Some thoughts on airgun projectile stability

by Tom Gaylord
Writing as B.B. Pelletier

A history of airguns

This report covers:

  • Pioneer airbow
  • Rifling
  • Hop-Up
  • Projectile finish
  • Summary

I’m writing this from my hospital bed on Saturday, though I hope to be discharged later today. I would like to thank Val Gamerman for covering the blog for me last week. I was unable to do much of anything, and my thanks to all of you for keeping things going. This will be short, because of my situation. Let’s talk about airgun projectile stability today.

Pioneer airbow

When I shot the Benjamin Pioneer airbow at the SHOT Show this year I was amazed by the accuracy it gave. Not just when I shot it, but also there were two cases where one arrow went inside another one at 30 yards. Television’s Mythbusters proved that a regular longbow cannot do that because the arrow is constantly flexing as it flies, but the Pioneer pushes the arrow from the tip (it’s hollow inside) rather than from the back end and it doesn’t flex in flight. That got me thinking about what has been done about airgun projectile stability and what remains to be done.

Rifling

Most people know that rifling spins the pellet and stabilizes it while it flies. But there is a lot that hasn’t been done in this arena. Most airguns are rifled with a 1:16″ twist rate that seems to work pretty well. There have been some barrels with a different twist rate, but more research needs to be done. I did a huge test on barrels with 3 different twist rates that you may want to review. I was not able to match the pellet to the twist rate in my test, but that’s a place when more could be done.

The Smooth Twist barrel from FX and also from the earlier Swedish Excellent is another place to be considered. Has the optimum combination of rifling length, twist rate and rifling depth been found? And has it been paired with an optimum projectile yet?

Another place to consider is the gain twist rifling. I don’t believe anything has been done with that in an airgun. Would a gain twist that starts at no twist and increazses to 1:16: be better that a straight barrel? Would it act more like a Smooth Twist barrel?

Hop Up

We saw a pretty dramatic example of what Hop-Up can do for an airsoft BB last week. Hop-Up puts a backspin on the ball before it leaves the barrel. Would it even be possible to put a Hop-Up on a gun that shoots steel BBs? A number of readers have asked this and a couple are experimenting with it.

Projectile finish

One area that has been left alone is the surface finish of a pellet or BB. We know that golf balls fly better because of the dimples on their surface. Would that also held BBs in flight? Would the BBs have to be spinning for it to help? What would the indents (or protrusions) have to look like? How deep/high would they need to be?

Would changing the surface finish of a diabolo pellet have any affect on stability? Where would the finish go?

Summary

These are a few of my thoughts on the stability of projectiles in flight. Other thoughts might include darts, conicals bullets in big bore airguns and more. What have I forgotten?

87 thoughts on “Some thoughts on airgun projectile stability

  1. I am glad you are recovering, I hate kidney stones, and I feel your pain.
    My wife had the laser blasting surgery 2 weeks ago, and is still passing “sand”.

    I wish you a speedy recovery.

    On the myth buster special (I missed that one). By long bow, do you mean an actual long bow, or do you lump compound bows into that group as a general term for something other than a crossbow or air bow?


  2. Hi BB,
    I have a question regarding a 10 meter match pistol. I have a good friend and shooting buddy who has inherited a Walther CP3 match pistol. It has three different co2 tanks and is fitted with an angled tank adapter. My friend is interested in selling it, and I may make him an offer. It is heavily used and the grips are majorly modified for the female shooter that previously owned it (I’m assuming that her hands were much smaller than my very large hands). I am curious as to whether I should shell out some cash for this pistol or save for something newer (and pcp). I don’t think my scores will improve much as I just started practicing 10 meter air pistol in January and I have only this last couple of weeks began to shoot over 500. I have been shooting a Gamo Compact with some work done to the grips and added some lead to the underside of the muzzle. Should I be interested in this gun, and if so, what is a fair price to offer?

    Thanks for any help you can provide. I know you are the guy to ask for all things involving 10 meter air pistol.

