How does rifling twist rate affect velocity and/or accuracy? Part 3

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

Part 1
Part 2

This is a test of the effects of rifling twist rates on both the accuracy and velocity of pellets. I’m using a standard AirForce Talon SS rifle in .22 caliber and there are three barrels — each with a different twist rate. The factory Lothar Walther barrel has a 1:16 rate, and there are two barrels made by Dennis Quackenbush. The one we already tested has a 1:22 twist, and today we’ll look at the velocity produced by the 1:12 twist barrel.

I used the velocities for the factory barrel from an earlier test in the last part, so today I’ll also test the factory barrel at the test settings and report those results, as well. Let’s get started.

Power setting 0

Factory barrel
The factory barrel delivered an average 480 f.p.s. on setting zero with Crosman Premier pellets, and the range went from 468 to 502 f.p.s. The spread was 34 f.p.s., and the average energy was 6.96 foot-pounds.

JSB Exacts, which weigh 15.9 grains, averaged 469 f.p.s. from the factory barrel. They ranged from 440 to 492, for a spread of 52 f.p.s. At the average velocity, they produced 7.77 foot-pounds of energy.

1:12 barrel
Premiers averaged 452 f.p.s. on setting zero with the 1:12 twist barrel. They ranged from 422 to 478 f.p.s., which is 56 f.p.s. At the average velocity, they produced 6.49 foot pounds of energy.

JSB Exacts averaged 434 f.p.s. on power setting zero with the 1:12 barrel. The spread went from 407 to 450, which is 43 f.p.s. in total. At the average velocity, they produced 6.65 foot-pounds of energy.

Power setting 6

Factory barrel
On setting 6, Premiers in the factory barrel averaged 818 f.p.s., with a range from 801 to 828. So, the spread was 27 f.p.s. At the average velocity, Premiers produced 21.25 foot-pounds of energy.

JSB pellets produced an average 794 f.p.s. in the factory barrel on power setting 6. They ranged from 780 to 807 f.p.s, so a spread of 27 f.p.s. At the average velocity they produced 22.26 foot-pounds of energy

1:12 barrel
On setting 6, Premiers in the 1:12 barrel averaged 777 f.p.s. with a range from 734 to 797. The spread was 63 f.p.s. At the average velocity, Premiers produced 19.17 foot-pounds of energy.

JSB pellets in the 1:12 barrel on setting 6 produced an average of 786 f.p.s. The range was from 763 to 804 f.p.s., for a total spread of 41 f.p.s. At the average speed, the energy was 21.82 foot-pounds.

Power setting 10

Factory barrel
On setting 10, Premiers in the factory barrel averaged 849 f.p.s., with a range from 846 to 851. The spread was 5 f.p.s. At the average velocity, Premiers produced 22.89 foot-pounds of energy.

JSB pellets produced an average 829 f.p.s. in the factory barrel on power setting 10. They ranged from 825 to 831 f.p.s, so a spread of 6 f.p.s. At the average velocity, they produced 24.27 foot-pounds of energy.

1:12 barrel
On setting 10, Premiers in the 1:12 barrel averaged 846 f.p.s. with a range from 838 to 854. The spread was 16 f.p.s. At the average velocity, Premiers produced 22.73 foot-pounds of energy.

JSB pellets produced an average 830 f.p.s. in the 1:12 on power setting 10. They ranged from 824 to 839 f.p.s, so a spread of 15 f.p.s. At the average velocity, they produced 24.33 foot-pounds of energy.

Observations
First, I’ll note that the velocity didn’t change much when I tested the factory barrel with Premiers on the test settings, but it did change significantly when tested with JSB Exacts. That poses no problem for this test because the next report will be one with all three barrels compared, and for that one I’ll use the test data collected from actual testing with the factory barrel. So, the estimated velocities of the first test will be replaced by today’s data.

The second observation is that on the lower power settings the factory barrel produced higher velocities than the 1:12 barrel. But on power setting 10, the difference was much closer. I’ll have to look at the results of the 1:22 barrel; but as I recall, it was superior in the middle power range.

What’s next?
Next, I will put all the data together so we can analyze them. I want you to remember that this is just the first cut at testing these barrels. This is just to point us toward the directions we should explore.

Of course, the accuracy test that comes next will tell us more about each barrel, and that may reflect back on this velocity test.

If you find today’s data confusing, don’t be discouraged. When I put it together, it should make more sense.

