How does rifling twist rate affect velocity and/or accuracy? Part 8

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

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

Today, I’m presenting the first part of the data collected thus far in this extensive test. My thanks to blog reader Fred DPRoNJ (Democratic People’s Republik of New Jersey) for creating the original spreadsheet for this data. Although I didn’t use his spreadsheet in the publication, I did use it as my worksheet to put this report together. Thanks, Fred!

This is a look at how the twist rate of rifling affects the velocity and accuracy of pellets in an AirForce Talon SS rifle in .22 caliber. We’re testing the same 2 pellets in each of 3 different barrels in the same gun. All 3 barrels are the same 12-inch length. Two of the barrels were custom-made by big bore airgun designer/maker Dennis Quackenbush for this test, and the other barrel is a factory Lothar Walther barrel that comes with the rifle. I chose this airgun for two reasons. First, it allows the quick barrel change that makes this test possible. Second, it has adjustable power so we can vary the power for each pellet we test.

I’m testing the rifle with 2 pellets. The first is the 14.3-grain Crosman Premier that has long been established as one of the most accurate pellets for a .22-caliber Talon SS. The second pellet is the 15.9-grain JSB Exact pellet that I’ve found will sometimes exceed the Premier for accuracy. I don’t believe there’s another pellet in the world that can match either pellet’s performance in my .22-caliber Talon SS.

Velocity first
Velocity was the first thing I tested, and it will be the only thing I report today. There’s too much data in this test to dump it all in a single report, so the accuracy portion of the test will follow tomorrow.

I shot 10 shots with each pellet at each of 3 different power settings on the gun — zero power (as low as the gun will go), power setting 6 and power setting 10. That was done in each of the 3 barrels, so there are a total of 18 outcomes to this test. Those 18 outcomes are shown in the table below.

My Talon SS doesn’t have a power setting scale etched on it, so I put a piece of tape on the side of the gun above the power window. Zero power is with the power-indicating Allen screw head all the way to the left in the window (the same as it would be on a gun that has an index etched on it). I put marks on the tape where power settings 6 and 10 are. I’ve tested many hundreds of these guns over the years that I know where the power screw head has to be, so these settings are quite accurate. The fact that I used the marks for each test (by centering the screw head on the mark) means that everything was identical for each test.

Talon SS power settings
The power settings were the same for every test.

Talon SS velocity table for rifling twist effect

General observations
First, I note that in all cases the velocity increased the most between power setting zero and setting 6. The velocity increase from setting 6 to setting 10 was always smaller than the increase from setting zero to setting 6, and that’s irrespective of the twist rate or which pellet was shot.

It’s true that there’s more variation between power setting zero and power setting 6 than between settings 6 and 10, but what you’re seeing here is the slowing down of the rate of velocity increase. That becomes clear in a moment when I discuss the rifle’s maximum velocity potential.

Next, I noted that, as the twist rate slowed (1:22″ is slower than 1:12″), the velocity increased at most power settings with most pellets. There was one instance with the 1:22″ barrel where the 15.9-grain JSB Exact pellet actually went 2 f.p.s. slower at setting 10 than at setting 6, but with all other barrels and all pellets, there was always a velocity increase as the power setting went higher.

Focusing on the 1:22″ barrel for a moment, we see that the velocity increases between setting 6 and setting 10 were not as great as they were in either the factory (1:16″) barrel or the 1:12″ barrel. This suggests what we have suspected all along — that the twist rate of the barrel does slow down the pellet as it gets tighter. And we can see from this test that the phenomenon is most apparent at the lower power settings. At the higher power settings, the differences seem to shrink, indicating that the influence of the power setting is overriding the influence of the twist rate. I believe this is an important finding, and it sets up the next observation, which is that the top velocity of the gun was fairly close for all 3 barrels, regardless of the twist rate. The type of pellet made more difference to the top velocity than the barrel twist rate did.

Specific things we learn from this test
It should be obvious from these results that the Talon SS powerplant has upper limits that cannot be exceeded by forcing more compressed air through the barrel. Better than anything I’ve seen, this illustrates the relationship between barrel length and velocity in a pneumatic airgun. Last week, I had an inquiry from a budding inventor who wanted to know the fastest pellet velocity I had ever witnessed. After I told him what it was, he told me he was working on an airgun design that used compressed gas at 5,000 to 6,000 psi, implying that this would increase the velocity. He told me that he had done extensive research on the internet and was unable to find anything on this topic, despite several of my own reports that address this very thing.

