fastest pellet in the ten-shot string! And they generated 10 foot-pounds on the nose! That’s more than the two lighter pellets, which isn’t supposed to happen in a spring-piston gun. But it’s exactly what happened last time, as well, so there is consistency.
The final pellet I shot was the heavy 16.1-grain Eun Jin dome. This pellet is really too heavy for the powerplant, when it is set at this level, but we want to see what happens to all pellets on all power settings, so we have to test this one, too. They averaged 501 f.p.s. and ranged from 499 to 504 f.p.s., a five foot-second difference. They weren’t too accurate last time, and I expect them to get worse this time. The muzzle energy was 8.98 foot-pounds, which puts it last in terms of power. That remains the same as it has been throughout this test.
This sets us up for the next accuracy test, which should be most interesting, given the great velocity reductions we’re seeing. But I wonder if people will accept the results, knowing that they were obtained with a Whiscombe. As I said in the beginning of this report, all I think the Whiscombe does is give us a clear picture of the results. But we shall see.
by B.B. Pelletier
Before we begin today’s report, I want to reflect on a truth that helps explain why we’re sometimes dissatisfied with things when we get them. I was at the range last week testing some airguns, and I was using my Celestron 70C spotting scope, like I always do. This scope is good at 50 yards, but becomes marginal at 100 because it cannot resolve the smaller bullet holes. I don’t mean pellet holes, I mean .22-caliber bullet holes in the black bullseye at 100 yards.
A friend brought his Burris spotting scope to the range for me to compare, and the difference between the two was night and day. His scope was sharp enough to see small spiders walking on the target paper at 100 yards!
That same day, I shot a couple rifles my other friends had brought to the range. One of them was a fantastically accurate custom 6mm/.22 that can shoot a half-inch, 5-shot group at 100 yards. But it’s scoped with a BSA 4-24X scope that isn’t available at Pyramyd Air for good reason. It’s so dark and muddy that I couldn’t see the bullet holes as I shot this very accurate rifle. And I was shooting at a bright orange dot on white paper! I couldn’t see bullet holes on that! The scope was set at 16X because anything above that caused the image to go white from flare, and we were shooting in total shadow under a covered roof!
Another friend had a Lyman Super Targetspot scope that was 10X, and I could easily see all the holes his .220 Swift was making at 100 yards on the same kind of targets. So with six fewer magnifications, I was able to see the holes because of the superior optics. The Lyman scope is no longer made and a good used one will fetch about $800, while you can probably buy the BSA for under $200 all day long.
Back to the spotting scopes
My Celestron spotting scope has 30X, 60X and 90X power available. Where do I have it set? Between 30X and 60X, which is about 45X. Because anything greater than that muddies up the image too much — even at 50 yards. My friend’s Burris spotting scope only goes up to 45X maximum, yet it’s many times clearer than my Celestron. And I found on this day that only 10X was actually required to see .22-caliber holes at 100 yards on a light target. A black bull is probably harder to see with just ten power, but with 45 power it is easy!
So, I went home and researched that Burris spotting scope. It sells for about $175 at Midway, where the Celestron C70 Matsukov I have sells for about $80. But what good is it if it doesn’t do its primary job?
That got me thinking about shooters who purchase air rifles on the basis of velocity, alone, without appreciating all the other variables that come in the package. Things like smoothness, a good trigger and, most importantly, accuracy are pushed aside for velocity and low price.
I rant on about these things because they are also among my personal flaws. I’ve always tried to buy the cheapest of everything, and often the “mostest powerfulest,” too. So, I’m constantly drawn back to them whenever I find that I have made another dumb blunder.
On to today’s report
This was a day of great learning. When I summarize this series of tests, today will mark a big turning point, I believe. I learned a lot of things — all of which I will now show you.
As always the first pellet tested was the lightweight Beeman Devastator. I’ve been amazed at the performance of this pellet from the start of this test, and last time I predicted that it would shoot even smaller groups this time.