47 thoughts on “How does rifling twist rate affect velocity and/or accuracy? Part 3

  1. Well, don’t all of you comment at once. It’s hard to keep the comments straight! ;)

    I guess the raw data are just not that interesting. But the test will continue, nevertheless.

    B.B.


    • O.K. O.K. …..
      I will tear myself away from the SyFy channel and my pellet inventory long enough to say something….

      Since there is not much velocity difference between power setting 6 and 10, why bother with setting 6 ? You are still on the front of the curve at 6, and on top of the curve at 10. It probably got there by 8.

      twotalon


      • TT,

        While that is true of the 1:12 barrel, remember the 1:22 barrel actually was faster on setting 6? That’s the sort of stuff we are learning from this test.

        B.B.


        • B.B.

          Rather than the little power plant quirks caused by backpressure differences, I am most interested in one thing….

          The divergence difference between 25 and 50 yds. Which twist will show the least divergence when doubling the distance.
          Not that it really matters, because the airgun companies will not spend the money on different twist rates for different pellets.

          Might have been interesting to see what would happen with different twist rates when shooting pellets that are notoriously unstable.

          twotalon




              • TT,

                Which is the point of this test. The twist rate for air rifles was selected arbitrarily in 1905, and in all the intervening time nothing has changed. So this test is a look at what works and how well it works. And, yes, accuracy is going to be tested, but a lot of people had thoughts about the effects of twist rate on velocity, so that had to be tested, too.

                B.B.



    • BB, what length are the barrels Dennis made for you? From the picture, I am thinking they are 12″ long.

      Another question is did you polish the barrels Dennis made for you with the bore paste? I was thinking that that would make them match your stock barrel better.

      David Enoch


      • David,

        The barrels are all 12 inches long and no, I didn’t clean them with JB Paste. I will do that before the accuracy t6est.

        B.B.


    • Not sure, but I think there was an RSS feed issue within the last 24 hours, but it’s gone now…

      But as to the current test series… You are listing high/low and average (mean?) velocity… But for a cross barrel/cross power comparison, being provided the mean and standard deviation may be more useful to the budding statistician. One could then attempt statistical tests to determine if the difference in mean velocity is meaningful or can be explained away as just normal sampling difference.

      For example:

      mean 550fps sd 2fps
      and
      mean 560fps sd 2fps
      are distinctly separate results — 3sd would give 556 and 554, respectively; a very small propability

      mean 550fps sd 5fps
      and
      mean 560fps sd 5fps
      would give a 3sd overlap of 565 and 545 respectively — higher probability the two runs are from the same performance.


  2. Tom,

    Since I have very little experience with the talon/condor platform I have a newbie question.

    When a pellet is inserted into these guns does it engage in the rifling of the barrel(s)?

    Here’s my real question. Are all types of pellets that you’re experimenting with fit the same in each of the 3 barrels or are pellets tight in some and loose in others? In this same vein, did you use the jb bore paste treatment on these new barrels before starting this test?

    kevin


    • Kevin,

      AirForce has been putting a leade in the breach of their 24-inch barrels for quite some time to facilitate loading. These 12-inch barrels don’t seem to have the same leade, but since I don’t have a modern barrel in my gun, that isn’t the last word.

      Quackenbush barrels have no leade but they do have a shpry tapered breech entrance.

      The pellets loaded easily in both barrels in this test .

      B.B.


      • Tom,

        Thanks.

        “shpry tapered breech” ? Assume you meant to say short tapered breech?

        I know you’ve said all along that this is not an accuracy test. It’s not about pitting Dennis Quakenbushs’ barrels against LW but I’m still curious if you have or intend to clean his new barrels prior to the accuracy testing.

        kevin


        • Kevin,

          I hadn’t planned to clean either barrel, but since you are the second person to ask, yes I will clean them both. Both look like very nice barrels.

          B.B.


    • Kevin…
      Let me whizz in your corn flakes…..

      I have several LW barrels made for AF rifles. Does not matter if they are .22 or .177. Pellets fit differently by quite a bit from barrel to barrel. Optimum tune changes when changing barrels.

      twotalon


      • twotalon,

        It’s ok. I don’t eat cornflakes.

