How does rifling twist rate affect velocity and/or accuracy? Part 10

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

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Part 8
Part 9

Today, we’ll begin looking at the effects of the rifling twist rate on the accuracy of our test AirForce Talon SS rifle in .22 caliber at 50 yards. If you’re prone to jumping to conclusions before all the data is in, I have to caution you that today’s test will look bad because I’m testing the custom barrel that has the 1:22″ rifling twist. We know from the earlier tests that this barrel was most accurate at 10 meters on power levels zero and 6. Above that power level and also out at 25 yards, the accuracy of this twist rate broke down. So, it would be reasonable to assume that this barrel will give results that are even worse at 50 yards.

That didn’t stop me from trying my hardest to shoot well. I was able to watch each pellet go into the target paper because of the distance, and that was disconcerting when the pellets landed so far from the aim point and from each other. Let’s take a look at how the rifle did.

The day was nearly perfect, as it has to be to get good accuracy from pellets at 50 yards. The air was calm, except for some light breezes from time to time. I was able to work around these breezes and get the results I was after.

I decided not to test the rifle on zero power because of the long distance to the target. Any breeze would have so much time to blow the pellets off course that I felt it wouldn’t prove anything. So, both pellets were shot on power levels 6 and 10. That’s how I’ll test all 3 barrels.

You may remember that this barrel produced velocities that were very close to each other at power levels 6 and 10. With 14.3-grain Crosman Premiers, the respective velocities were 840/854 f.p.s.; and with 15.9-grain JSB Exact Jumbos, the velocities were 817/815 f.p.s. We expect the pellets in this test to go to the same place on the target, and I would expect the two groups for each pellet to be pretty similar in size.

Crosman Premiers
I started with Crosman Premiers and the power set to 10. I did not adjust the scope since completing the 25-yard accuracy test and the center of the group landed about 3.9 inches below the aim point. Ten pellets went into a group that measures 2.04 inches between centers.

Talon SS rifle Premiers 50 yards power 10
Ten Crosman Premiers went into 2.04 inches at 50 yards on power setting 10. The center of this group was about 3.90 inches below the aim point with the scope set for 25 yards. The pellet at the top center is part of another group — not this one. I did account for the full size of the pellet on the left that just clipped the edge of the target paper.

On power setting 6, the center of the group also struck the target 3.90 inches below the aim point. These measurements of the groups are just approximate since the center of each group was difficult to locate precisely. The 10-shot group size on power setting 6 was 2.607 inches between centers. This is slightly larger than the group shot on power setting 10.

Talon SS rifle Premiers 50 yards power 6
Ten Crosman Premiers went into 2.607 inches at 50 yards on power setting 6. The pellet hole at the lower right is not part of this group.

JSB Exact Jumbo
Next, it was time to test the JSB Exact Jumbo pellet. I started with power setting 10. The center of the group landed about 4.25 inches below the aim point.

Ten pellets shot on power setting 10 went into a group that measures 2.509 inches between centers. The group is much taller than it is wide.

Talon SS rifle JSB Heavys 50 yards power 10
Ten JSB Exact Jumbo pellets went into 2.509 inches at 50 yards on power setting 10. The group is taller than it is wide for reasons unknown.

On power setting 6, the 10-shot group size was 3.222 inches between centers. This group is considerably wider than the group shot on setting 10. Why that is, I have no idea.

Talon SS rifle JSB Heavys 50 yards power 6
Ten JSB Exact Jumbo pellets went into 3.222 inches at 50 yards on power setting 6. The group is quite a bit wider than the group shot on power setting 10. I have no idea why that is.

Conclusions
As expected, neither pellet did especially well at 50 yards with the 1:22″ twist barrel. They did stay closer together than I expected, however.

The Premiers were more accurate than the JSBs, which parallels what both pellets did at 25 yards.

I don’t see any real evidence of tumbling pellets with either pellet on either power setting, so it’s too simple to say they’re just destabilizing. They’re less accurate but still stable at this distance. There’s probably something profound in that — something like the pellets still fly point-forward, but erratically. I can’t prove anything, yet, but now I have one barrel’s results in the can and it’s time to look at the factory barrel next. And that one has the twist rate that the manufacturer thinks is best for this airgun.

Final note
When I pitched the idea for this test as a feature article for Shotgun News, the editor told me he has never seen a test like this before. Neither have I. This may, in fact, be the first time anyone has published the results of testing three rifled barrels of different twist rates in the same gun under the same conditions. It probably has applications in the firearms world as well as for airguns. So, you readers may be in on something that’s being done for the first time.

