How does rifling twist rate affect velocity and/or accuracy? Part 4

by Tom Gaylord, a.k.a. B.B. Pelletier

Announcement: Bill Cardill is this week’s winner of Pyramyd Air’s Big Shot of the Week on their airgun facebook page. He’ll receive a $50 Pyramyd Air gift card. Congratulations!

Big Shot of the Week

Bill Cardill is the Big Shot of the Week on Pyramyd Air’s facebook page.

Part 1
Part 2
Part 3

This could also be called the Twist-Rate Test. It’s a look at how different rifling twist rates affect both velocity and accuracy. The standard smallbore airgun twist rate has been one turn in 16 inches for all 4 calibers since the beginning of modern rifled airguns in 1905, and there’s been no published test that looked at any other rate. So, this is a first look at how different twist rates can affect an airgun pellet in flight.

I’ve selected an AirForce Talon SS rifle in .22 caliber as a testbed because changing the barrels is a 5-minute operation. I’m able to shoot every pellet in each barrel using the same basic powerplant. Because the Talon SS has adjustable power, I can adjust the power to different levels for each barrel and pellet and keep the test conditions constant.

A quick look
Today’s report is a summary of what’s been learned so far. I’ve tested the factory barrel and two experimental barrels with different twist rates. The test has been at three different power levels with two different pellets. While that all sounds simple, it gets complex quite fast; and this report is needed to put things into perspective for everyone.

I will not talk about percentages, nor will I show graphs that overlay one barrel against the others because, frankly, I haven’t done enough testing to support such a presentation. In the world of testing, what I’ve done is called a quick look — which means I ran a small test just to see how the data would play out. Any gross trends should be visible, but a lot of the data will remain hidden until more tests are done.

Proof of concept
The easy way to think of this is to think like an experimenter who wants to find out how well something works. Let’s take Melvin Johnson, the inventor of the model 1941 Johnson Automatic Rifle. He had an idea that he wasn’t sure would work, so he spent $300 of his own (borrowed) money to have a machine shop build a testbed. It wasn’t a gun — it was just an action and barrel. He tied it down and fired it from several feet away with a lanyard. All it did was show him that the idea was sound and workable. Today, this is called a proof-of-concept model.

And that’s what our two test barrels are — proof-of-concept barrels. They’ll tell us generally what the two non-standard twist rates (1:12″ and 1:22″) do relative to the factory Lothar Walther barrel that has a 1:16″ twist rate. If the results are wildly different, then we’ll know what direction our next tests should take. But we didn’t get wildly different test results. Let’s see what happened and speculate on what it means.

Two pellets and three power settings
I shot each pellet at three different power settings in each barrel. Before I get into a discussion of how things went, I want to caution you that every time I run this test the numbers are going to be different. You might think if that’s the case then why test at all. Well, although the numbers are different, they are still very close to each other.

So, we’re NOT looking for absolutes in this test. We’re looking for gross TRENDS. And I think we found some!

Fact 1. At power setting zero, the slower twist rate (1:22″) gives faster velocity
This is true for both pellets. As the twist rate slowed down (going from a fast 1:12″ to a slow 1:22″ rate), the average velocity increased EVERY TIME. Premiers went from an average 452 f.p.s. to 534 f.p.s. as the twist rate slowed down. JSB Exact 15.9-grain domes went from an average 434 f.p.s. to an average 521 f.p.s. But the factory barrel generally had the better velocity spreads. Not in all cases, but in most of them. While the factory twist rate is not as fast as a 1:22″ twist on power setting zero, it’s more stable.

This tells us that the faster twist rate does cause the pellet to slow down, as many people predicted. They often call it frictional loss, and I suppose that’s as good an explanation as any.

The other thing I want to say is that the Talon SS isn’t as stable at zero power as it is at higher levels. It wasn’t designed to be run at zero power, even though it is possible. The thinking is that if shooters are running at zero power they are either plinking ot shooting at targets that are very close. Either way, velocity stability doesn’t matter as much as it does on the higher power levels.

Fact 2. The slow twist (1:22″) barrel got to its top velocity earlier than any other barrel
On power setting 6, the slow twist barrel was shooting Premiers at an average 840 f.p.s. The factory barrel was at 818 f.p.s., and the 1:12″ barrel averaged 777 f.p.s. at the same power setting. At their top velocities (only on this test, remember), both other barrels hit just 846 f.p.s. (1:12″) and 849 f.p.s. (factory). The 1:22″ barrel went up to 854 f.p.s.

The same thing happened with the JSB Exact 15.9-grain dome, only the velocities were slower than with the Premiers.

What this tells us is the same thing the first fact told us: As the twist rate slows down, the rifle becomes more efficient.

And that would suggest several things. First and most important, that a slower twist rate will conserve air when all other things remain the same. The fact that I can get nearly the top velocity on power setting 6 means I can get a few extra shots per fill when using the slow-twist barrel.

The second thing is less important, but a slower twist rate will make it possible to achieve higher velocities. The difference, however, is so slight as to be insignificant. Compare 854 f.p.s. — the highest average velocity obtained on power setting 10 (from the 1:22″ barrel) with 846 f.p.s. — with the lowest average velocity obtained on power setting 10 (from the 1:10″ barrel). The difference isn’t worth the effort of getting a special barrel made since the factory barrel gives an average of 849 f.p.s. on setting 10.

Fact 3. The rifle gets the tightest velocity spreads at the highest power setting
This is generally true with all three barrels tested, though there was one anomaly. The 1:22″ barrel did have a tighter velocity spread on setting 6 than on setting 10 when the Premier pellet was tested. But the difference is only 3 f.p.s., and might just as easily have been reversed in a second test.

But the general trend for the velocity spread to tighten as the power is increased held for all three barrels and is probably a trend that will repeat with other pellets and at other power settings.

This trend doesn’t tell us as much about the barrels as it does about the rifle. It indicates that the Talon SS becomes more stable at the higher power settings — regardless of the twist rate. It does, however, make the next fact stand out.

