How does rifling twist rate affect velocity and/or accuracy? Part 2

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

Part 1

Let’s begin our look at the effects of the rifling twist rate on accuracy and velocity. This will be a huge test. I know many of you will want to know THE ANSWER sooner than I get to it. All I can do is ask you to be patient because this has never been documented for the public, if indeed, it has even been done before.

We’re testing the 1:22″ twist barrel that Dennis Quackenbush made for the Talon SS test rifle. I’ll use the velocity figures that I recorded for the factory barrel several months ago in the 10-part Talon SS report. After I’ve tested the 1:10″ twist barrel (in the next report), I’ll also retest the factory barrel following the exact test structure I’m using for both Quackenbush barrels. I know my rifle very well and don’t expect the numbers to be that far off. So, you can accept today’s figures as gospel, but I’ll retest the gun just to make sure.

I followed a fill process that’s very exacting, so each test is the same as all others. I’m not going to bore you with the minutiae, but I discovered while testing the gun on the lowest power setting that the velocity climbed after about 5 shots immediately after a fill, so I refilled the reservoir after each test on low power. On the higher powers, the gun is very stable across the useful fill, so those tests did not all begin at 3,000 psi. They were tested with 2,600 psi to 2,800 psi in the air reservoir — a range where the velocity is extremely regular.

I’m going to use only two pellets initially. Until I learn something about the performance of these barrels, it’s not worth spending endless time running down “facts” that don’t really matter. Later, if the data indicate a need for expanded testing, there will be additional velocity tests with other pellets.

The best way to view the results is when they’re grouped by power setting. Each pellet was tested with the rifle set at three different power settings. Since my gun doesn’t have a scale on the power adjustment window, I put a piece of tape there and marked it for the two higher power settings. The lowest setting is with the power screw indicator as far to the left as the window permits.

Talon SS power settings
Tape marks the two higher power settings. When the screw head is centered on the index mark, the power is correct. When the screw head is as far to the left in the window as it will go, the power is on the lowest setting.

Power setting 0

Factory barrel
On zero power with the factory barrel, 14.3-grain Crosman Premier pellets averaged 486 f.p.s. the range was from 451 to 522 f.p.s. That is an average energy of 7.5 foot-pounds.

On zero power, 15.9-grain JSB Exact pellets averaged 507 f.p.s. The range went from 498 to 521 f.p.s. At the average velocity, this pellet produces 9.08 foot-pounds on this power setting. And the spread is 23 f.p.s.

The velocity spread for both pellets is on the high side, with Premiers being the highest at 71 f.p.s. That tells us the valve is not too stable at the lowest power level and a full fill of air.

1:22 barrel
On zero power with the 1:22 barrel, Crosman Premier pellets averaged 534 f.p.s. The spread went from 499 to 569 f.p.s. — a range of 70 f.p.s. At the average velocity, this pellet produces 9.08 foot-pounds of muzzle energy.

On zero power with the 1:22 barrel, the JSB Exact pellet averaged 521 f.p.s., with a range from 482 to 528 f.p.s. That’s a spread of 46 f.p.s. At the average velocity, this pellet generated 9.59 foot-pounds of energy.

Again, there was a high velocity spread for the Premier pellets, and the JSBs were tighter. With both pellets, the muzzle energy increased with the 1:22″ twist over the factory barrel.

Power setting 6

Factory barrel
On setting 6, the Crosman Premier pellets averaged 787 f.p.s. from the factory barrel. The range was from 775 to 800 f.p.s., so the spread was a tighter 25 f.p.s. At the average velocity, this pellet generated 19.67 foot-pounds of energy.

On the same setting, the JSB Exact pellets averaged 778 f.p.s. with the factory barrel. The range was from 769 to 785 f.p.s., so the spread was 16 f.p.s. At the average velocity, this pellet generated 20.57 foot-pounds of energy.

1:22 barrel
The Crosman Premier pellets averaged 840 f.p.s. from the 1:22 barrel on power setting 6. The range was from 831 to 847 f.p.s., so the spread was a much tighter 16 f.p.s. At the average velocity, this pellet generated 22.41 foot-pounds of energy.