    -DMoneyTT



    • DMoneyTT,

      Wow, that is a tough question. You will probably need to get new grips if you have large hands. Expect to pay around $300 for a set of those.

      I might offer $300 for the gun, expecting to put another $300-400 into it to get it operational for me.

      Three tanks sounds like a good thing, but you’ll never use them all. It’s like buying a car with 3 5-gallon gas cans. Sounds nice but most people don’t operate that way.

      I’d keep looking.

      B.B.



  3. Boy oh boy BB, your body may be at rest but that mind is working overtime !
    Don’t know if many people know what an FX smooth twist barrel really is … I thought they had a gain twist with the smooth bore? Hope a lot of manufacturers read your blog.

    Bob M


    • A follow up. “The smooth twist portion” of the (FX) barrel ….. Referring to barrel blanks for sale, AOA. Perhaps it is not a gaining twist but only a portion of the barrel is twisted giving the pellet time to gain velocity before being twisted.



        • Bob M
          Had two FX Monsoons. The smooth twist barrels are very accurate. And yep just the end of the barrel is rifled.

          The idea is the smooth bore part of the barrel offers less drag and allows the pellet to accelerate faster before it hits the rifling at the end of the barrel.

          And I wonder if the speed of the pellet in the smooth bore part of the barrel allows the pellet to engage the rifling better. And that’s possibly why the smooth twist barrels are accurate.


          • Totally agree, and short AOA film confirms it. I live on three and a half acres and my FX Independence is a one shot one kill rifle…..If I use it right ! Tend to get complacent and take it for granted.


            • Bob M
              Have you seen the video of the FX factory tour.

              One part of the video shows them putting the muzzle end of a barrel in a machine. It makes me think the twist is just that when it’s done. Can’t confirm but it seems the barrel is held by the machine and the tip of the barrel is twisted.

              Then another part of the factory tour video they show the barrel being straightened and trued by spinning it on v blocks if I remember right with a indicator.

              Pretty cool video I think anyway.


              • GF1,

                The smooth twist design has been around for some time. They used to use that type barrel on Mattelomatics. They were horribly inaccurate.

                The barrel end is not twisted, it is compressed around a mandrel that has the rifling reverse engraved in it. As you can well imagine, it is much faster and cheaper than rifling the entire barrel.

                It is my understanding that the older FX rifles were not that accurate. They even went to Lothar Walther barrels for a time until they got the smooth twist right.


                • RR
                  Interesting info.

                  You mention the mattelomatics. Then went into explaining how the barrel was made.

                  Was that explanation how FX does the barrels now or how the mattelomatics were done?



        • From Wikipedia:
          In the 1960s smoothbore tank guns were developed by the Soviet Union and later by the experimental US–FRG MBT-70 project. Based on their experience with the gun/missile system of the BMP-1, the Soviets produced the T-64B main battle tank, with an auto-loaded 2A46 125 mm smoothbore high-velocity tank gun, capable of firing APFSDS ammunition as well as ATGMs. Similar guns continue to be used in the latest Russian T-90, Ukrainian T-84, and Serbian M-84AS MBTs. The German company Rheinmetall developed a more conventional 120 mm smoothbore tank gun which does not fire missiles, adopted for the Leopard 2, and later the U.S. M1 Abrams. The chief advantages of smoothbore designs are their greater suitability for fin stabilised ammunition and their greatly reduced barrel wear compared with rifled designs. Much of the difference in operation between smoothbore and rifled guns shows in the type of secondary ammunition that they fire, with a smoothbore gun being ideal for firing HEAT rounds (although specially designed HEAT rounds can be fired from rifled guns) and rifling being necessary to fire HESH rounds.

          Most modern main battle tanks now mount a smoothbore gun. A notable exception are the tanks of the British Army which used the 120mm Royal Ordnance L11A5 rifled gun until the 1990s; it was then replaced it with the 120mm L30 rifled gun which remains in service. The Indian Arjun tank uses an Indian-developed 120mm rifled gun.