Sorry, but that didn’t happen. The first four shots seemed to confirm the need to “season” the bore before shooting each new pellet. I’m showing that target here so you can see what I saw.
This sight-in target for Beeman Devastators fooled me. Shot one was the upper right. Shots two and three were in the same hole on the left and shot four was between that group and the first shot. At the time, I felt this was demonstrating the need to “season” the bore before shooting a group with this pellet.
Shot one was the on at the high right, then the tight group of shots at the left were the next seven shots. Just when I was about to proclaim a universal law of bore seasoning had been discovered, shots nine and ten fell between the first shot and the group at the left.
Now, I was in a quandary. If the last two shots had strayed from the group in the same direction as the first shot, what was it telling me? Maybe the bore didn’t need seasoning. Maybe the Devastator just doesn’t like this velocity. Only another group would tell me for sure.
I believe that this particular velocity is one the Devastator pellet doesn’t like. As you know, I haven’t touched the Harmonic Optimized Tuning System (HOTS) on the barrel of my Whiscombe during this test. And I won’t. I don’t really care how accurate the gun is with a certain pellet. I was trying to see if there is a linear relationship between velocity and accuracy, and these two groups suggest that there isn’t. You’ll have to read the rest of this report to fully understand what I mean.
Crosman Premier lites
Next, I shot 10 Crosman Premier lites at 25 yards. This time, the target was very good, but the point of impact moved about a half-inch higher than last time. I was prepared to shoot four shots to season the bore, but the pellets kept going through the same hole, more or less, so I just completed the group without any seasoning.
This is a nice group of 10 Crosman Premier 7.9-grain pellets at 25 yards. It measures 0.747 inches and is actually slightly larger than the smallest group of Devastators. It’s almost identical to the last group shot during the previous test, so no big change in group size with this pellet.
The change of impact point was another big lesson this time. I’d seen it earlier, but not as dramatically as this time. The overall size of the group remained the same as before. That’s another indication that this is a barrel vibration issue and not one that’s driven by a change in velocity.
The next pellets I tested were the Beeman Kodiaks, which have performed so well to this point. This time, the point of impact shifted up about three-quarters of an inch, but the group remained very tight. This time, 10 shots went into a group measuring 0.472 inches at 25 yards, which I believe is currently the best group of this entire test. Last time, they gave us a group measuring 0.628 inches.
And, now, it’s time to report the performance of the super-heavyweight 16.1-grain Eun Jin pellet. Last time, they made the worst showing and that continued into this test, as well. What was different was the fact that the point of impact dropped more than two inches with what was just a slight reduction in velocity.
I was aiming at the center of the bull above, where they impacted! This was a dramatic change of impact point from the last test. Group size for these 10 Eun Jin pellets was 1.27 inches between centers. That’s a little larger than last time, but the change of impact was far more noticeable.
What have we learned?
Well, nothing has been linear in this series of tests — the way I expected. But what the vibrations are doing seems pretty obvious. So, the next test is both needed, as well as anticipated.
by B.B. Pelletier
For the benefit of readers who have landed on this article first, this is the sixth test in a series of reports designed to test how velocity affects accuracy. I’m using a Whiscombe JW75 breakbarrel/underlever rifle with a .177-caliber barrel installed. That way the same powerplant is being used for each test. I’m controlling the power of the gun by the use of different air transfer port limiter screws that allow less and less air to past through.
The Whiscombe rifle uses dual opposed pistons that come together to compress the air when the gun is fired. The rifle has no recoil and just a minor impulse that can be felt — yet it’s one of the most powerful spring-piston air rifles ever made. My rifle can produce over 30 foot-pounds in .25 caliber.
Four pellets were chosen at the start of this test and have been used in each velocity and accuracy test that’s been conducted. Two of them were supersonic in the first test and one remained supersonic in test two, while the other was still in the transonic region where wind buffeting occurs. It’s testing exactly what it was designed to.