        Guess common sense should have answered my question since barrels can differ dramatically even from the same maker. As my grandmother used to say, “common sense isn’t common”.

        kevin


        • kevin…

          When I was in the AF, I often heard the expression “common sense will prevail”. It never did. Seems to be the same in Washington (DC).

          twotalon


  3. Hello BB and all:

    Help me, for I am new and ignorant. I have had a Crosman 1377 for the past few months, and have recently purchased my first rifle, a Air Venturi Bronco. I like it a lot, but have a few questions I have for you and the experienced ones.

    1) I have read here before that the oil port on this rifle has been closed up to prevent overzealous chamber oiling. What should I do to maintain the rifle?

    2) I can’t seem to seat pellets far enough into the breech by hand. The ends of the pellet skirts are getting sheared off and smeared onto the breech face when I close the action. I can pop the pellets farther into the breech with a screwdriver (obviously not an ideal long term solution), but that still often smashes the skirt or shaves some of it off. This happens with Hobby, Superdome, and Gamo pellets. I figure this isn’t doing anything great for accuracy, but my bigger concern is the sizable lead shavings on the breech flying off wherever when I open the action. I had hoped to use the rifle on my indoor range, and while I’m not super-paranoid and I try to keep everything clean, I’d still like to keep loose lead to a minimum. Is this normal, or is it something I should have the gun serviced for?

    Thanks,
    –Matt


    • Easy to fix…

      I had the same problem with one of my rifles. The skirt bottomed out on the chamfer before seating flush.

      I used a bullet shaped dremel stone to carefully deepen the chamfer until the skirts would seat flush. The work was done by hand, and not with a dremel tool. It did not take much twirling and rubbing to get the job done.

      twotalon


    • Matt,

      You do NOTHING to maintain your rifle except shoot it. After 10,000 shots, MAYBE you’ll need to oil it, but don’t worry about that now.

      As for the pellets not seating deep enough, use a ballpoint pen to seat them. A Bic works well for this. Puramyd Air even sells a pellet seating tool that can be adjusted for different depths of seating. It’s here:

      http://www.pyramydair.com/s/a/Pellet_Pen_and_Pellet_Seater_Loads_Seats_177_Pellets/4140

      Shoot, shoot, shoot that rifle! And tell us how it does. remember to use the artillery hold for best accuracy. You can learn about that here:

      http://www.pyramydair.com/article/The_artillery_hold_June_2009/63

      And welcome to the blog!

      B.B.


    • Matt,

      Welcome!

      Use an old, used up bic pen to seat your pellets. Just push the point into the center of the pellet inside the skirt and you’ll feel the pellet snap forward into the breech.

      Just keep the outside of the gun clean and oiled. Oil the moving joints occasionally with a drop of mineral oil. After a few thousand shots, it may start making a honking noise. You’ll know it when you hear it. It sounds about like a goose. Then just drip a few drops of silicone based oil down the muzzle and let it stand on its butt for a few hours/over night. Should be good to go!

      /Dave



    • Thanks all, the bic works nicely for pellet seating. If I decide the little shavings that are left bug me, I’ll try twotalon’s bullet bit solution. B.B., I’ll work on the artillery hold. Is there anything special about air pistol technique I should know?


  4. BB,

    I’m on some days off here so I get up late… But this test is fascinating and analyzing the raw data is half the fun!

    It is interesting that the 1:12 DQ barrel caught up in velocity on setting 10, as well as the slower 1:22 appearing to be more efficient on setting 6. I wonder if you can put all of these types of anomalies, or observations together in red font or in a different section at the end so we can look at all of the oddball stuff together? Since this will be a many part report, maybe keep the odd stuff on a running list at the end of each report? I’m assuming there will be more oddities to report…

    Or, maybe you’d rather have us discover and discuss them on our own, but you could add the discoveries to the top of the next report…

    /Dave


    • Dave,

      That is what the analysis section is all about — making sense of all that we have observed in the tests to this point.

      B.B.


  5. Tom,

    Here is an odd question on this test. The “factory” barrel has had thousands of rounds shot through it. As the two new barrels are shot, it would seem that the new barrels would get smoother inside due to wear. Would this increase muzzle velocity somewhat and reduce spread of muzzle velocities at each power setting?


    • Herb,

      I have records that show the velocity of this rifle has not changed in 12 years. That’s with close to 10K shots on it.

      B.B.