We still have to test the factory barrel and the 1:12″ twist barrel at 50 yards. As a final report, I’ll summarize the entire test and the lessons I believe it teaches us.

39 Responses to “How does rifling twist rate affect velocity and/or accuracy? Part 10”

  • Gunfun1 Says:

    Not going to see the true results until all 3 barrels are tested. Are you shooting from a rest? I don’t remember if you said this before.

  • duskwight Says:

    B.B.

    Yet another great piece of a great work!

    “Tall” groups may be the result of variations in pellet weight – the longer the distance, the more it acts giving different ballistic coefficient. So a meticulous young lady (in my experience they are the best people for the task) that can spend hours weighing up pellets and grouping them into weight groups would be very helpful if some day someone would think of recreating your experiment in most mathematically pure conditions.

    I think about both groups becoming wider at setting 6 – it may be the visible result of distance-speed-rotation-stability interaction. Pellet looses speed faster, yet keeping its RPM and at some point speed/RPM proportion passes a certain point – so pellet may not tumble, but start to yaw.

    What I like most about JSBs @10 – lots of “doubles” and “triples”. So may be it’s _the_ pellet for this very barrel.

    duskwight

    • B.B. Pelletier Says:

      duskwight,

      Interesting about the weight difference. If only it weren’t with JSB pellets. I have found them to be so regular when I weighed them in the past.

      B.B.

      • duskwight Says:

        B.B.

        Even the sun has spots. I’ve read a report from a man who weighed JSBs and deviations were about .00x gram. I don’t know if that’s enough for this kind of vertical travel of POI but it exists.

        By the way, talking about JSBs and 50 m shooting. Last 3 sessions with my “shillelagh” I noticed some sudden and sharp increase in accuracy. So now I’m trying to understand the reason – is it me and some sort of skill accumulation, something got in the right place with the rifle or is it “lucky” tin of pellets. It’s not that I am against all this :) – but I’m rather intrigued if this is a coincidence that’s going to end or it’s permanent, or this is something that can be studied and reproduced.
        It’s definitel not break-in – rifle in its current state was made in 2008 with 15000 shots old.

        duskwight

        • B.B. Pelletier Says:

          Duskwight,

          Some would say the increase is due to seasoning the bore with the pellets you use. I don’t subscribe to that, but many good shooters do.

          B.B.

        • twotalon Says:

          duskwight

          You did not say if you were shooting all the same kinds of JSB pellets, or if you were shooting different kinds of the JSB. You did not say if you got the sudden improvement when starting a new tin of the same kind of pellet you had been shooting, or if it happened in the middle of a tin.
          You also did not say how many shots it took to get this sudden improvement.
          A bit more information here might help point in the right direction.

          twotalon

          • B.B. Pelletier Says:

            twotalon,

            When I link to the pellets, they are the pellets I used. If there was more than one of a certain type of pellet, there would have been multiple links.

            And the JSB Exact Jumbo is a single type of domed pellet that weighs 15.9 grains. Only one type of JSB Exact pellet was used in this and all previous tests for this series of reports.

            B.B.

          • duskwight Says:

            twotalon

            It just suddenly started in the middle of a tin, then I opened another tin (same batch) and it continued. And about shots, well, it must be some time after cleaning – some 300-350 perhaps. Thus I doubt if it’s barrel seasoning – I know this rifle too well and know the way its barrel works. It just started – I got to the range, zeroed in from 25 to 50 m and it started to send one after another waaay better than ever before.

            Now, when I thought it over, the reason may be in a pause. I didn’t shoot this particular rifle for about a month, so I am extra careful and concentrated when making shots, because I knew that I may have gotten out of habit. So, perhaps it’s just psychology.

            duskwight

            • twotalon Says:

              Sounds like it was probably you . An instant change from one session to the next while working with the same tin of pellets pretty much rules anything else out.

              Let’s say that you had been previously shooting Crosman pellets and leaded the bore. While shooting the JSB, it is possible (remotely) that a flake of leading may have broken off some time during the session and suddenly changed the accuracy. That would have been about the only off the wall thing that I could have thought of. But since this is not the case, then it is irrelevant.

              twotalon

  • Fred DPRoNJ Says:

    BB,

    just a thought I had as a result of my one time bench rest competition with rimfire. I found that the wind had different characteristics due to the terrain on the range we were shooting at. While the wind had seemed to die down at the shooting ports, it seemed to still be swirling at the target. When I shoot my air rifles back home here in New Jersey on a breezy day, I will staple a ribbon to my target backer to see what the wind is doing at the target. This way, it enabled me to be as confident as possible that the wind had completely died down and was not still blowing at the target. Not as exact as others who will employ flags along the aiming path but it’s the best I can do under the circumstances. I am curious if you employ something similar to see what the wind is doing 50 yards away from your firing position?