On setting 6, the JSB Exact pellets averaged 817 f.p.s. from the 1:22 barrel. The spread went from 810 to 824 f.p.s. At the average velocity, the energy generated at the muzzle was 23.57 foot-pounds.

Power setting 6 boosted the power a lot. It also stabilized the velocity quite a bit with both pellets. As you can see, the 1:22″ barrel outperformed the factory barrel by quite a lot. This is especially noticeable when you look at the muzzle energy.

Power setting 10

Factory barrel
The Crosman Premier pellets averaged 854 f.p.s. from the factory barrel on power setting 10. The range was from 850 to 860 f.p.s., so the spread was a very tight 10 f.p.s. At the average velocity, this pellet generated 23.16 foot-pounds of energy.

On setting 10, the JSB Exact pellets averaged 823 f.p.s. with the factory barrel. The spread went from 821 to 825 f.p.s., which is just 4 f.p.s. At the average velocity, the energy generated at the muzzle was 23.92 foot-pounds.

1:22 barrel
Crosman Premier pellets averaged 854 f.p.s. from the 1:22 barrel on setting 10 — the identical speed they got with the factory barrel on this setting. The range was from 844 to 863 f.p.s. Although the average was the same as for the factory barrel, the spread was much greater at 19 f.p.s. At the average velocity, this pellet generated 23.16 foot-pounds of energy.

On setting 10, the JSB Exact pellets averaged 815 f.p.s. from the 1:22 barrel. That is LESS than it was on power setting 6. The spread went from 809 to 819 f.p.s. At the average velocity, the energy generated at the muzzle was 23.46 foot-pounds.

Power setting 10 is as high as I ever run my Talon SS. I haver determined that with a 12-inch barrel any setting above this one just wastes air. While the velocities may be a little different with the different twist rates, I believe the general rule will hold that setting 10 is as high as any 12-inch .22-caliber barrel wants to go — at least with the powerplant on my rifle.

The results of this test
As you can see from these results, the gun is wasting air on power setting 10 with the 1:22 twist rate. It is much more efficient on power setting 6. And it does not give up any power to the factory barrel, leading me to wonder if a 1:22″ twist rate might not be a better rate for .22-caliber pellets in the middle power range.

The factory barrel edged out the barrel with a slower twist by getting 23.92 foot-pounds of energy from JSB pellets on power setting 10 compared to 23.57 foot-pounds with the 1:22″ barrel shooting JSB pellets on power setting 6. I don’t know what that says, but there it is.

We’ve learned a little from this test, and we now know there’s so much more to be explored. The results were not as dramatic as some might have anticipated. Many thought the slower 1:22″ twist would have sped up the pellets noticeably, but that didn’t happen. What it did seem to do was make the rifle more efficient in the middle range of power.

It’ll be interesting to see what the 1:12″ barrel does under the same circumstances. After that, I’ll retest the factory barrel at these test settings to verify they’re correct.

36 Responses to “How does rifling twist rate affect velocity and/or accuracy? Part 2”

  • Alan in MI Says:

    Interesting results! I’m glad that you are into this test – I am really to looking forward to seeing how it progresses.

    Just curious since I didn’t catch it in the report – how many pellets were you shooting for the spread and average speed at each setting?

    Alan in MI

    • B.B. Pelletier Says:

      Alan,

      I shot 10 in each string. That has gotten so standard that I forget to put it in print anymore.

      Sorry,

      B.B.

  • kevin Says:

    At power setting 10 the velocity out of the 1:22 barrel was the same with premiers and less with jsb pellets? I’m having a hard time wrapping my head around this.

    kevin

  • kevin Says:

    For clarification I meant to say, At power setting 10 the velocity out of the 1:22 barrel was the same with premiers and less with jsb pellets WHEN COMPARED TO POWER SETTING 6? I’m having a hard time wrapping my head around this.

    This is really shortcircuiting my little brain.

    kevin

    • B.B. Pelletier Says:

      Kevin,

      The next test will be the same one, but with the 1:12 barrel. That should give a lot more definition to the data — I hope! After that I verify the Factory barrel velocities and the body of data will be completed for this part of the test.