Today, I installed a smaller transfer port limiter to slow down the four test pellets even more. This was the first time all four pellets were safely below the sound barrier, and the shooting was uniformly quiet. You probably should read the first five reports at the links provided above to understand all that’s happening.
This 7.1-grain lead hollowpoint hunting pellet has been the biggest surprise of this entire series. Normally, these types of special pellets are designed for maximum mushrooming and are not that accurate — at least not in my experience. But the Beeman Devastator has proven to be the exception. From the start, when it was leaving the muzzle at an average 1,216 f.p.s., it was accurate. So far, we’ve conducted only two accuracy tests, so the results of this one should prove interesting. As I said, this was the first time this pellet has left the muzzle at subsonic speed.
The average velocity was 973 f.p.s., with a low of 967 and a high of 977. That’s only a 10 foot-second difference between the slowest and fastest pellet, which I think is amazing. Usually, a pellet this light will also have a much larger total velocity spread over a 10-shot string. At the average velocity, this pellet is cranking out 14.93 foot-pounds of energy at the muzzle. That’s down from the initial 23.32 foot-pounds it was making when there was no transfer port limiter in the gun.
Can you guess what this pellet will do in the accuracy test? I think it’ll be even more accurate than in the past. But who knows?
Crosman Premier lites
Crosman Premier lites were next. Initially, they were leaving the muzzle at 1,134 f.p.s. when there was no transfer port limiter in the gun. Today, they averaged 915 f.p.s. and the spread went from 911 to 919, for a super-tight 8 foot-second difference. At the average velocity, these pellets were producing 14.69 foot-pounds at the muzzle.
Any guesses as to what this pellet will do in the accuracy test? The difference between the first and second accuracy tests was very small, but we’ve finally gotten the velocity down out of the transonic region, where all the buffeting is. They didn’t break the sound barrier the last time; but at an average 1,057 f.p.s., they were well into the transonic range. There could be a happy surprise from the Premiers.
Beeman Kodiaks averaged 819 f.p.s. with this transfer port limiter. The spread went from 817 to 824 for just a seven foot-second total variation across 10 shots. The muzzle energy was 15.2 foot-pounds. Notice that this heavy pellet is producing more energy than the two pellets that are lighter — something that’s not supposed to happen with a spring-opiston system.
I need to interject a word on Kodiaks. For some reason, their weights have varied widely over the past couple years. Where they had weighed 10.6 grains for several decades, someone decided to reduce the weight to 10.2 grains in 2010. Those are the pellets I have. But now I notice that the weight is back up to 10.4 grains. Obviously, someone is adjusting the weight of this pellet that was once considered one of the three most accurate .177 pellets on the market.
Kodiaks have been the most accurate pellets in both the previous accuracy tests (after I started using the scope level), but I don’t know if they’ll continue that trend at this new lower velocity.
Eun Jin domes
The 16.1-grain Eun Jin dome is really too heavy for the Whiscombe in its most powerful form. Certainly as the power is reduced, they become even less appropriate. In this test they averaged 618 f.p.s., and the spread went from 615 to 624, for an 11 foot-second total. At the average velocity, these super-heavyweights are producing 13.7 foot-pounds at the muzzle.
They produced the worst group last time, opening up from the group they had made with no transfer port limiter installed; and I predict this trend will continue in the next accuracy test. These are really best in powerful PCP guns — not in spring-piston guns.
Next, I’ll test the accuracy of these four pellets at 25 yards. I’ll use the same careful technique that I’ve been using so far to keep the results as free from bias as possible, so this should give us a good look at how velocity really affects accuracy — at least with these four pellets in this one gun.
You may not remember this, but at the beginning of this series I said that if the results of three velocity and accuracy tests seemed to warrant it, I could do a fourth test with the velocities cranked down very low. I’ll hold off on the decision to do that until I see the results of the next accuracy test.