My point is that I get such inquiries all the time from people who are not yet connected to the airgun community and are out there reinventing the wheel. They’re working on a supposition that we all recognize as erroneous — namely that higher reservoir pressure gives higher velocity — but they haven’t gotten far enough into the subject to know that yet. This test serves as a foundation for why we say that barrel length affects velocity in a pneumatic gun.

A second thing that I found interesting is that power setting 6 is very close in performance to power setting 10. In the case of the 1:22″ twist barrel, it’s remarkably close…but it’s close for all three barrels. A prudent airgunner might consider this when setting the power wheel adjustment on his Talon SS, knowing that a lower setting uses less air, yet gives velocity that isn’t that much slower.

A third thing is that the velocity performance of the 1:22″ barrel is so good at power setting 6 that it makes power setting 10 useless. Take that thought just a little farther, and you’ll see that all power settings above setting 10 are pretty much a waste of air in a Talon SS with a 12-inch barrel, regardless of which pellet you use.

If the 1:22″ twist barrel turns out to be accurate, we’ll want to use it in the Talon SS instead of the factory 1:16″ barrel because we’re getting the same performance at power setting 6 that the factory barrel gets at setting 10. On the other hand, there’s not much real velocity difference between the 1:12″ barrel and the factory 1:16″ barrel. So, whichever one is more accurate is the one to go with if the 1:22″ barrel proves not to be as accurate.

That’s all I have to say, but I’m sure that some of our readers will have even more observations to add. Let the discussions begin.

30 thoughts on “How does rifling twist rate affect velocity and/or accuracy? Part 8

  1. Wow! What a surprise. We have a function that lets us schedule when a blog will be posted. I saw J-F’s comment first thing this morning on the last blog posting that there was no Monday blog. There was nothing wrong on our end…but I did see a message next to the time/date it was supposed to go live that said “Missed schedule. 8 hours.”

    If it doesn’t post the blog on time, apparently it won’t post it at all until there’s human intervention. And, even worse, there’s no way to figure out how to make it post at that point. I just clicked a bunch of unrelated buttons, and VOILA! Sorry for the delay.

    I’ll have Pyramyd Air’s IT department check into this. I rate this 10 out of 10 on the weird-o-meter scale.

    Edith


  2. Computers…don’t you luv ‘em?? The only way I was able to find this edition was to click on yesterday’s blog and in the upper right corner was the link to today’s blog. Can’t get here from the Pyramyd home page.


  3. BB just wondering accuracy wise do you think the results might be messed up because the barrels are two different brands with one lothar walther and the others being by quakenbush? Lothar walther is a really good brand and I could see that screwing up results.


    • Cole,

      We will always have that question and be unable to address it. But Lothar Walther barrels are not the finest barrels in the world. Dennis Quackenbush has made plenty of barrels that shoot just as accurately as Lothar Walther barrels.

      What I am saying is we can never get around this, because Lothar Walther is not going to make special barrels for me.

      But here is how you get around it. If Dennis’ barrels shoot as well as the factory barrel in some situations, then we can assume they are equivalent to the factory barrel. It’s the best we can do.

      B.B.


      • And doesn’t the Crosman choked barrel for the Marauder shoot about as well as a Lothar Walther?

        I’m still fantasizing about getting Yugoslav Mauser d98 at a fairly cheap price and swapping it out for a Lothar Walther barrel in 8X57, then getting a trigger job and a good scope…

        How about this story about a Lothar Walther barrel. A man says that he asked a gunsmith to parkerize his gun while plugging the chamber to prevent damage to his Lothar Walther barrel. Perhaps he had planned a project like mine. Trouble is his gun would not shoot straight. He sent it to Lothar Walther, and they said that the chamber had not been plugged and the barrel was ruined by the parkerizing process. The guy sent the letter to his gunsmith who denied everything. So, there are worse experiences out there than mine…