Fact 4. The 1:22″ barrel produced similar power on setting 6 as on setting 10 with JSB pellets
This is the biggest discovery these tests have revealed. On power setting 6, the 15.9-grain JSB Exact domes averaged 817 f.p.s., while on power setting 10 they averaged 815 f.p.s. The velocity spreads for this pellet were 14 f.p.s. on setting 6 and 10 f.p.s. on setting 10. In essence, the power was at its maximum on power setting 6 with this pellet.

With the Premier pellet, the velocity was 840 on setting 6 and 854 on setting 10. And the spreads were 16 f.p.s. and 19 f.p.s., respectively.

So, the Talon SS develops its maximum power with these two pellets around power setting 6 when the 1:22″ barrel is used.

What does it all mean?
Given these gross trends, what can we take away from the testing that has been done to this point — if anything? I think it’s obvious that the gun is more efficient when the 1:22″ barrel is installed. However, I also want to note that all three barrels converged at power setting 10. None of the barrels were superior, as long as that power setting was used. But on power setting 6, the 1:22″ barrel is superior from the standpoint of velocity, alone.

If I can operate the Talon SS on power setting 6 and get max power, then I can probably get a couple more shots per fill of air before the gun falls off the pressure curve. Of course, that’s only speculation until I test it.

But what interests me now is how the rifle will perform on targets with the three barrels. In other words, is there a noticeable accuracy difference with one of the barrels over the other two? Or, conversely, is one of the barrels noticeably less accurate than the other two?

If the 1:22″ barrel were also more accurate than the factory barrel and the 1:12″ barrel, then we would have a great finding. I would also need to test the rifle with heavier and lighter pellets, to see if the trend continued. Or, is the factory barrel with its 1:16″ twist rate the best all-around compromise?

As I said in the beginning of this report, this is a huge test, and one that has never been published before. The goal is to learn more about how the rifling twist rate affects the performance of the pellet. I’m hoping that these trends we see today will continue as the testing continues, and we will at some point be able to make some educated assumptions about airgun barrel twist rates and their association with performance.

94 thoughts on “How does rifling twist rate affect velocity and/or accuracy? Part 4

  1. This trial shows i would assume that this would be of better use in the UK as we have to use the lower power settings by law, but only if the greater if only slightly velocity does not increase ft/lbs (it would be interesting too see what trends are set there).
    Change of subject here but it was some thing i read in the last report on the Falke that made want to ask. That is can any one suggest of any heavy pellets with thin skirts in .177 for hunting with my Airarms Shamal, sorry for air rifle name dropping but this rifle is awesome and i only recently received it as a present from the wifey. Anyway my reasoning is with a heavier pellet there will be more stopping power closer to your average weighted .22.
    I like to hunt with both calibers as both have their advantages at different ranges, quarry, etc and since my collection is growing thanks to an understanding wife (she likes plinking with a Crosman 2044 and 1077 and has just got a lurcher for coursing, so she’s happy for me to bring home dinner with my rifles) i have rifles for every occasion, i have to thank Edith for her excellent advice for my wife’s more understanding ways of my air rifle love. So if anyone can advise me on the pellet front it would be greatly endeared to them.
    best regards Wing Commander Sir Nigel Tetlington-Smythe.


    • GB,

      first off, my hat is off to you, sir, for actually eating what you kill. You are in a very rare community and I am not in that community. As for pellets, you will have to experiment with your Shamal to see what it likes but I have found JSB’s, H&N’s, RWS Super H’s and Crosman Premier pellets to be the most accurate in any of my rifles (no English ones, sorry). The most accurate pellet depends on the rifle and even among the same brand of rifles (Diana for instance,) a JSB will produce better results than an H & N in one rifle while the RWS might be better in another Diana. I would purchase a tin of each in the heaviest weights (if that’s what you are after) and run your own tests. BB does his testing from a bench rest and as you’ve discovered, shoots ten pellets per grouping at 25 yards.

      Take notes and label the targets – don’t ask why I advise that……

      Fred DPRoNJ



      • Fred,
        Speaking of eating what you kill: today’s paper has an article about a guy researching how to help some endangered turtles cross a road in Florida in order to breed and lay eggs. They have to cross a few times a year. He put a rubber replica of a turtle in the center of one of the lanes and observed the reaction of traffic since the larger percentage of turtle death was caused by traffic. The researcher was astounded at the number of times people would intentionally swerve to run over the turtle.
        -Chuckj



          • Oh, Good Lord. I don’t know how many times I have stopped on a country lane on my motorcycle to run back and grab a turtle and carry it to the other side of the road. I even did so once when in my car (cage to the Beazer). I don’t care if they were box turtles, snapping turtles or tortoises. I have a soft spot for those critters. No, I’ve never had turtle soup and would never shoot a pellet rifle at them.

            Fred DPRoNJ


            • Fred,

              I wasn’t saying that it was right to run over them. I was just pointing out that this is a possiblity.

              When we lived in Maryland, a baby starling fell out of the nest into the road in front of my car in a busy residential section of town. Starlings are pest birds, yet I stopped 2 lanes of traffic to retrieve the bird & take him to my vet. When another car saw it was just a bird that caused the traffic jam (but it was only for about 10 seconds), he stepped on the gas and nearly hit me. I don’t know if he’s got terrible aim and meant to run me over or if it was just a message that he didn’t care for saving birds.

              I think most people who don’t shoot (or who hate guns) would be surprised that people who have guns and have dispatched pests or hunted often times have a very big heart when it comes to animals and are quite merciful in the treatment of them.