  4. On the splitting arrow thing…contrary to myth-busters, splitting a previous arrow is extremely possible and decidedly not something to be done on purpose. I destroyed three in one day, and that’s far from a boast. Oh, yes, them arrows ain’t cheap, each one costing at least as much as a 500 tin of excellent quality pellets. You think air-gunners are an anal-retentive lot? Ha! Pick up a bow and head for the range. You’ll find grey-heads debating whether green paint on the tips is more accurate than red. Really.
    (Red shafts are easier to find in the weeds, however.)
    Believe me, I’ve nothing against myth-busters, and completely enjoy and admire the show. I even shoot at the same range they do. But I have to say, their methodology is not always the best…particularly as I happen to live down-range from that pesky cannon-ball incident from myth-busters of a few years ago. Look it up.
    But, hey, we’ve all learned to disregard the, “Relax, we’re experts/professionals/certified/etc, disclaimer, right?


  5. BB
    Glad you wrote this. And glad your ok.

    First the arrow shooting air gun and how the air makes the arrow fly. That reminds me of the new hollow lead free pellets from Sig. I think that is a step forward in pellet design.

    And twist rates and pellets that is something I have always been interested in. I know you have to remember me talking about taking the FX smooth twist barrel to the next level by making screw on tips with different twist rates that can be tryed with different pellets. Kind of like different chokes on a shot gun.

    Then comes the Air Venturi wing shot air shot gun. I asked if there was going to be a tighter screw on choke available for it. I see that there is one available now for it. And remember its a smooth bore that shoots a bullet also. Well there you go. Let’s get some screw on tips with different twist rates available for it next. Talk about a hunting tool. The wing shot would be able to do multiple roles very effectively by just screwing on a new tip. Cool stuff there.

    And now that you talk about finnish on the pellet. Hmm got to think about that one. A pellet with a ruff outside finnish might be good for stability in at closer ranges. But out far I think it would slow the spin rate of the pellet down and how fast the pellet was moving. Now on a round ball that may produce better results.

    And then about a ruff surface on a pellet and engaging the rifleing. Maybe that ruff surface would foul the rifleing in the barrel. Maybe it would shear off some of the lead as it made its way down the barrel. Just don’t know about that idea.

    Oh and the hop up. Maybe even a round lead ball would work good out of smooth bore gun like a 760. Then comes the thought of having a ruff dimpled surface on the lead ball like a golf ball. And shoot it out of the smooth bore 760 with the hop up mod that we are talking about. That just might be a good combination there. That might make the round lead ball more efficient in flight. Might only need 5 pumps from the 760 to go the same distance as 10 pumps. And possibly keep the round ball more accurate at longer distances.

    I just wonder if behind the scenes that the pellet makers are experimenting. Heck look at the pellets JSB has been releasing. They just released a 33 grn .22 caliber diablo pellet. And no mis-type there. Really a .22 pellet that heavy.

    I think there is more experimenting needed to be done with pellets and twist rates and such. I’m thinking that air guns will get more accurate in time. Got to have a accurate gun before you worry about the type of sight you use ya know.


  6. B.B.,

    Good article. Some things are easier for the home modder to do, and others are not. I have done darts and still working with them. Amazing power out of an 880 with only 5 pumps and a 30-35 grain dart. Then the arrows. That was fun and I learned a lot. My experiment was spot on in many regards and it did work,….. just not enough power. Once I get the M-rod, if I could ever get a roughly .250″ od barrel, the test would be back on and I believe would be a complete success. Then the steel bb hop up…….. still working on that. The magnet test did show that it impacted POI and I believe that was due to inducing spin,…… but,….. the accuracy was worse. Actual hop up with the bb contacting a rubber “tip” towards the breech end is next on a 760 platform.

    Again, good thought provoking article and,…….. glad you are back home. I am sure the cats are glad. Chris


    • I’ve tried a 1/4 inch ID aluminum tube as a barrel that I got from a hobby shop on a Crosman 66 conversion. I started with larger ID tubing and just keep sleeving smaller tubes into it. 13 inches seems to be an optimum length for the air capacity of the valve. Three strong disc magnets at the end of the steel shroud for the barrel seem to give the best accuracy. It seems to hit pretty hard at 20 yards but not consistently enough for hunting.