        Matt61


  4. The practical minimum barrel length for any .357 revolver is 4″. A 4″ magnum is compact and often chosen by uniformed police officers who must wear their gun and holster rig all day. Loaded with deep penetrating, heavy bullets it is handy to carry for protection in the field from potentially dangerous predators, such as cougar and black bear. (Works on dangerous two-legged predators, too!) I carry my 4″ Python for that purpose when I am not carrying a centerfire rifle. A 4″ barrel is also a good choice for a dedicated home defense revolver, as it points well and is harder for an opponent to grab than a longer barrel. The 4″ barrel is easily carried in a service type belt holster and you should get something akin to the advertised muzzle velocity (MV), as factory ammunition is tested in a 4″ vented barrel.


  5. B.B.

    Thanks for continiung your research. You’re doing a great work for all of us. And of course we are all waiting for distance/accuracy test.

    Things that come to mind – rifling definitely speeds the pellet down, as some power is used to press the pellet through rifling. Some power is spent just to deform the pellet against faster twist grooves – so faster twist must steal some speed on higher power settings (table seems to prove that) and steal even more on lower settings. Fast twist = medium power I guess. I wish I could inspect pellets to see groove marks – their shape could give a good proof for this theory.

    I wonder if it could be possible to check the same pellet on barrels of the same twist and caliber and same power setting, but one made of steel and another made from e.g. from brass, that has lower friction coefficient to lead. It may bring some interesting results. And then compare same twist same metal barrels but one with standard and another with polygonal riflng. Some people say poly barrel gives better energu efficiency due to better seal – but I nearly doubt that.

    duskwight


    • duskwight,

      As usual, you have given me an idea for this report. I will give you credit when I show it.

      Thanks,

      B.B.


  6. B.B.

    thank you for this scientific quest. I wanted to say that incorporating data tables makes it so much easier to follow these reports. In some cases, data plots are also called for and I am willing to help with such if you ever need it.

    T.E.


    • TE,

      This is a multivariate analysis. If you can find a way to graph it that doesn’t confuse more than it clarifies, I would be open to seeing it.

      Thanks,

      B.B.


      • B.B. and Fred,

        I think that the tables are perfect for this application. However, you will likely want to plot data for other things.

        Now, if you wanted to plot these data, I would use Velocity in the vertical axis against Power setting in the horizontal. Use a different line type joining data points for each barrel. You can use data points sized according to measured group sizes. There, all the data in one plot and not too confusing (I think)

        TE


      • Information visualization! Graphics CAN make the data easier to understand. This is a field of study of mine. As one example, consider the energy maneuverability diagrams of air combat invented by Col. John Boyd which reduce all the variables to a small number with a few colors. What a challenge, but to attempt this, I guess I would have to understand what is going on first…

        Matt61


      • Heh… I just transcribed your table into Excel — but I’m waiting for the rest before loading into the R statistics software… It does have functions for doing things like comparing two groups of data…

        Basically, for your data, the only “numeric” data is really the velocity (and most likely group size later). Power level, pellet, and barrel twist are all “category” identifiers, not continuous numbers. So in the end, R should be able to do evaluations on almost any category breakdown {pellet A vs pellet B; Barrel A vs B vs C; power level low, medium, high}. Granted, I don’t have the statistics background to be sure of formulating valid tests (and the data set is still on the short side — having the per-shot velocities would have given more data: mean and standard deviation).


    • Hey, I tried, too, TE. If you can come up with something clearer than the bar charts that I sent to BB, give it a shot.

      Fred DPRoNJ


  7. Hm, my observation is that if it was a simple as increasing velocity all of our problems would have been solved a long time ago. We would be in the land of … the bogus sniper with his 1600 fps Raptor pellets. And yet–as one finds in the educational field–there are endless ranks of the ignorant to be informed. I was talking to a guy who was telling me about a pump airgun his Dad owned which had to be pumped 40 times.