Whether I do a fourth velocity/accuracy test or not, I’ll write a final summary report on all that’s been done in this test. If it seems worthwhile, I could do a second test using a Talon SS, so we can see the same relationship in a PCP gun. However, that hasn’t been decided, yet. We still have to get through this one.
by B.B. Pelletier
Today we look at the groups made by the four pellets used in this test at 25 yards when the velocity is diminished. Part 4 covered the velocity for each pellet, so go there to see where each one is.
If you like nice linear results, prepare to be disappointed. Today’s target do show changes, but they may not be in the direction you expect. Let’s get right to it.
First up were the 7.1-grain Beeman Devastator pellets. These pellets have been a real surprise in this test, because they have proven to be accurate at supersonic velocity and they are not sensitive to bore conditioning. Shoot one and it tends to go to the same place every time. They also do not show any first-shot tendencies that so many other pellets do. This is a real plus for hunters, who are always shooting the first shot. I will have to return to this pellet sometime soon and test it in other guns, because it seems to be a real winner.
This group measured 0.615-inches between centers, compared to the first group in Part 3 that measured 0.743-inches. Obviously the slower pellet is significantly better, but because we only have two groups to compare it is impossible to know whether one will always be better than the other. The Devastator is still going out the muzzle at supersonic speed, even though it has been slowed by about 70 f.p.s. This is the second-best pellet of this test, just as it was in the first test.
All the shooting conditions are exactly as reported in Part 3. The scope level was used for every shot and the rifle was held in the artillery hold, with the stock resting on my hand at the same place every time. So the same care is being taken each time I shoot, and that won’t change.
Next I tried the 7.9-grain Crosman Premier lites. The bore was conditioned with four shots before shooting the group shown here, and as before, the Premiers did show some wandering in the first three shots. After that, they seemed to settle down, though as you will see, settling is a relative term.
This time the group size remained nearly the same, at 0.754-inches. The group shot when the gun was shooting them faster measured 0.778-inches, which is too close to call. Yes, the group fired with the pellet going slower is a trifle smaller, but it is really too close to say there is a difference that’s due to the velocity — especially given the built-in error in measuring groups that I have talked about.
The third pellet I tried was the heavier Beeman Kodiak. They turned in the best group of the test, just as they did the first time. And the ten-shot group measured 0.628-inches between centers, which is very close to the 0.633-inches of the first test.
I cannot say that the Kodiaks did any better this time than they did in the first test. Even though the velocity was slowed by 55 f.p.s., it doesn’t seem to make much difference at 25 yards. Maybe that’s just not enough of a drop to matter.
The last pellet tested was the 16.1-grain Eun Jin dome. These pellets were never in the transonic region, even with no transfer port limiter in the gun. So this time they were just going slower. And what a difference that made!
Ten Eun Jin pellets were all over the place at 25 yards. They made this huge group that measures 1.118-inches between the centers of the two pellets farthest apart. This is the worst group of this test and also much worse than the first test with this same pellet, when they grouped 0.798-inches.
Eun Jins made a bad showing at 25 yards with the transfer port limiter installed. As long and heavy as they are, I guess they need all the velocity they can get, to obtain the rotational speed required for stabilization.
What have we learned?
The first thing we learned is this probably was not enough of a velocity drop to matter, except for the slowest pellet. The next thing we learned is that the changes are not always linear. Although three of the pellets exhibit what I would call a linear relationship of accuracy to velocity, only one of them — the Beeman Devastator — shows any real improvement. And even that is just a very small improvement that could just be due to chance.
The next thing we learned is that some pellets need their speed to maintain accuracy. The big heavy Eun Jins do not like this lower velocity, and I will predict they are going to get even worse with the next velocity decrease.
The Crosman Premiers are still not performing well, and since they are still within the transonic region, there is good reason for that. I look for an improvement in the next test.
What all this tells us is that using very long heavy pellets in a lower-powered airgun is probably not a good idea. When the distance to the target increases beyond about 30 feet, you will start seeing these pellets spread out, where lighter pellets will probably continue to be accurate.