              Edith


            • I have never killed or eaten Snapping Turtle. However, I have been present when some less citified folks have “rescued” one from the road to have it over for dinner. ~Ken


          • Edith, regarding the Snapping Turtle, you may be right. However, in this neck of the woods (S.E. Texas) Snapping Turtles are meat for the pot.
            Regarding saving the baby Starling, for me, it is all about “context” and you have offered a good example of that, something the impatient driver may never understand. ~Ken


        • Chuck, I have read of a similar experiment being done years ago by college students, who had the same finding, including some who backed up to run over the “turtle” again and one who tried to “peel out” while the “turtle” was under the rear wheel. I have no respect for anyone who deliberately runs over an animal. ~Ken


    • GB,

      My Shamal was a .22 caliber and liked Crosman Premiers. I think you call them Accupells. If I had a .22 Shamal, I would definitely give the 15.9-grain JSB Exact dome a try, as it usually beats the Premier in PCPs. My Shamal was FAC at about 20 foot-pounds, so that might make a difference, but I don’t think it will. I over-pressurized it at first, before discovering the starting air pressure was 2,600 psi, and my first shots were coming out at less than 12 foot-pounds. The rifle was still accurate at that power level, so I think if it likes a certain pellet, it won’t make any difference.

      Try the JSB Exact 10.3-grain dome in your rifle. I bet it likes it!

      My Shamal was very quiet, but had a disturbing spring buzz in the action. I fixed it by threading a rubber band through the striker spring coils, which was a 1980s trick to quiet the actions.

      Enjoy your rifle.

      B.B.



    • This trial shows i would assume that this would be of better use in the UK as we have to use the lower power settings by law, but only if the greater if only slightly velocity does not increase ft/lbs (it would be interesting too see what trends are set there).

      Uhm… by definition, an increase in velocity with no decrease in mass WILL increase the kinetic energy (and since the equation uses a square of the velocity, a small velocity change can have a much larger energy change than one might think).

      You have a 12ft-lb limit, don’t you?

      Let’s see if I can manipulate the calculator program properly…

      E = 12 ft-lbs
      M = 21 gr (.22 Baracuda class pellet)
      V => 507 ft/s

      Now, lets up the velocity to, say, 525, and solve back for energy…
      E => 12.85 ft-lbs

      At 550 ft/s…
      E => 14.10 ft-lbs

      As for the rest: Define “stopping power”? The phrase comes up in gun magazines and tends to always lead to two viewpoints:

      Light weight/small caliber projectile at very high speed (9mm pistol); possibly better ballistic coefficient?
      Heavy weight/large caliber at low speed (.45ACP), better sectional density?

      (The .40S&W attempts to split the two — halfway between 9mm and .45 in caliber, and velocity also between the two)

      Cons for LW/HS — bullet may either disintegrate on impact doing little actual damage, or pass right through the target (classic problem with 9mm ball) endangering those in the background.
      Cons for HW/LS — fewer rounds in a magazine, potentially more recoil, and a parabolic trajectory.

      For airguns, however, the point may be moot. Spring-pistons are most efficient within a range of pellet weights — go too heavy and the velocity takes a major crash, pulling the muzzle energy down with it; too light and the pellet may leave the muzzle before using all the potential energy in the air. Within the efficiency range, the velocity and pellet weight trade-off such that the muzzle energy is pretty much constant.

      Pre-charged tend to be more efficient with heavier pellets — since the back-pressure may help hold the valve open a bit longer [my theory, at least] leading to less drop in velocity than would be seen in a spring gun.

      But, in all cases, (ignoring the square and any constant terms)
      Energy = mass * velocity
      So if you are in a restricted energy environment, increasing mass will require reducing velocity to stay within the restriction.


    • I suspect it means a horse for chasing game animals…

      Might mean a dog though — but I’d bet on the horse (maybe simulated game animal)


    • Sir Nigel, taking a closer look at the South Yorkshire site shows they only offer the Rebel in .22 and I can’t help wondering if someone made a mistake (since no .177 is offered on the site). ~Ken


  2. Would it not be wild if the airgun manufacturers paid attention, most especially if your testing reveals a more accurate twist rate for airguns? Not that this is likely going to happen, since any change in production can be costly and besides, they know what we want even if we don’t.


  3. This is not suprising as .22 caliber rimfire rifles that are made for all calibers S , L and LR have a 1 in 16 twist rate . Before 22LR got popular any of the older rifles in 22 Short had a 1 in 24 twist rate which shot the lighter 29 grain bullet better ( 29 grain bullet at 750 fps). This is why in modern 22 rifles the 22LR shoots better (40 grains @ 1200 fps). BB You might find that the 1 in 16 is used due to more common availability of tooling,or economy of scale if purchased by the air rifle manufacturer. A very interesting read , very well done !!


    • Gene,

      You are right! I didn’t mention about the .22 short rifling twist rate, but it definitely is slower than the one for the long rifle. I’m pretty sure that the airgun twist rate is based on the long rifle rate and is now just being done because it works. And it may turn out to be the best rate of all, but that’s what this test is trying to establish.

      B.B.


  4. Please forgive me if you’ve already covered this in the comments for one of the previous parts of the testing. I was curious how much rotational energy the pellets have in the different barrels. For a given pellet and speed, the total energy is the usual linear energy (1/2*m*v^2) plus the rotational energy. In particular, I was wondering how much extra rotational energy the pellets had when using different twist rates. I was thinking that some of the lost pellet speed might be due to extra rotational energy. In case somebody else is wondering the same thing, I thought I’d post my work here.

    Rotational energy is 0.5 * I * w^2 (http://en.wikipedia.org/wiki/Rotational_energy). I approximated the moment of inertia as a hollow cylinder, so I = m*r^2 (http://en.wikipedia.org/wiki/List_of_moments_of_inertia). The moment of inertia for a real pellet is bound to be somewhere between the I for a hollow cylinder and a solid cylinder, so I picked the larger value. The rotational energy for a real pellet is bound to be somewhat less that I approximated here.

    I used the formulae from Wikipedia and Google’s calculation feature. Here’s the calculation for the 15.9 grain JSB in the 1:22 barrel:
    http://j.mp/VlQ6ah

    To compute the value for other conditions, replace the 22 with the twist rate, the 521 with the pellet speed, and the 15.9 with the pellet’s weight.