      • Brent,

        So,… the whole idea was to shoot sling shot ammo? I think the thicker the barrel, the less impact magnets will have. I think that it takes something with the power of an M-rod to do arrows and heavy projectiles any justice. Or some other = PCP platform.


        • Chris,

          I’ve always been kind of infatuated with Lewis and Clark’s airgun. The idea was to see if I could make a poor man’s Big Bore out of a multi pump. I tried a 40 caliber aluminum barrel, a 375 caliber steel barrel, a 348 caliber copper barrel and now a quarter inch aluminum barrel. All pretty much had rainbow trajectories beyond 15 yards except for the quarter inch barrel. There’s just not enough volume in the Powermaster 66 valve to get them going above 250 fps. The 25 caliber appears to be an exception. It will be interesting to see what it chronies at.


          • Brent,

            Best of luck with you adventures. I still think a PCP is the best platform. I have nothing to base that on though other than arrow testing and some 30-35 grain darts in a multi pump. The darts are serious, the arrow not so much.

            I like the way you think though!!!!!! 🙂 Keep up the testing and keep us all informed.



  7. Everyone,

    Yes I am back, but I’m not to 100 percent yet. I’m still passing stones and there is some back pain that I can work through. I am tired and those who are worried about me pushing too hard can relax. I plan to take it slow for awhile.

    Good to be with my kitties again though. 😉

    B.B.



    • B.B.,

      Cats can be funny after a time on their own. A friendly one will be standoffish for a few days, and others won’t leave you alone and are under foot,…. more than normal. I imagine that you can relate.



  8. B.B.
    Continued success on your way to recovery!

    In your previous article on rifling and twist rates, I was amazed at how fast the pellets spin. Do big artillery shells spin super fast?
    Does an FX barrel impart a slower spin rate? Less groves to get the pellets turning…
    The idea of a screw on barrel end that imparts a spin is very interesting. Do you know if anybody has tried anything similar before? Great idea, just can not imagine that it has not been tried before.
    Feel better and take it easy,

    -Yogi





      • I’ve only passed one stone that I recall but a piece of slavery down the collar during winter really lit me up.
        My shirt was tucked in so it stopped at my belt line momentarily until I tugged on the waistband and it then stopped at the bottom of my underwear sealing my urethra, until I had to relieve myself which hurt but.my next trip to the restroom wasn’t pretty or silent.


      • BB
        That is the truth. Long story short and over 4 months of time. Before I went into the hospital to have my operation from the diverticulitis. It was the worse pain I ever felt. Couldn’t see straight. It’s like I would black out. Only thing I knew was pain.

        Then the stent after the first operation wasn’t no fun either as well as all them staples they had to remove at the doctor’s office.

        Like I said before. I try to do what I can to stay out of the hospital. Not no fun being sick.

        BB hope you get through with this fast. And back to enjoying things.


      • B.B.,

        I have been lucky compared to most folks. With me it wasn’t just the size. They were shaped like the business end of a mace or flail or whatever that Medieval weapon was. Or a spiny sea urchin.

        Michael


  9. I tried a quarter inch ID aluminum tube on a Crosman 66 power plant with three strong disc magnets at the end of the shroud. Shooting quarter inch slingshot ammunition, I would get some decent groups and then a bunch of random fliers at 20 yards. It appeared to hit hard but not accurately enough for any kind of hunting. I’ll have to continue experimenting with different configurations of magnets


  10. There’s also the problem of the flat spots on the sides of the slingshot ammunition to contend with, especially getting them aligned consistently so that they don’t affect the flight of the ball.


  11. B.B.,

    Sorry your weekend didn’t go to plan. Hope you’re feeling better and better. Great to see that you’re feeling well enough and/or bored enough to blog from your hospital bed.

    I agree that the airgun twist rate is a very interesting question, even if the answer in the end is that good old 1:16 remains the de facto choice. It’s “fun” in the firearms world that we have a massive enough selection of bullet lengths and velocities to make the twist rate so critical. Airgunners are a fiddley, tinkerey bunch. We probably need a bigger twist-rate ecosystem like we need holes in our heads, but maybe we “need” it just the same!