    Michael, thanks for your encouragement about the Leapers flashlight. But the plot thickens. I asked another friend for whom I ordered the exact same flashlight from PA and she says that all the features are there!? So it appears that the problem is not the Leapers manufacture but the distribution by PA. They sent me the wrong flashlight. Why would Leapers replace the flashlight in that case? Trouble is, PA no longer stocks this particular model, so they can’t replace it. Or maybe Leapers put the wrong flashlight in packaging that indicated something different. And on top of this, the flashlight and packaging are all on the other side of the continent where they were sent months ago. I’m probably going to call it quits on this. At least it’s a good flashlight.

    I’ve been wondering what was the best submachine gun of WWII. (I believe the best submachine gun now is considered to be the HK MP5 unless it has been displaced by mini assault rifles, but I don’t think so.) Anyway, candidates for WWII are the British Sten, the German MP 40, the Russian PPSH series, and the American Tommy gun. The Sten was extremely cheap as was the American Grease Gun. The MP40 had German engineering but the word is that it would jam if it was held by the magazine as it was designed to be. The PPSH was cheap to make but highly reliable with an extraordinary rate of fire. The sight of many German soldiers carrying them on the Eastern Front says a lot. But what of the Tommy gun? I think that the performance was comparable to other guns, but it was heavy, expensive, and complicated to make which are all good reasons to prefer the PPSH. But what of the .45 caliber of the Tommy gun compared to the 9mm of its competitors? The interesting question underlying is how the submachine gun format affect the question of caliber. More to the point, does the stream of bullets increase or decrease the value of the heavier bullet? On the one hand, with a rate of fire at about 800 rounds per minute, you might see the .45 bullet increasing its effect. Or equivalently, you could see the gap between it and the 9mm narrowing as the rounds pour out. Relevant here is the effect of machine guns. I’ve read that wounds from automatic weapons are multiplied by the shock of getting hit several times which overwhelms the body’s capacity to respond so that the wounds collectively are more than the sum of their parts. This would tip the balance in favor of the lighter caliber and the PPSH. And the fact that you can carry more of the lighter rounds (a relevant point today) is further confirmation. But there is one exception. Australian soldiers fighting in New Guinea were loud in their praise of the Tommy gun. They said that there was nothing better for ripping away or through heavy cover. So, if you are fighting fanatical soldiers deep in the jungle, this may be the way to go. But I think any of the models would do for combating elephant poachers.

    Matt61


    • Matt,

      My dad was in the Philippines in WW2. As a 1st sergeant, he got his choice of weapons. He chose the Thompson for the very reasons you stated, even though it was heavy.

      /Dave


  8. Tom:

    Love this series! I’m curious to see how far you can take it. Will you search for the best barrel and velocity for the Premiers and then for the JSB’s (I’d guess at some set range)? So in the end you might be able to say that the CP shoots best in a 12″ barrel (on a/your PCP) with twist X and velocity Y and distance Z (at least with that particular barrel, right?). It would be neat to see – but sounds like a huge amount of testing. The discussions (above) about how to represent the data, graphically, gets more important the more the data explodes in size.

    I don’t think I’m the only one that wants to see you knock airgun barrel twist tradition on it’s butt. Thanks for the hard work!

    Chris B.


  9. I’m more concerned that the two pellets chosen are rather close together in weight…

    Or was that considered earlier in the test — one would think pellet mass might have some sensitivity to twist rate.

    {Forgive any erratic posts — Saturday was cut-over day for the new computer: I finally got enough software and hardware moved from the old computer to the new one to actually swap out the contents of the desk… but some thinks are still TO-BE-DISCOVERED…

    And if folks though M$ Office 2007/2010 with its “ribbon” was ugly… You do not want to see Office 2013. After years of colorful title bars, then the WinXP rounded window corners… Office 2013 looks like the GUI was cut out of construction paper — no shadowing/texture, absolutely square corners… My 1985 Amiga had more attractive GUI. I’m guessing it’s M$ attempt to go to online subscription with Office 365 and not being able to send all the fancy graphics over the net, so they went pure rectangles for 365 and 2013}


  10. G’day BB,
    Looks like the FX barrels are on the right track. Minimal rifling and a long “friction less” push tube.
    Cheers Bob


    • Bob,m

      I know very little about the FX Smooth Twist barrel, except Fredrik Axelsson says it isn’t the most accurate barrel, but it is very good. I also hear that they have narrow velocity bands in which they work well.

      But I have never tested one.

      B.B.


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