    I calculated for two conditions just to get an idea of how big an effect this is. For the 15.9 grain JSB in the 1:22 barrel, the rotating energy is only .0095 ft-lbs. The same pellet in the 1:12 barrel has .022 ft-lbs of energy. The bottom line is that the rotational energy is too small to explain the difference in pellet speeds.

    PS. Somebody check my calculation for errors!


    • Paul,

      ” The bottom line is that the rotational energy is too small to explain the difference in pellet speeds.”

      That says a lot. It is too small of a difference to cause that much effect by itself, but I think that when you add in the friction loss, and the air pressure drop curve, the difference in velocities will explain itself.

      Friction in a faster twist barrel should be more than a slower twist simply because the pellet contact area is in contact with the barrel for a longer total distance before exiting than in the slower twist, as compared in identical length barrels.

      Pressure drop over time in the barrel with the friction factor (whatever that may be, I’m not an engineer added in should take care of the difference. When you compare the remaining pressure at let’s say, the point where the pellet has traveled 2″down the barrel, versus the friction left to overcome before exit, then that result should be higher in a faster twist barrel than in a slow twist barrel and proportional anywhere in between. That number should be closer to the velocity ratios between the barrels on the same power setting than using the rotational energy loss number alone.

      Which is a long winded way of sayng that there are other factors that must be included if we’re looking to explain this phenomenon. And, there are even more contributing variables that I’ve probably forgotten to take into account here too…

      /Dave



        • And further cleanup… “identical length” should be “equal length”

          More factors/variables to consider. Hammer forged vs button rifle vs cut rifling will all give different results when all else is equal because they all have different degrees of bore finish (BB already hinted at this in a previous part). Rotational acceleration loss. Barometric pressure and relative humidity differences on coherent testing days, etc. Pellet batch (contact area) differences. Rifling land size in respect to how much less it has to deform at the start and how this will affect aerodynamics after exiting the barrel. Lots af things BB has done to mitigate these variables so we can find out the answer to the original twist vs accuracy question. A huge experiment! I like experiments! :-)

          /Dave


          • I think a lot of those factors could get lumped into a single measurement of the friction force for each pellet and barrel combination. I don’t see a way to compute the pressure drop off without knowing how long the valve is open.


            • Exactly! If we could find the formula to include at least the major ones, like friction, pressure, valve time, mass, and so on, we could end up with a number that would more closely follow the ratios of the barrels’ twist rate. The problem then being that every time we change barrels, our number would change due to differences in mfg tolerances which would affect the fit and finish of the bore and therefore how the pellet fits in it. So our number would be “good” only in the most general terms as to what’s happening inside the barrel. Once the pellet leaves the muzzle, it’s a whole ‘nother story…

              So, I’d guess that no matter how completely we can mathematically explain what is happening inside the barrel and how completely we can explain what happens outside after exit, the best we can hope for is “close”, and then after getting close, we have to test each individual gun for its pellet preferences anyway due to the tolerances…

              /Dave


    • I will be checking it. How did you convert grains to a mass unit? Why did you keep everything in English units where the definitions of mass and weight are not so easy to follow?

      –pz



        • It was not intended to be humorous. The English unit of mass is the slug; the unit of force is the pound. Going from “grains” to ounces to pounds and thence to slugs is a round-about route, and doing it that way is fairly likely to result in errors, either clerical or in units conversion. But all pellets are also rated in grams (mass in the CGS system) and in centimeters (length, also in CGS). So the only conversion you need to make is from BB’s velocity measurements in ft/sec to cm/sec.

          Frankly, I think the changes in linear velocity are due to additional drag induced if a pellet is rotating too fast and starts nutating when it gets near a critical rotational speed. It’s a fairly weak effect, but it does transfer energy from linear motion to rotational motion, and has the simplified effect of lowering the drag coefficient by increasing the effective diameter of the pellet.

          pz


          • Pete, forgive me but between you and Chuckj, I can see this as a dialogue between the characters Penny (Kaley Cuoco) and Dr.Sheldon Cooper (the very talented actor Jim Parsons) on the comedy series “The Big Bang Theory” – the non-technical person (Penny) versus the theoretical quantum mechanics physicist. It is funny and my apologies if I have offended either of you. You should watch an episode of the series.

            Fred DPRoNJ


          • Pete,
            Please don’t think I was being disrespectful. I thought it was funny because I am guessing that Paul is in the U.S. (inches and pounds) and you’re in Canada(?) UK(?) (centimeters and kilograms). Correct me if I’m wrong.
            -Chuckj


          • Pete,
            Just for the sake of argument, I think nutation might have more to do with the accuracy test — I expect to see the faster twist barrel either scatter or keyhole more at 50 yards. BB’s velocity readings are taken pretty close to the muzzle, though — I assume within a few feet, so it would be surprising to me if the nutation/precession effects were seen that quickly. Instead, I think internal ballistics is the place to look, and I think /Dave’s theory about friction and pressure drop are pretty reasonable places to look. The energy required to spin the pellet due to mass alone is almost neglible (per Paul’s calc.), but the difference in patch size (i.e. rifling in contact with pellet) could make the friction almost 2x on the 1:12 barrel versus the 1:22, couldn’t it?

            Right on about the conversions complicating calculation, although it is nice to have a front end that accepts common units (e.g. grains and f/s). The “slug” is something one rarely sees used!


            • I picked the units to be the same as the article. Google is very smart and manually converting units from the data in the article is a sure way to introduce mistakes. One of my favorite features is that you can get the answer in whatever units you like. Just change the “foot pounds” at the end to “joules” or “btu” or “electron volts” or even “horsepower seconds”. If you ask for units that doesn’t make sense, it just doesn’t return an answer. I have no idea how they distinguish pounds mass vs force or foot pounds energy vs torque. It’s magic.