    Take care of yourself.

    -Jan


  12. Welcome back, B.B. But don’t get carried away. I’m getting surgery on Wednesday for my foot and don’t expect to be very productive.

    If you’re talking about one arrow splitting another, I don’t see why that would be impossible with a regular bow. A flexing arrow would make it more difficult, but i don’t see why it couldn’t split another arrow if it hit just right.

    Matt61



      • Splitting the arrow would likely have little if anything to do with compound vs long bow or recurve. The basic difference is how the power curve on the release is accomplished. A compound bow uses a system of eccentric cams to “stack” the power input towards the the beginning of the draw. Once “over the hump” it becomes much easier to hold the bow/arrow rig for carefull aiming, rather than trembling mightily while attempting to hold 50, or 75, or however many pounds of stored energy.
        The waving arrow is clearly visible to the archer as it goes down range but whether it splits, shatters, or grazes has far more to do with the construction and relative sizes of the arrows. A wooden solid shaft like Locksley used would most likely shatter. A modern aluminum arrow is a hollow tube and would more likely split. An even more up to date carbon fiber arrow, likely a smaller diameter than an aluminum arrow, could possibly travel the full length of the larger diameter aluminum tube wth little apparent damage (but both would be ruined, in fact.)
        Most likely of all, stacking one carbon fiber arrow atop another would generate something apparently involving one of those Rambo exploding items, What a mess and have to be extracted from the target like grabbing a handful on splinters and pulling…which is exactly what you are doing. Carefully!
        Somewhere I have a Xerox of a pair of fatally involved carbon fiber arrows I made for my Dad when he said he didn’t believe it possible. But he also became a believer.


  13. I just had another surgery not long ago myself: the big toe on my left foot was purple and not getting any better after that nasty spill I had when my chain derailed last summer.
    Turns out I had a significant cholesterol blockage impeding circulation.
    They wouldn’t let me leave the hospital even to lock my apartment.
    They couldn’t get a pulse until they got up to my groin and dispatched an ambulance to transport me to Abilene.
    It took 2 weeks in the hospital to perform a simple angioplasty! The whole time I was hospitalized was very stressful because I had stuff I needed to get done at home. Sure enough the power was cut off when I got home.



  14. Ran across a cool gun today at the pawn shop while shocking my 760 & RedRyder, it’s definitely overpriced but I have been able to make a couple good deals with them before.
    It’s another tube fed semi- auto that shoots shorts, longs & long rifle .22 rimfire: Savage 187n.
    Anybody know this gun?
    I’d sure love to have my Rem. 550i going again but to purchase the parts necessary to make it functional new would put me in it for double it’s value so I’m hoping to get a deal on a donor for it which has already been 2 years in the process.
    If this gun is anything like my 550 I’d like to have another.
    Thanks!

    Reb



  15. Seems to me airgun development and advances are outpacing projectile development. How about a sabot ‘bullet’ aerodynamically designed for high speed long distance shooting for example. Perhaps we could ‘unleash’ the power available with magnum springer’s and PCP’s. I could see projectiles designed for just about every use and power range. I think we are heading there and thinking out of the box, but for now replacing lead, and gaining speed, seems to be a top priority.


  16. B.B.,

    It occurs to me that I am interested in barrel length as well as the rifling possibilities. Of course I am only concerned with PCP’s, pneumatics, and co2 variants (without concern for any restraints imposed by the shooting environment).

    ~ken


  17. I feel compelled to resurrect an old conversation from a couple years back or so.
    It started with the H&N rabbit magnum pellets no-one seems to be able to wring any accuracy out of.
    My initialsuggestion to them was to swage a deep hollow recess in the base of their existing stock, then the idea evolved in my thoughts into a much longer projectile with a recess that extends all the way to the back of the pellets head, making it more of a shell.
    Such a projectile would be very fragile and then packaging came into play.
    I think JSB has the closest thing I’ve seen to this design so they have a jump on the competition and I’d like to have some input.