    Fred DPRoNJ

    • B.B. Pelletier Says:

      Fred,

      When Edith competed in BRV (a benchrest target match of precision) she used wind flags.

      I don’t use them because I shoot on a bermed range. If I feel the wind it’s there and if I don’t, it’s not.

      B.B.

    • Desertdweller Says:

      Our shooting range uses a single tall berm as a backstop. The rest of the range is open to the wind.

      I installed a tall post with a ribbon on top in line with the target frames. I find it to be helpful.

      We have a tall flagpole near the 100 yard bench for flying the red range flag. That was too far from the target line, and nowhere near the shooter’s line of sight to be very helpful for judging wind.

      Les

    • Victor Says:

      Fred,

      Most competition ranges that I’ve shot at had flags at both 50 yards and 100 yards. In addition to this, most shooters had some kind of windmill/wind indicator at their shooting position (which I think is less useful than the flags).

      What you’re doing should work, provided that you practice using it to better understand what it’s telling you in relation to how the bullet/pellet is being affected by wind. For informal shooting, I use strips of cloth that I hang off to the side of my target holder frames.

      For wind-doping, the things that matter are; wind direction, wind speed, temperature (in hot weather you can read the mirage), and of course the direction of the rifling in your guns barrel. For my Anschutz rifles, wind from the left moved the point of impact to the right and low, while wind from the right moved it to the left and up. So wind doesn’t just move the point of impact in its direction, it actually moves the point of impact diagonally.

      Also, you usually have less wind early morning, and it increases throughout the day. That’s why in small-bore prone matches you start off with the Dewar match (20 rounds at 50 yards, followed by 20 rounds at 100 yards), then the 100 yard match (40 shots). By late morning, early afternoon, you’re shooting at the closer distances of 50 meters, and finally 50 yards.

      I would advise the range to put wind flags at the distances shot for competition. Without some indication of what the wind is doing, you’ve just added a huge random variable, I think.

      Victor

      • Matt61 Says:

        Isn’t this deflection high and low from sidewinds an example of the Magnus Effect? We talked about that here a long time ago.

        Matt61

        • Victor Says:

          Matt61,

          Yes, that’s exactly what it is. I say diagonal, but it isn’t exactly linear. This is far from being theory, when shooting small-bore matches, where you shoot 160 shots, plus probably another 40 to 80 sighter shots, you clearly see this effect quite often.

          In precision class competitive marksmanship, you are discouraged from using Kentucky Windage (i.e., aiming off center to account for wind), but instead are suppose to go to your “sighter bull” to test and adjust your sights accordingly. A variation of this is to sight in your rifle to the edge of the 10 ring, or X ring (tie-breaker), on the side in which the wind is blowing from. I believe this is called “shaving”.

          It’s interesting to see how this affects shooters who “shave”, versus those that don’t. Shooters that don’t, and are highly picky about their sight adjustments and tend to get very high X-counts, but will drop points on occasion (one, maybe 2) because they get caught off-guard when the wind changes. Shooters who shave, will have a lower X-count, but are less likely to drop points.

          Victor

        • Victor Says:

          Matt,

          I’m not convinced that the Magnus effect applies so much with pellets. I may be wrong, and maybe it applies more, but I can’t say because wind affects pellets a lot worse than bullets in my experience.
          I can dope wind with bullets, but I haven’t figured out wind doping with pellets. I just haven’t seen predictable behavior with pellets.

          But remember, pellets use a skirt for stability, just like a “birdie”. My guess is that wind changes their direction (orientation) in a way very different from a bullet, and that could make all the difference in the world.

          Victor

  • JGC Says:

    B.B.,

    Sorry for the new topic break in…

    After giving the Benjamin 422 the PelGun Oil treatment, the next stage of the project was to find a suitable pellet for semi auto operation.

    Drum roll…

    (Sorry about the theatrics)

    H&N Sport Field Target Trophy 14.66 grain round nose.

    Yes, I know that this pellet is heavy for the pistol, but it is hard to pass up 10 shots with no misfires/multiple pellet burps, (MPBs) etc.

  • Matt61 Says:

    Hm, well I wasn’t placing my bets on a 1:22 barrel… If the pellet from these barrels is less accurate while still stable can you just attribute it to the lack of spin which we know makes pellets more accurate? :-)

    Matt

  • GenghisJan Says:

    I’m excited. It’s been about three years since I treated myself to a new airgun. I just ended this dry spell by ordering an old Walther LGR Universal.