              I kind of got the results I expected, but mainly I did the calculation that was possible. I’d like to do a similar calculation with friction,but I don’t think I have enough data. I don’t see a way to compute the pressure as the pellet moves down the barrel (it would be pretty easy with a spring piston gun) and we don’t know what the friction force is (but it would be pretty easy to measure with a bathroom scale and a cleaning rod).

              I’m usually fine with guessing, but this time it seems like a little more data would enable some computation to check the theories.


              • I wish I could edit that to say “horsepower fortnights”. It works. Try it.
                You can also say “cm^3 g / s^2″ if you’re dead set on sticking with the cgs thing, but where’s the fun in that?


          • Well Pete, I’d agree that there are so many different variables in the internal and external ballistics that is impossible to assign a cause with the data on hand.

            I would have said that the pellet precesses out of the barrel and that the yaw angle changes with time.

            Also having a yaw angle will increases the drag which lowers the BC. (I’m sure this was just a slip…)

            I”m at a loss to understand what kinds of measurements we amateurs could make that would define the ballistics problem better. The camera videos do provide intriguing qualitative evidence.

            Regards,
            Herb


      • PeteZ, good to see you in writing. I hope you are doing well. It is now 10 months since my cervical spine surgery. I have had some ups and downs. At the moment I think things are looking up. I have been able to get by on one 100mg Lyrica capsule many days while I required 2 per day for a few months since the surgery. I’ll see the neurosurgeon in mid January and get a 64 slice CT Scan done for him to look at.

        I have been able to shoot some. I have two decent CO2 pistols to shoot when I have the house to myself for a bit (or when the outside temperature warms up enough, which can happen here in S.E. Texas even in the winter during the day sometimes).
        ~Ken


      • Pete,
        I did not convert from grains – I let google do that for me. If you’d like to know how google did it, you can search for a simple conversion like “15.9 grains in grams”. It will return “15.9 grains = 1.03030267 grams”. Instead of converting every input myself, I find it simpler to just plug in the original units into the formula and then ask google for the results in whatever units I want. Often, if I have a mistake in the formula, google will refuse to return the answer in the units I expect, which is a sign for me to review and edit the formula.


  5. BB,
    I haven’t commented much on the data, because there is still a lot to do, but I think it is important and a little exciting for a geek like I can be. I can’t wait to see the accuracy results.

    One thing that is already exciting to me from the velocity vs. power data, however, is that springers might benefit even more from a slower twist rate than the PCP you are testing. If it gave the manufacturers a way to increase VELOCITY, they might jump on it :)! I think the PCP is the right vehicle for initial testing, so this is just an observation, not a work request :)!

    I remember asking you years ago about how they determined the proper twist rate, and you said that the first rifled airgun barrel (BSA?) was likely just the same as their .22 (RF)! Probably you are the first to actually test different twist rates on purpose. Modern rifling machinery is pretty easy to change twist rate, I think, so keep digging!


  6. Funny thing: I got the H&N Sport Match-Box, the one that holds 100 pellets for competition shooting, for Christmas. I opened up the box and inside were the instructions for opening up the box. Now, it wasn’t that hard to figure out how to open the box but don’t you think that if you were going to write instruction for opening a box you’d put them on the outside of the box?
    -Chuckj


    • They were placed in the box because if you are someone who actually needs directions……..you might be prone to misplace them! Some companies are VERY thoughtful.LOL



    • I just found out, there’s a special Gub’ment agency (yup, our tax dollars at work) that deals specifically with these kinds of “Doh” challenges. It’s the Department of Redundancy Department. Happy New Year ya’ll. Shoot/Ride safe, Beaz




      • Looks like Wulfraed’s comment about his gun list has some sort of code that has messed things up. I’m going to delete his message & see if it returns the RSS feed. I downloaded the feed and it ended at the at the start of Wulfraed’s comment. I don’t understand these things, but I’m guessing it has something to do with the combination of symbols & letters.

        Edith


        • Strange…

          I think the ampersand was the only sensitive character in the mess, and I’m sure I’ve used it before.

          And we’ve seen the results of a mistyped blockquote before — typically either nothing is quoted, or my reply becomes part of the quoted text.

          {Whereas Earthlink email was down from ~330PM EST to 930PM — both mail arriving in at Earthlink and the POP3 connection checking for new mail to download; hopefully the various sending servers will retry the blocked messages over the next few ours}



  7. BB,Backing up,I understand that men rifled barrels to stop projectiles that were longer than wide from wobbling and even flying end over end.This was bad because it ruined accuracy and robbed downrange velocity.From the first mention of this exciting testing I suspected that the 1:16 twist was generally right for the diabolo pellet shape.What I envision is a tipping point of shape and weight distribution in a pellet design.If this tipping point is passed ,then the general twist rate would not be able to overcome the pellet’s tendency to wobble or end over end when added to the gun’s own vibration effects and the shooter’s influences.If this is correct then accuracy for the larger number of pellets we use today won’t be improved by the different twist rate.However these other rates may help improve accuracy for those pellets we have that fall past the tipping point(my idea)in their design.This would allow us to use some of those pellets we previously called junk(unless they are damaged or of lousy manufacture anyway).–As for the gain in velocity with the slower twist rate;my vote is a loss in stability for most pellets and especially past 10 meters.They will likely lose that velocity ,and maybe more, and arrive at their target with less than they would have with the standard barrel.They may even totally miss the target and hit the broad side of the barn.–Tin Can Man-


    • RE: “What I envision is a tipping point of shape and weight distribution in a pellet design…”

      Harry (Yrrah) on the yellow put forth a notion to which I agree. EVERY pellet reaches a point where the pellet stops precessing and starts spiraling. It is really just a case of how “far” downrange. Harry has also suspected that pellets with a slower spin rate would be more stable at long ranges (shooting say at 100-200 yards).

      “Far” defining the critical point where the interaction between aerodynamic drag (as function of velocity and yaw angle), the two moments of inertia, and the spin rate causes the change between precession and spiraling.