      I hope to put these data into some kind of graphic presentation, so we can see them all as they compare to each other. Maybe when that is done the thing will start to make sense.

      B.B.

      • Wulfraed Says:

        I’d still want to take the velocity differences out of the picture — that would mean tweaking the power adjustment between barrels to put any give pellet into the same velocity across the barrels (or, at least, same “mean” via statistical acceptance [would this be a two-sampled t-test of baseline barrel vs alternate barrel -- actually, probable need three tests as base-fast and base-slow may both pass, but fast-slow be out])…

  • twotalon Says:

    GenghisJan….

    Rear sight…slides over the rear dovetail.
    http://i189.photobucket.com/albums/z244/twotalon/004-2.jpg

    Front sight…sight fits in the dovetail on the thing. The thing can be removed with a 2mm allen.
    http://i189.photobucket.com/albums/z244/twotalon/001-4.jpg

    Power adjust…remove screw with 2mm allen. It’s just a cap. The adjust is a 1.5 mm screw under it.
    http://i189.photobucket.com/albums/z244/twotalon/002-1.jpg

    twotalon

    • GenghisJan Says:

      Thanks, TT! The T200 seems like it could make for a great upgrade from my Disco’ as a lightweight iron-sights-capable rifle that my kids could use.

      Too bad the ‘T’ model is (presumably) not available in the red laminate stock that my kids think looks cool… ;)

      Thanks,
      Jan

      • twotalon Says:

        Jan …

        A few things I should mention…

        The included sight inserts could have had more variety.
        The included tool kit does not have ALL of the allen wrenches needed, but has most.
        You will probably need an adapter for the included fill adapter. PA does carry the part.
        The bleeder is right on the included fill adapter.

        I am very happy with mine, except for an original problem with a horrible barrel.
        I got a different set of sight inserts from Brownells that work, but fit really tight. The originals fit tight too.

        twotalon

      • twotalon Says:

        Forgot…too early….

        There are four o-rings included. Two for the bolt, and two for the air tank. Love having spares.
        Metric of course. Must be a Euro conspiracy of some kind.

        twotalon

        • GenghisJan Says:

          Thanks for all the info, twotalon! I had no idea they came with o-ring spares. Very nice touch.

          -Jan

          • twotalon Says:

            Jan..

            It would not surprise me to see PA drop this one for lack of sales.
            Not cheap or expensive enough, or not enough power.
            It would be a shame, really…..
            You can crank it up if you want, you get a built in air guage, target sights included, and less expensive than the standard S200.

            twotalon

  • Fred DPRoNJ Says:

    BB,

    while I’m still working with my Talon SS I purchased at Roanoke this year, I can verify your results at power setting 6 – that is, they are almost identical to my results in my exploration of what the rifle can do. That’s with the stock, shrouded barrel.

    Fred DPRoNJ

  • Herb Says:

    RE quot: “Many thought the slower 1:22″ twist would have sped up the pellets noticeably”

    Why would a slower twist make pellets speed up?!?

    • B.B. Pelletier Says:

      Herb,

      They believe that a faster twist introduces greater friction. That’s probably not exactly correct, but greater resistance.

      B.B.

      • Victor Says:

        B.B.,

        That makes sense to me too, and obviously especially during the initial thrust. I’d imagine that as the pellet moves further down the barrel its spin gets closer to matching the twist rate. But by then, it’s slowed down more significantly from it’s initial velocity.

        The question is, how much potential damage might there be to the pellet, because of the unmatched cut made by the rifling, if any?

        I wonder if more pressure is lost when shooting a pellet at too high a velocity through a barrel with too high a twist rate because of excess cutting by the rifling, if any?

        By “matched”, I’m referring to how ideal the velocity versus twist-rate is, such that the pellet begins to spin with minimal friction because its spin is equal to the twist rate. All rifles will cause a certain amount of friction due to acceleration of spin between the time the gun fires and the time the pellet begins to spin with the rifling.

        Victor

        • B.B. Pelletier Says:

          Victor,

          The recovery of numerous lead pellets and bullets proves conclusively that there is ZERO difference between the pellet’s spin and the twist of the rifling. If there was any, the pellet or bullet would be said to be stripping in the lands. That doesn’t happen at normal velocities.