  6. I scored poorly on tests for analyzing numerical data, and it’s not easy for me to keep numbers in my head. Perhaps a chart? :-) Or maybe an executive summary. :-)

    On the subject of my Enfield No. 4, I’ve looked at the problem with fresh eyes. Staring down into the breech with my best imitation of a gunsmith, I see that the rounds in trouble are not hung up so badly as I thought. The very bottom of the front end is caught; it’s a question of a millimeter. And this only happens on the right side of the stack of rounds. I notice too that the leading end of the snap cap is flat with an edge. Over time, paint has worn away so that this edge feels quite abrasive to the point of being sticky. Looking in the Lyman handbook, I see that there are various shapes for .303 rounds including round nose and spitzer all of which look like they would chamber better than mine. And feeling my Sierra Match King bullets and other rounds, all of them are much smoother than my snap caps. So, I’m guessing that the snap caps are the problem and not the rifle. I’ll get this figured out once my ammo arrives.

    Matt61


    • Matt,

      I think you’ll find that the real ammo cycles fine. Snap caps have a different balance and weight than real stuff, so they don’t react the same to being fed from the mag. They’re close, but not the same. I have the same concerns when reloading for any of my semi autos in that if the bullet profile or the balance (different weight than what the gun is designed for) is off, they don’t feed right and may jam. Or even if the pressure curve rise and fall isn’t timed correctly, it causes feeding problems. So, I imagine that the differences between snap caps and real ammo would cause problems in a fast feed bolt action too.

      /Dave


  7. Tom,
    I like that the velocity spread narrows as the power setting goes higher. I think that’s the way the Talon was meant to be in its design – for higher velocities. So, so far so good on the testing. I think the 0 setting is for those of us shooting for close up, i.e.; 10m plinking so that we don’t have to be pumping so much or tearing up our back stops. Then, when we get serious about shooting, looks like we can go straight to 6 or maybe 10 depending on how your accuracy test goes.

    I think twotalon’s comment – “velocity difference between power setting 6 and 10 why bother with 6″ -is valid in hindsight, however, accuracy will really tell which is better, so both still need to be considered. If they both come out the same at the end then I would use a 6 setting to conserve just that little bit of air.

    -Chuckj


    • Chuckj,

      I plan to test both power setting with each pellet at each distance I test. That will at least be 25 yards and 50 yards.

      B.B.


    • chuckj

      Tom and I are not looking for quite the same things here. Anything that I would want answered is strictly for my own purposes, not for everyone in general.

      I know how my Talons work, so I might not want to run them the same way that Tom does with his.
      Both of mine are ratty when running on the front side of the curve. I always set them up to start at the front edge of the top of the curve when in straight Talon mode. When I run the Talon with the Condor power plant, I start at 30f.p.s. down on the front of the curve. It does a nice curve . 30 fps climb to peak, 30 f.p.s drop to where I stop on the back side of the curve. 950 fps average for a 30 shot string (Kodiaks). 960 peak.

      twotalon


  8. I’m kind of wondering if the engineers at the factories that design the guns have already done these tests and chose the optimal twist rate in their barrels. I can’t see them just picking a number out of a hat or something and calling it good. There has to be some science involved in their barrel designs. One barrel I’d like to see tests on is an FX smooth twist barrel. I’m sure you have heard of them. They are smooth bore until the pellet hits the last few inches then it is rifled. FX says these barrels are more accurate than the walther lothar barrels. Care to test this BB?


    • John,

      First you are assumong there ARE engineers at the “factory.” In fact, there often aren’t.

      Second, the 1:16 twist was adopted in 1905 by BSA and hasn’t really changed. It’s a .22 long rifle twist.

      As for the Smooth Twist, I may get around to testing it some day, when it comes into more general use.

      B.B.


      • I’m assuming that somebody draws up the blueprints for the guns the factory turns out. I’m betting there are not mysterious little green men that come in on the new moon when the place is closed for inventory control and leave the blueprints for somebody to find then ride off on pink bunnies.

        In 1905 somebody at bsa must have done these tests and figured that was correct. But your tests are interesting to read and they do tell us things we have been asking and show us the raw facts which is always good.



  9. Well, it took me a while to comment because I had to create a table and then stare at the data for a while. I have not had time to run any t-tests, but I’m pretty certain that there would not be much there that holds up as truly being statistically different (except for one thing), given the sample size of ten on each data point – I’m not trying to be negative, that is just the world of statistical analysis. As such, I don’t put much weight on the very small drop in power on the slow twist barrel at power setting 10 . . . .