      The “problem” here is that no one has proposed a “useful” equation which relates the above factors in a “simple” equation. For a given pellet design the two moments of inertia are fixed. For a muzzle velocity with a fairly low spread, then the initial spin rate is fixed too. We could measure velocity and spin rates at various distances. (Unfortunately precision is poor…)

      “Simple” equation meaning one that is good enough for us amateurs to use. The military has microwave radar and computer models which are beyond the reach of amateur pocketbooks.

      Regards,
      Herb


    • I believe rifling appeared even in the days of round-ball (which was probably loaded with bumps and air-pockets). Isn’t that one of the defining differences between a rifle and a musket? Muskets having about the accuracy (and range) of a shotgun with a slug load… (Without the benefits of a badminton birdie stabilization that hollow base slugs have)

      Non-round projectiles were much later — the “Minie ball” period…


      • You are right in general. Round ball rifles were rifled, generally with a pretty slow twist (e.g. 1:48 was the norm, about one turn in the length of the barrel); modern round ball rifles are even slower in calibers over .40, e.g. 1:66 or 1:70 for a .50 caliber. Pistol barrels were rifled faster (e.g. 1:20) when they were rifled, due to the generally lower velocities. My take is that the intent was simply to induce enough spin to even out any flaws in the ball. They are definitely more accurate than smoothbores, even when the smoothbore is loaded tightly. Many military muskets were loaded somewhat loosely to facilitate quick reloading, and their accuracy was pretty abysmal. The American longrifle could hit a man at 200 yards fairly regularly, and longer shots were recorded. Many reports of smoothbored muskets make it clear that hitting a man at even 50 yards was a matter of luck. The musket was intended for conventional warfare, i.e., lines of soldiers firing volleys. The American riflemen (and they were relatively small in number) changed the game by being able to aim accurately beyond the effective range of musket fire, and they harassed and horrified the British by shooting officers by preference :).

        Alternately, there were “bullets” used much earlier (on some German Jaegers for example) and they seem to have been rifled fairly fast. Those barrels were short (e.g. 30″ might have been average) and one turn for the whole barrel length seems to have been common. They weren’t terribly accurate at long ranges, I don’t think, but better than smooth bores and the bullet allowed a heavier projectile without increasing the bore to outrageous proportions. Hunting in Europe appears to have been a privilege limited to the upper classes, and they normally took quite easy short-range shots. I think the problem with “bullets” in fast twist barrels is that they required a lot of effort to load, especially on a fouled bore. The Minie ball worked around that problem somewhat by loading loosely but having a thin skirt that bumped up and engaged the rifling when fired. The rest is history, I suppose…


      • This has got me thinking about shotgun slugs. As we know, shotguns are smooth-bores, so spin stabilization in the slug is induced by molding angled projections (like driving bands) into the side of the slug.

        Since we are dealing with a heavy, low-velocity projectile, wouldn’t there be a ballistic advantage in shaping a shotgun slug like a diablo pellet? It could then be drag-stabilized. The weight bias to the front of the slug would further stabilize it.

        Les


        • Shotgun slugs (the ‘rifled’ ones) ARE drag stabilized. The “rifling” on them serves two primary purposes. It makes it easier to shoot them through a choke (not as much lead to squeeze down), and it sells the slugs. It may also add to turbulence and drag.

          Unless you have one of the rifled slug barrels , the slugs will not spin. There is no structure in the bore to grip the sides of a slug and spin it in a smoothbore.

          twotalon


        • Les,

          There ARE shotgun slugs shaped like diabolos. The Balle Blondeau was a very successful one from France. There are even molds that cast shotgun slugs in the shape of diabolos.

          B.B.


  8. B.B.

    “I had a dream” – an air rifle rifle with twistable barrel, adjustable in the same manner as speed, by a turn of the wheel. Controlled carbon nanotubes or nanite super euctatics anyone? :)

    Anyway, B.B. you do a tremendous job, Cardew-sized I’d say. From what I’ve read from your post – it’s all quite in line with my theoretical musings and I’m glad that I was on the right way. What I’m really waiting for jumping on my seat is accuracy tests with each barrel.

    Another thing – you may, or may not have noticed it – but there are such things that I call an inherent (barrel’s) and affected (barrel fouling) accuracy. I suspect that twist rates that slow the pellet down at high power settings will also be more prone to lead fouling thus losing accuracy much faster. So it may be like that – a barrel shoots laser-like, but also looses accuracy laser-fast in 150-200 pellets. Is there any tip on a dependency like that?

    duskwight


    • More friction (assuming that is the culprit) should equal more fouling, so you might be on to something! I think the 1:22 barrel is going to be the most accurate and that the 1:12 will corkscrew noticeably by 50 yards, but theories and facts are two different things, so we’ll have to wait and see :)… The velocity data is already proving interesting, although I didn’t really care that much about it at the beginning. I would somewhat prefer to see the velocities equalized for the accuracy test, but BB is already overworking himself!


    • duskwight,

      Three things come to mind to keep the leading down as the twist rate increases. First is to keep the top velocity low. Of course that flies in the face of what most shooters want, but there you are.

      Second is to use a pure lead pellet. Whenever a projectile has any antimony in it, it tends to lead very fast. I see this with rifle and pistol bullets in firearms all the time. We call them hard lead bullets and they are horrible leaders — especially in handguns.

      Third would be some sort of protective coating on the barrel metal. I use a product called Sweet Shooters that seems to eliminate or reduce leading in firearms quite well. It is applied to a clean barrel and the liquid seems to bond with the metal in the barrel. After an applications the barrel seems easier to clean the next time.

      B.B.


      • BB,

        Less fouling also seems to be true using dry moly. But that stuff is so messy that I don’t use it for much anymore… I’ll try the Sweet Shooters product you mentioned.

        /Dave


      • B.B.