    I have this fantasy that I will practice my offhand in the basement using the match sights. But I wonder how long I’ll go before scoping it and dragging it to a DIFTA match…

    Woohoo!

    -Jan

    • Titus Groan Says:

      Congratulations Genghis. It’s always a great feeling you get from the time you ordering the gun, until having it finally show up at your door. Then the real fun can begin. Just because the Walther LGR you bought isn’t new, the excitement of that first glimpse of your new gun, is just as intoxicating as if it were. As I peruse YT, there seems to be quite a proliferation of un boxing airgun videos. I suppose we can attribute the emotion we feel watching someone revealing their new airgun purchase, as being universal in it’s appeal. Maybe I can convince my daughter to write a paper about this effect for her masters theseus. Or maybe it just isn’t that important.
      What is important, is the news one of the major on-line importers of airguns in Canada, is selling the Air Arms TX200 in under 500fps configuration for us Canucks who don’t have a PAL certificate.
      Some might argue that such a gun would not perform as the winning springer it is in 12+flbs. configuration, if it is detuned to comply with Canadian gun laws. I have never thought of the possible effects of this, until I wrote this down. Might be an interesting experiment. I guess I will have to buy the TX200 to find the answer. Should be a good enough excuse to tell my wife why I need another airgun, regardless.
      Matt, I have been observing amateur camera video of the conflict in Syria. This is video taken by the actual combatants of the civil unrest. There seems to be a lot of horrific atrocities being perpetrated by both sides. I would expect there would be more from a rebel army simply because they haven’t been trained, and are not as disciplined. However , it seems both sides delight in the torment of prisoners, and civilians alike. Being a family oriented blog, I will not go into detail. Besides, everything I talk about is readily available on YT. I suppose war brings out the best and the worst in humanity. When I think of how I am able to watch un edited footage of a historical event unfold, it really puts the World Wide Web in focus. It also shows how the WWW can be used for propaganda purposes by anyone with an agenda.
      Caio Titus

  • GenghisJan Says:

    I’m chiming in VERY late on this fascinating series. B.B., since you have so much free time, I wonder if the slower- and faster-twist barrels might shine with more extreme ammo and velocity choices. E.g., maybe the 1:22″ would work well at higher velocities that we might usually avoid? And/or perhaps extremely long or short pellets would be worth trying?

    Maybe try the 1:22″ with something long like a Eun Jin, lobbed as fast as you can with a condor tank??? See above about your copious free time…

    Thanks,
    Jan

    • B.B. Pelletier Says:

      Jan,

      We know that longer pellets and bullets need a faster spin, not a slower one. So unless I could launch the Eun Jin at 1100 f.p.s., which the 12-inch barrel will never do– I’m afraid it won’t work.

      B.B.

  • Gunfun1 Says:

    BB kind of off topic. But did you get a chance to do that test with the 3 different length barrels with the same power plant and twist rate that we talked about before?

    • B.B. Pelletier Says:

      Gunfun1,

      No, that test has to come after this one ends in July. I am under the gun to shoot the other 2 barrels at 50 yards to finish not only the blog report but also a feature article for the September Shotgun News that is on the same topic.

      Then I will do the other test you requested.

      B.B.

  • Gunfun1 Says:

    Also forgot. On this test with the different twist rate barrels. I know you want to keep the test the same on all barrels so you are using power levels 6 and 10.
    But on this barrel (1:22″ twist) do you think the accuracy would of improved with more power to get the fps faster?

    • B.B. Pelletier Says:

      GF1,

      The 1:22″ barrel won’t go any faster! It peaks out on power setting 6. See the report on that.

      B.B.

  • Gunfun1 Says:

    Hitting the send button to quick today.

    I know what happened at 25yrds. But just wondered if you gave it a try with the higher power at 50 yrds. Just for the fact that sometimes surprises happen.

  • Gunfun1 Says:

    BB thanks for the reply.
    Do you ever get a chance to relax?

    And Ok that is something to remember about the 1:22″ barrel. Velocity is at its maximum.

  • Lumjack Says:

    Mr.BB im trying to decide which is a better. Quality, the patriot,webley sting ray or the cometa 400 all in. 22cal

    • B.B. Pelletier Says:

      Lumjack,

      Which tastes better, Coke or Pepsi?

      I’m saying that I can’t ask a question that hasn’t been asked. The three rifle you asked about are all very similar. Had you included the RWS Diana 34, there would have been a clear choice — the Diana.

      The Patriot is a Hatsan, as is the Stingray. The Cometa 400 is different but in the same build category as the other 2.

      But the Diana 34 trumps them all, in my opinion.

      B.B.

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