          B.B.

          • Victor Says:

            B.B.,

            I understand. From a practical standpoint what you say makes sense. I’m somewhat influenced by mathematical modeling work that I did back in the mid-80′s where we had to analyze seemingly insignificant responses to things, including ramp and transient analysis.

            Victor

  • rjpura66 Says:

    Have you ever explored FX’s smooth twist barrel?From what they state it is a smooth bore from breech to a few inches from the muzzle,then a rifling at the end of muzzle which is supposed to increase muzzle velocity while pellet is in the bore and then enough twist to make projectile stable and increases accuracy!btw 24″ barrel blanks are available in .22 and .25 at AofA website for $220 ouch!!!

  • Victor Says:

    OFF TOPIC. SORRY!

    Regarding the Ruger Air Hawk that was cleaned with gun solvent, I cleaned it thoroughly last night.
    Before I apply Pellgun Oil on that seal that I think has gone bad, I was wondering if maybe it would be better to flip the seal over. Does anyone know a good way to remove a seal without damaging it?

    Thanks,
    Victor

    • B.B. Pelletier Says:

      Victor,

      That depends on how the seal is attached. Since you think you can flip it over it can’t be a seal that only fits the piston head one way.

      So if it attached with a screw?

      B.B.

      • Victor Says:

        B.B.,

        I guess I’m not talking about a seal, and really talking about an O-ring. However, that’s not to say that there isn’t a problem with the “seal” that you’re thinking of. I haven’t looked that deeply into this.

        Victor

    • Vince Says:

      If you’re talking about the breech seal, just pop it out with a pic or a small screwdriver. It shouldn’t be held in with anything except friction.

      The piston seal cannot be flipped.

    • twotalon Says:

      Victor..

      Your best chance is to use a safety pin or something similar. Try to push the point down between the seal and the metal, then try to pry it up. Keep moving around it, working a little at a time.

      twotalon

    • Victor Says:

      I am referring to the O-ring at the breach, around where you insert the pellet. Looking at this ring, I see that it is mostly within the circular slot that it inserts into, so I would have to pick it out somehow. I was concerned that picking it out with something like a paper clip might damage it. I do have a set of tiny screwdrivers. That will probably be my best bet.

      Before I cleaned the barrel I wiped down the breach area with mild warm soap per Vince’s suggestion. I did in fact find traces of what looked like gun solvent (e.g., Hoppe’s 9). I cleaned the barrel with both JB Bore Paste and the cleaning solution from my Gamo airgun cleaning kit. After almost a couple of hours, the final dry patch came out clean.

      General question: What kind of airgun barrel cleaning solution is recommended? Is there a generic chemical I can use, or maybe a preferred name-brand product?

      Thanks so much for all of your help!
      Victor

      • Vince Says:

        JB paste seems to be harmless to seals, and since it’s not liquid it’s not likely to run into places where you don’t want it.

        But generally speaking it’s only needed in more extreme cases. When combined with a brass or bronze brush (for steel barrels only) it’s good for removing corrosion and even tiny burs. Otherwise, I’ve generally found that patches wet with common solvents like mineral spirits seem to be adequate.

        • Victor Says:

          Vince,

          Are mineral spirits what you use to clean your airgun barrels? Any particular brand? The only thing I’ve used is what comes with the Gamo kit, and I have no idea what solution they are using.

          Victor

          • Vince Says:

            Well, I’ve used paint thinner… you have to remember that for the most part there’s not much in an airgun barrel that needs to be cleaned out.

  • duskwight Says:

    B.B.

    Cannot wait for the next part of this report! For now it is quite in line with my purely theoretical musings. I also wish there was an accuracy test together with speed-energy tests – as it may be more energy with less stabilization in middle-range.