        I was quite surprised that harder bullets/pellets leave more lead. I always thought it’s like pencils – the softer the thicker line it draws… Well, live and learn.
        Can you drop me a link on that product? I couldn’t google it by its name, all it gives me is alcohol cocktail recipes – maybe it’s due to closeness of the New Year :)

        duskwight



        • This would seem to be counter-intuitive, but it is true. I shoot a variety of different pellets from different manufacturers. It is the hard pellets from Crosman that will leave a deposit in the barrel (and on your fingers). I never would have thought that was from an alloy in the pellets themselves. I thought it was from a graphite coating on the pellets that acted as a lubricant.

          It takes a great amount of these pellets to leave enough deposit to affect accuracy. I generally clean the barrels on my air guns when they are new (to clean out any crud from manufacturing, sometimes I find odd stuff in there), and do not clean them again unless I notice a drop in accuracy. The JB non-embedding bore paste I found described in this blog does a wonderful job.

          I don’t mean this to be a criticism of Crosman pellets. They are some of my favorites, and, in my opinion, are a fine balance of quality and price. We should all wash our hands after handling lead anyway.

          Les


          • Les,

            The stuff on your fingers IS graphite. That’s not what the pellets smear against the walls of the bore. That is lead.

            Bullets that are hardened with antimony are notorious for smearing lead on rifle barrels. Pure lead bullets don’t do it nearly as much, but they also cannot be accelerated to velocities as high as hardened bullets, so we are stymied.

            Antimony creates a higher coefficient of friction that melts off lead as it passes through the bore. So it is best to either stick with pure lead, or keep the velocity low enough that the pellets don’t smear or use a lubricant that protects the bore when you shoot.

            B.B.


  9. Thanks everyone, and B.B, it was your artical and then seeing a Shamal for sale that got me tempted, when i went to look and held it i instantly fell in love with it, this was from a very good gunshop in gloucester who let me pay for it in installments, and i would imagine would have the pellet you suggested as they have a rather large range of all things gun related. yours was the only information i have found on the net about Shamals apart from a few bits when someone is selling one on a forum, though i did find a maual for the 100 series which is basically the Shamal with S200 stock and a seperated muzzel suppresor and filler cap http://guns-nn.ru/manuals/manual_airarms_njr100_en.pdf.
    well i hope you all had a slendid christmas, soltice, etc, and a happy new year.

    best regards wing commander Sir Nigel Tetlington-Smythe


  10. P.S. A lurcher is a cross breed of usually a working dog (border collie or bedlington terrier in our case) and a long dog (greyhound or whippet in our case), you would train one to whilst walking through a field to on command chase and bring down a rabbit or hare, and that is called coursing, very popular amonst the travelling folk, working class and gentry of this part of the world.
    I’m sure i’ve missed out some minor facts but that is roughly translated ‘coursing a lurcher’.


    • Sir Nigel,

      Thanks for translating that for me. We are certainly” two peoples separated by a common language.”

      Maybe you could translate something else for me. My wife gave me a book for Christmas titled “Gun. A Visual History”. Sort of a coffee table reference book illustrated with beautiful color photos and illustrations of all sorts of light firearms.

      There was an illustration of a firearm used for hunting rooks and rabbits for making a traditional dish called a “rook and rabbit pie”. I’ve eaten my share of both rabbits and pies, but what is a rook?

      Happy New Year.

      Flotilla Commander (Lt.) Les Foran, USCGA



      • Yes, Mike is correct a Rook is a Black Bird. There is even a card game called Rook that I played back in the 50′s. I wonder if it still exists? Thanks for the memories. I’ll have to look that up. Also I think Heckle and Jeckle were Rooks. Hah! how many remember them?
        -Chuckj


        • Gee, I thought they were crows.

          In New Mexico, we have ravens. Sort of like big crows on steroids.

          In Colorado, we have magpies. Big, ornery black and white crows.

          Les


          • Desertdweller,
            It turns out YOU and MIKE are correct and I must bow to a Midwest semantics misunderstanding. Here’s what I found on Wikipedia:

            The Rook (Corvus frugilegus): is a member of the Corvidae family in the passerine order of birds. Named by Carl Linnaeus in 1758,[2] the species name frugilegus is Latin for “food-gathering”.

            Rooks are distinguished from similar members of the crow family by the bare grey-white skin around the base of the adult’s bill in front of the eyes. The feathering around the legs also looks shaggier and laxer than the congeneric Carrion Crow. Collective nouns for rooks include building, parliament, clamour and storytelling.[3][4] Their nesting patterns gave rise to the term rookery.

            The Common Blackbird (Turdus merula):
            is a species of true thrush. It is also called Eurasian Blackbird (especially in North America, to distinguish it from the unrelated New World blackbirds),[2] or simply Blackbird, where this does not lead to confusion with a similar-looking local species. It breeds in Europe, Asia, and North Africa, and has been introduced to Australia and New Zealand.

            [BTW, Turdus merula opens the door for many more questions and describes some of the wine I've experienced this Christmas.]

            It may not immediately be clear why the name “Blackbird”, first recorded in 1486, was applied to this species, but not to one of the various other common black English birds, such as the Carrion Crow, Raven, Rook or Jackdaw. However, in Old English, and in modern English up to about the 18th century, “bird” was used only for smaller or young birds, and larger ones such as crows were called “fowl”. At that time, the Blackbird was therefore the only widespread and conspicuous “black bird” in the British Isles.

            I hope this resolves any confusion I may have introduced.

            This may seem way off topic but I feel this is airgun related since I believe these are the critters most impacted by airgun enthusiasts
            -Chuckj


            • Yes, I have had bottles of wine that fit that Turdus Merula definition. The last being a “allegedly” very expensive bottle my brother-in-law brought over. I thought drain cleaner would have been better than that bottle and the thought passed through my mind he was trying to kill me.