    • Reb,

      I like it. Like the airbow,…. the pellet is driven from behind the head and not from the tail. Drill some and find out! 😉 Epoxy 2 pellets together and drill to the back of the head on the lead pellet! 2 heads,…..1 skirt! Notes made,….. I will try it with some lighter .22 pellets and send ’em down the springers! How’s that for some “twisted” testing????? 🙂


      • I’m thinking these may be excellent lead-free pellets,they could be comprised mostly of Zinc with a thin coating of softer metal or even non residual plastic.
        I also believe the airbow was a direct result of experimental exercises discussed in the comments section of this blog and I welcome their willingness to pursue these “outside the box” projects.


      • Chris,
        What would you gain other than a heaver pellet ? They need a better aerodynamically designed pellet. I see your point though, it ‘is’ a new design. What the heck ?


        • Bob,

          Well,…. nothing other than that the force applied to the pellet would be applied to the head of the pellet rather than the tail. The 2 pellets epoxied together would only lengthen the inner “chamber”. Plus, drilling out the core would lighten the pellet. I will try. Watch and see, someone will come out with that pellet. Gimmick? Maybe. But I will be at the forefront on trying it.


    • Reb,

      The HN Snipers are close to the 10.34 .177 JSB in shape. I did see some pellets that expanded at the waist. I do believe that was due to more compression, rather than inner expansion though.



        • Reb,

          They come in 14.0 and 18.0 in .22. The 18 punched both sides of a steel soup can at 70 yds..

          Amazed the heck out of me. Hold over was getting a bit extreme at that range though. The 15.89 JSB will do it too, but it takes a square hit. The 18 was on the right third, but it did it.


          • Chris,

            You’re talking about the H & N Snipers, right? What were you shooting them out of — your TX? How accurate would you say they are?

            A friend had just emailed me a link about them a couple of weeks ago. I was skeptical they would do well out of a springer, thinking they were designed more for PCPs.

            Jim M.


            • JimM,

              I got them over the winter and have not put them to any extensive group testing. The one I did with the 18’s I got 3 1/4″ on paper at 50 yds. with the .22 TX with an HO kit from Vortek and shooting 628 fps. with JSB 15.89’s. I tried them because GF1 likes the 10.34’s by JSB in .177. They have the same profile. Long straight waist and short skirt. I have the 14’s and the 18’s in the Snipers. I got 1″ at 25 yds. with the 14’s. That was both 10 shot groups.

              I am not the best shot, so keep checking back for further progress on the Snipers. I will say, all HN’s fit tight in the LGU and TX. JSB’s and AA’s fit “just right.


  18. Found a very interesting highly technical blog entry on the Yellow challenging the max velocity of air molecule movement 1640 FPS. A claim that over 2000 FPS is possible due to many variables encountered in discharging a PCP airgun, such as the increase in temp from air being compressed again behind the pellet. I know burning oil just about turns it into a firearm. Harnessing those variables could take airguns to a new level of power.


    • Bob,

      On the second tune on the TX which I thought was all “clean and proper”,…. the first shot was like a .22. The combustible substance would need to be added in the comp. chamber for max. effect. Recommended?,…Not!
      I do like your train of thought though.


    • Bob M
      The H & N Barracudas were developed for a air gun that used a injection of either I believe. Can’t remember exactly right now. But the head of the pellet was getting blown out.

      I believe that the gun existed in the early 70’s when the horsepower air gun velocity wars was taking place at that time. And they were trying to achieve a high velocity with lead. Not going light weight with alloys and such.

      And was that Lloyd’s experiment on the yellow?


  19. Oh how about the dumbell shaped projectiles. Is that one you forgot BB?

    Wasn’t there a person that used that design in a smooth bore airgun and got very good results.


  20. BB, hope you get to feeling better quickly!

    I’ve been reading a 2013 blog about lubricating pellets. There is Part 1 and Part 2, but I can’t find any more. Am I not using the search function correctly or has another installment not yet been written?

    Motorman
    St. Louis, MO


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