    That said, I see two things that I find of interest, even if they prove to not be statistically different:

    1) The most striking thing I observe in the data is that at the “O” power setting, the slow twist barrel produced significantly more energy on average than either the factory barrel (~25% more) and the fast twist barrel (~ 40% more) – probably enough more to be statistically significant (note also that it produced more power with both pellets when set at “6” and on one pellet when set on “10”, even though it was to a lesser degree as the energy of the shot went up). This could prove to be of value, because if stable in flight, slow twist may be the way to go with low power guns. This could be a function of energy efficiency, given that part of the energy from the powerplant goes into translational energy (speed and kinetic energy), rotational energy (rpm and angular moment energy), and entropy. Slower twist would be putting less into the rotational energy, potentially leaving more for kinetic energy, and that could explain this data. Note also that this effect is approximately linear over the three sets of samples, and looks compelling across the three sets of data points – everything fits the pattern, with the slow having the most energy per pellet type, the factory having the second most, and the fast twist having the least.

    2) Of interest (but not as compelling as above) is the relationship between consistency in ES to power level setting by twist rate. There seems to be a trend that shows that the slower twist rate barrel gets to a more stable energy level at a lower power level setting than the factory barrel does, which in turn seems would stabilize its ES a lower power stetting than the fast twist barrel does. But this is not as compelling, as it would take more data points to really tease this one out – we would need to define what “stable” means (which could vary for each barrel) and then test at more power levels to really see where the effect takes hold, since this effect does not appear to be a linear one. It is troublesome that the single worst ES data point was with the slow twist barrel, but again I doubt the difference here is statistically significant (and it may be that the stability of the powerpalnt a low energy levels is the biggest contributor at this particular test point). I’m not suggesting you go after it BB, but you asked for what we saw. I do think this could be related to the same effect as the one above – lower twist rates for lower power (or speed of projectile anyways).

    Either way, I am really looking forward to the accuracy tests . . .

    Alan in MI


    • Alan,

      Thanks for looking at the data so closely. Yes, you see what I see — the slower twist does mean the rifle operates more efficiently in the lower ranges. And it seems to develop maximum power on setting 6. If it is just as accurate at both distances as the factory barrel (and I doubt that it will be) then this twist gives you more shots per fill, because you can operate at a lower power level and use less air per shot. However, the number of shots we are talking about may only be one or two, so again, not much is gained.

      This is the sort of stuff I want to know.

      B.B.


  10. BB,

    I have a question that relates to this topic in a roundabout way. Over the years since the introduction of mass produced rifled airguns what has been the the most readly available pellet shape to consumers? The diabolo wadcutter, diabolo dome, something else? Does it vary by country? Has it changed over time? The reason I ask is because when I was a kid in the 70′s growing up in rural central North Carolina wadcutters were pretty much the only thing available unless you were near a larger city (like say Raleigh) where there might have been more of a selection in stores.

    David H


    • I suspect the wadcutter was most common in the US as most of the readily available pellet guns were probably looked upon as an upgrade from steel BBs; the guns were likely low-powered, and effective ranges were short… And not used for hunting — just plinking and target shooting (where wadcutters excel on paper, double entrendre intentional).

      Europe, where hunting class guns had a longer history, domed pellets may have been at least as common as wadcutter.


    • David H.,

      Certainly the diabolo wadcutter has been very prevalent in the U.S. but don’t overlook the Benjamin High Compression dome. There were a lot of those around when I was growing up in the 1950s.

      I suspect the wadcutter was the most prevalent, though.

      B.B.


  11. Hello BB you mentioned that the diana 27 is a great rifle,I totally agree. I recently picked up a nice one the other day. Its the model with the striker trigger and has 6/38 stamped on the butt .also t he butt is wider at the bottom than the top however it does not have DNR stamped on it I believe the mainspring is really weak , I would like to get it back to original specs but cant find much info on this particular version on the net .Could you point me to a airgun smith who could do the work? Im a little

    leary of the trigger on this one or I would do it my self .By the way its in 22 caliber .Thanks I really enjoy this blog Dennis in St Louis


    • denngos,

      Welcome to the blog!

      Your rifle is so simple that you might want to try your hand at tuning it. But either way, this man probably has the parts and can certainly do the tune for you:

      John Groenewold, PO Box 830, Mundelein, IL 60060-0830, (847) 566-2365
      http://www.jgairguns.biz

      How about a guest blog after you get her running again? We would all enjoy seeing an old classic like yours.

      B.B.


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