              Fred DPRoNJ


            • That’s odd this comment finally showed up, and in the right place, too. The sheer volume of words must have slowed it down. At any rate I do hope this benefits mankind or at least the kind men and women on this blog.
              -Chuckj


  11. B.B., as I fell asleep last night I have an interesting hypnogogic experience. It was a kind of Rube Goldberg mechanism that rotated the pellet to high RPMs during the first stage of trigger pull so that the pellet was already rotating before it even started its forward motion. Of course this would necessitate a kind of cylinder for the pellet and extra mechanics (probably battery powered) and would work in a smooth bore barrel.
    There is such a wide gulf between imagination and reality.
    ~Ken


    • Ken,
      I think electric would add heavy motors and batteries however, if the cocking lever wound up a spring that was released prior to taking the shot (might be a good reason for a three stage trigger) your dream might be reality. adding a coiled spring wouldn’t add much weight I wouldn’t think.
      -Chuckj


      • Chuck, you remind me of the toy cars we used to play with; the ones that used a little flywheel. Once it was spinning sufficiently it kept the momentum up for a while. One problem I see is that the pellet would have to be at the hub of the wheel, making the operation more complicated. Still, I can see your idea of the spring being wound up when the gun is cocked, then setting the cylinder in motion as the appropriate stage of trigger stage is reached. Okay, we have the 10% inspiration; it’s the 90% perspiration that may be the bottleneck. ~Ken


  12. I’ll be interested to see a few holes in some targets to see if there is any difference in accuracy but I suspect there won’t be much of a change.


  13. I was just wondering if anyone has pushed a pellet through a bore with a cleaning rod by putting the end on a scale to measure the friction of different pellets, to see if it affects accuracy . It might also tell if twist rates have much effect on friction.


    • You will have some problems pulling that off….

      All you have to do is push a pellet though a bore and you will see why…. loose and tight spots, and smooth and rough spots. Any friction difference between different twists will be insignificant in comparison.
      There will also be no guarantee of how accurate the barrel will be based on this, even if you could measure a friction difference based on twist rate.

      twotalon



      • Exactly, some pellets are going to go through those places with less effort than others either due to size or hardness. I think it would be interesting to see which ones would group better .
        Not just twist rate is involved, there was a lot of math being used to figure that out . I thought measuring it would be easier, could very well be completely wrong. Would not be a first.


        • shaky…

          What we need to do is put the math aside. We are not dealing with only one kind of pellet or one velocity.
          We are not dealing with just the best quality pellets either.

          We will probably find that different twist rates and velocities are not going to work the same with an assortment of different pellet designs. The biggest differences may be with the pellet designs that are notorious shotgunners at distance. Some designs will be more forgiving than others about stabilization requirements.

          It will probably come down to the point that one size does not fit all. At that point, what will be the best compromise ??? But that is still with only one barrel of each kind.

          twotalon


  14. Comment test…. I just submitted a larger comment and it hasn’t shown up. This is a test to see if it’s me or the comment.
    -Chuckj


    • OK, this one showed up so I don’t know what happend to the previous one. It contained a definition of Rooks and crows and blackbirds. Bottom line: a Rook is indeed a Crow and not a black bird.
      I’m glad to have straightened that out before I ruined anyones lives.
      -Chuckj


  15. Hi Tom,

    I’ve seen rumors on several forums online regarding an impending change of Air Venturi’s handling of the higher end Beeman air guns–specifically Weihrauchs. Posts stating that soon Air Venturi will no longer be the importer and/or Weihrauchs will no longer brand any of their air guns as Beemans.

    Do you know anything about this that you would be allowed to share? I believe I know one possible source of the rumors but many of us Weihrauch (and Beeman) fans are curious.

    Thanks!

    Jerry



      • Thanks for the quick reply! I also got an email from Val Gamerman stating the same thing but you know how the Internet is. A few well-informed replies don’t stand a chance against a good conspiracy theory.

        The current thread is in GTA and the misinformation begins about here: http://www.gatewaytoairguns.org/GTA/index.php?topic=40416.msg377699#msg377699

        I posted your reply as well ad Val’s. I understand if you might need to remove the above link after looking into it.

        This comes up on the Yellow forum for time to time as well.

        Best regards,

        Jerry R (jdub on GTA)


        • Jerry R,

          I read the thread. Mark is strangely under the impression that Dr. Beeman is still somehow involved. He’s not. He sold company & the brand (20+ years ago) & allows the use of his name for the guns associated with company. So, I’m unsure why he thinks there may still be dealings between Dr. Beeman & HW. The dealings & contracts are between the supplier/exporter (Weihrauch) and the importer/distributor (Air Venturi). The info I provided to you is from my same source (president of Air Venturi). No one else has firsthand info.

          Edith


          • Thanks again. I think this is just the Internet doing what it does best. Giving people without factual information a place to present their rumors as if they were fact.

            I have been dealing with Pyramyd for years and received a phone call from Mr Gamerman a few months ago after I’d had a couple customer service problems. He was a true gentleman as we spoke. Accepting responsibility for the foul ups, never attempting justify why the issues happened, and he seemed very interested in ideas on how Pyramyd could improve customer service. I enjoyed talking to him and in the end he made sure that all issues were resolved in my favor–very generously in my favor. Because of that I have every reason to believe him when he answered my question about Beeman.

            BTW, I also really enjoy this blog. It’s a testament to both Tom and Pyramyd that he is able to write so honestly about products Pyramyd sells even though the reviews can sometimes be pretty harsh. :-). I know a lot of people appreciate that honesty on Tom’s part and Pyramyd for allowing Tom a free hand.

            Regards,

            Jerry R


        • I followed this link and found the following statement from “jdub”:

          “In any large group of people you have some who are uninformed, some who think they are informed, some who have accurate information, and some that create their own information based on their opinions and theories while having no actual insight into the internal workings of a product or company. You mix that all together and you have created an online forum.”

          I rather enjoyed that statement. Very profound. I find the category I fit in progresses over time spent in the forum.

          -Chuckj


  16. I apologize for posting old info in regards to this, I and some others were not up to date on the changes after the fact, I was merely replying to what another poster had said on the subject, so Thank you Edith for clearing this all up for us, Jerry R in new to the forms and just trying to make a name for himself!


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