    Drilling brought some surprises – well, that’s what I’ve been given my hands for, I must rework my grip a bit and give it a little bigger angle than 90. Bushings will arrive tomorrow (part makers, again… sigh) and I hope that this time nothing will stop me from assembling all this bloody set of metalware and plywood together for a test.
    Yesterday I got 2 more 7075 uppers for DWR Mk1 – basically the same but lighter than the original. As it is one of the most difficult parts of the rifle, it means I’ve got a good field of experiment. I plan to transit from TD to Mk1 with a _significant_ loss in weight.

    duskwight

    • B.B. Pelletier Says:

      duskwight,

      There will be an accuracy test, of course. While I will not chronograph as I shoot, I guarantee you that the velocity doesn’t vary that much for a given pellet at a given setting.

  • B.B. Pelletier Says:

    Ray sent this to the wrong address, so I have posted it here for him.

    B.B. I saw your July 12 note to Don offering to send the owner’s manual for the Plainsman 175 CO2 Pistol. I sure would like to get a copy of that manual if you wouldn’t mind forwarding to me in an email. I have one of these guns sitting in my sock drawer at home. I’ve just learned that the 8mm seltzer CO2 cartridges will fit this gun. I think I want to try it out again. Thank You.

    RAY

    • B.B. Pelletier Says:

      Ray,

      I sent that document close to a year ago, as I remember it. Anyway, it will take me some time to find it. It’s not stored in any current documents, because there is no demand for it.

      B.B.

  • Matt61 Says:

    Wow, this test has a lot of variables. My first concern is that velocity and accuracy are coupled together. Presumably accuracy would increase with velocity up to a certain point and then fall off. Or there might be all sorts of different relationships. But if velocity and accuracy directly affect each other through stabilization or something else, then a comparison with twist rate gets compromised. As an extension of the same point, if firearms are an analogy, what you’re looking for is some sweet spot value that matches velocity/accuracy with a particular twist rate. So the relationship of twist rate to velocity/accuracy outside of that range is not really relevant to performance.

    I’m trying to extract the mechanical principles from the data. The choice of twist rate balances two opposite effects. On the one hand, the friction of the pellet against the rifling retards its motion for a variety of reasons. On the other hand, the rifling imparts spin to the projectile to stabilize and increase range and accuracy. Is that right?

    Kevin, I was kidding around about the wheeler and dealer part. I can see the advantages of inspecting in person. However, I don’t know if I have enough knowledge to learn anything unless the gun is complete junk.

    Wulfraed, I’ll say again, how do you know all this stuff? I wasn’t questioning the exact operation of the double-action pistols but wondering why they are designed as they are since the single-action seems to offer advantages. But that question could be changed in all sorts of ways by all the info you gave which I only dimly understand.

    Slinging Lead, thanks for the info on the S200 which I’d forgotten. I thought that B.B. got his test guns from PA, not Air Arms. As for the Japanese, I’ve heard of Edward Demmings. As an additional irony, I understand that the Detroit auto manufacturers had rejected his ideas before he sent them to the Japanese. That certainly came back to bite them. It’s a further irony that the Japanese were so eager to adopt Demmings’ ideas since their cultural disposition is very hierarchical. One pattern in WWII was that their defeats were caused by poor management skills as much as by other circumstances. Their operations were overplanned or underplanned, unresponsive to change, and the different branches of their military were fighting each other as much as the enemy. But they turned that around. And it is another trait of their culture that insular as they appear to be, they have been equally as good at adopting things that they have found useful and making them distinctively their own. There is plenty of evidence of that from the very beginnings of their culture when it separated from China around 800A.D.

    Matt61

    • Wulfraed Says:

      Wulfraed, I’ll say again, how do you know all this stuff? I wasn’t questioning the exact operation of the double-action pistols but wondering why they are designed as they are since the single-action seems to offer advantages. But that question could be changed in all sorts of ways by all the info you gave which I only dimly understand.

      Well… besides owning various firearms for over 30 years?

      A single-action semi, pretty much by definition, has an external hammer. Much of the populace would be alarmed at seeing a cocked hammer on a holstered gun (most of them don’t understand safeties, for one thing).

      Cocked&Locked carry also means the hammer spring is compressed (consider all the warnings about leaving a spring-piston air gun cocked for hours).

      A Series-80 m1911 actually has four (five?) separate safety systems: Hammer locking manual safety, a half-cock notch meant to catch the hammer if it slips off the sear, a grip safety (does this block the trigger — I’m not sure), an inertial firing pin (requires high velocity hammer fall so inertia carries the pin into the primer — if the hammer were down on the firing pin, hitting the hammer with, uhm, a hammer won’t drive the pin — and the pin is short so it doesn’t protrude into the breeech with the hammer down), and on the S-80, a trigger activated firing pin block (keeps the firing pin from moving unless the trigger is pressed back; so inertia, if the gun were dropped on the muzzle, won’t fire it).

      Granted, the Series-80 is an excessive design, in a way, three of those safeties are to prevent the gun from firing unless someone has gripped it and pulled the trigger (the real purpose of a safety). The half-cock is a safety only in that it attempts to prevent the gun from firing if the hammer/sear has malfunctioned (slipped), and the inertial firing pin is protection against impacts when the hammer is carried down on a live round.

      Advantage: consistent light trigger pull
      Disadvantage: spring compression wear, scaring the public in Cocked&Locked (or worse Cocked&Unlocked), having to manually cock the hammer is carried in uncocked mode.

      Traditional DA/SA semi-auto. Most of these use a decocker type safety. Those with external hammers typically also incorporate hammer block into the safety — they interpose a piece of metal that prevents the hammer from touching the firing pin, and then drop the hammer onto the block. Prevents the need for an inertial firing pin (and the need to balance the mass of the pin against the return spring so that hammer can impart enough momentum for the pin to hit the primer — DA/SA firing pin can be long enough that if the hammer is down on it it will be touching the primer). Striker-fired models may only have the decocker, and no manual safety position (the decocker blocks the firing pin, drops the striker, then releases the firing pin).

      Safeties on DA/SA: While technically not required they may have inerial firing pins. Decocker – always, if an external hammer model it will likely also be a hammer blocking design. Most incorporate a firing pin block actuated by the trigger. Externals will likely have a half-cock notch.

      Advantage: (especially for striker models with no manual safety) gun is immediately available for firing via double-action trigger pull, while having the lighter single-action pull available.
      Disadvantage: the transition from double-action first shot to single-action follow-up trigger.
      Draw: for external hammer models, having to release the safety first (which has to be done for the cocked&locked single-action semi too)

      Double-Action Only semi: No manual safety/decocker — the trigger pull is always the full double-action pull. Safety would be a trigger actuated firing-pin block.

      Advantage: consistent trigger pull, no complications about hammer/safety configuration
      Disadvantage: heavy trigger pull

      Some models (of any type) have a magazine disconnect “safety”… I don’t consider that a safety — it’s closer to a personalization feature: if one fears they are about to lose the weapon to an assailant, pressing the magazine release to drop the magazine results in disconnecting the trigger from the sear — so the assailant can’t fire the round in the chamber.

      Except for manual safeties, safeties only prevent the gun from firing if one has not gripped it and pulled the trigger — that is, they guard against impacts, drops, and snags (hammer slipping from thumb when cocking, for example). Manual safeties, magazine disconnects, and the pipe-dreams of New York and California (ie; having some sort of electronic or magnetic anti-use system embedded into the gun that requires having a “key” ring in just the right position or a fingerprint reader in the grip) are all things that get in the way of being able to fire a gun when you deliberately wanted to fire it by pulling the trigger — remember to release the manual safety, make sure the magazine is all the way in (, make sure your key ring is on your finger, not rotated out of alignment — and hope you don’t have to switch hands during the fight).

  • Herb Says:

    Occurred to me that a small difference between the factory barrel and the custom barrels is that the lengths are slightly different. Longer barrel will have more velocity in PCP. This won’t make up all the difference but a bit of it.

    We also don’t know exact measurements of the lands and grooves. How wide is a land and how high above the groove?

    How was breach end of barrel “prepared” for pellet? It seems you need a slight countersink to get the skirt to seat properly.

    It wouldn’t seem that muzzle velocity would be effected by the crown, but the crown would certainly be a factor in group size.

    The mating of pellet, power plant, and barrel is so intricate that the effects of all these variations are hard to predict. All in all there are more differences between the factory barrel and the 1:22 barrel than just the twist rate.

    Herb

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