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Big Game Hunting Big bore bullets: Part 2

Big bore bullets: Part 2

by Tom Gaylord, The Godfather of Airguns™
Writing as B.B. Pelletier

Part 1

This report covers:

• The dumbbell bullet
• Did those bullets make a difference?
• Longer bullets must spin faster!
• Shorter bullets need less spin to stabilize
• Less contact with rifling reduces friction
• Summary
• Pyramyd AIR Cup

Let’s look at big bore bullet design. I’ve written about this before, specifically in this report back in May 2007. And I told you about a big bore contest in which a smoothbore shooting special bullets out-shot many rifles. Let’s look at that first.

The dumbbell bullet
At the 1999 Damascus, Maryland, airgun show, we had a big bore shoot in which about 25 shooters competed. Among them was a father-son team of Bob and Mike Chilko, who each had a big bore gun they had made themselves. Bob shot a .398 underlever, and Mike had a front-pumper that had to be pumped 30 times for each shot. Both guns were smoothbores that shot strange-looking dumbbell-shaped slugs. The funny thing was that they outshot most of the other competitors for accuracy, which included hitting a 4-inch target at 40 yards. In 1999, that was a quite a feat for a big bore airgun — especially a smoothbore!

dumbell bullet
The Chilcos shot bullets that looked like this. The shape promotes high drag that stabilizes it in flight.

When I saw those bullets, I knew what they were and why they worked. They were an adaptation of the French Balle Blondeau shotgun slug of the 1960s that revolutionized all shotgun slug shooting. Before the Balle Blondeau, shotgun slugs were doing well to group within a couple feet at 100 yards. They were considered 40-yard projectiles at best. But the Balle Blondeau allowed run-of-the-mill shotguns to put five shots in 6 inches at the same 100 yards. It was as if rifling had just been invented!

Balle Blondeau
The French Balle Blondeau shotgun slug stabilizes in flight by using drag — the same as a smoothbore pellet gun.

I asked the Chilkos if they knew about the Balle Blondeau and they said no. But Mike was an engineer who figured out the same basic aerodynamics independently, and then demonstrated them to all who attended that match!

Bob Chilco
Bob Chilco pumps his .398-caliber homemade underlever big bore airgun.

Did those bullets make a difference?
Within one month of that match, Gary Barnes was casting lead dumbbell-shaped bullets for his own big bore rifles. He called them spools, which is a very descriptive term. Until those bullets came along, shooters were happy to put five shots in 4 inches at 50 yards from a rifle. Several months after he started making his spools, Barnes was grouping better than that at 100 and eventually at 200 yards! So — yes — those bullets made a huge difference!

I’m not advocating this bullet shape as the only kind for big bore airguns. I’m not even saying they’re the best. With today’s rifles able to shoot faster and faster, we can stabilize conical bullets quite well. When it comes to penetration on game, a conical will out-perform these dumbbell-shaped bullets every time. But we learned a valuable lesson in aerodynamics from this bullet shape, and we would be foolish to ignore it.

Longer bullets must spin faster!
If shooters have learned anything in the past 50 years it’s the lesson that longer bullets have to spin faster to stabilize in flight — all things being equal. The American Army learned that lesson in Viet Nam, when our M16 rifles started out with a 1:12-inch twist (one rotation of the bullet for every 12 inches of bore travel). Their bullets were barely stable under ideal conditions, and they quickly lost stability in flight. While they did well at short ranges under 100 yards, you could not hit a man-sized target out at 250 yards and beyond, which put the American troops at a tremendous disadvantage.

The M16 twist-rate debacle came about from a too-short development cycle and a design that was rushed to production for political reasons. Had the developers been shooters with a knowledge of firearms history, they would have known that this path has been traveled before in the 1920s. But if anyone on the development team knew that, no one listened to them and the lesson had to be relearned at great expense.

There are 2 ways to spin a bullet faster. Either speed up the twist rate or increase the velocity. The length of the barrel has nothing to do with how fast the bullet spins, despite what you may have heard or read. A bullet that leaves the muzzle of a 1:12 twist rate barrel at 1,000 f.p.s. is spinning 1,000 times per second (1 turn every 12 inches), and the bullet is moving 1,000 feet (1,000 X 12 inches) per second. Increase the velocity to 2,000 f.p.s., and you increase the bullet spin rate to 2,000X per second. Or you can leave the velocity at 1,000 f.p.s. and change the twist rate to 1:6.

The bullet loses velocity fast as it moves downrange, but the spin doesn’t slow down at the same rate. Even when the bullet is 500 yards away from the muzzle, it’s still spinning fast enough to stabilize (assuming it was stabilized to begin with).

Big bore airguns are generally slow, so their spin rates are also slow. They don’t stabilize long bullets very well. When we test them for accuracy, this is what we discover.

Do you think these 68-grain bullets might be unstable? They have keyholed (gone through the target sideways) because they’re tumbling in flight. Even centerfire rifles that shoot over 3,000 f.p.s. like this .219 Donaldson Wasp need the correct twist rate to stabilize their bullets.

Shorter bullets need less spin to stabilize
If you don’t want to speed up the rifling twist rate, another way to improve accuracy is to shoot shorter bullets. Regardless of the caliber, a shorter bullet needs less spin to stabilize. So, big bore shooters need to avoid those bullets with long noses and concentrate on bullets with shorter noses.

I learned this lesson early on with big bores, but it never ceases to amaze me that other shooters are still discovering it for the first time. It’s reported in the literature time after time, yet some shooters continue to disregard what others have been reporting.

Both bullets are .458 caliber, but the one on the left needs to be spun a lot faster to stabilize it in flight.

Less contact with rifling reduces friction
A bullet doesn’t have to make contact with the bore along its entire body. With the right design, the bullet can have as few as 2 bands that engage the rifling, while the main body is slightly narrower and doesn’t touch anything. The dumbbell bullet at the beginning of this report is one example of that, but the difference in size doesn’t have to be that great. By making the main body of the bullet just a few thousandth of an inch narrower than the top of the rifling, you can get the same result and still have the bullet weight you need.

contact bands
The bands are the only part of the bullet that contact the rifling. This can be reduced to just the top and bottom bands by design.

You can take these lessons and apply them anywhere. For example a bullet that has a deep hollow point or a hollow base will be longer than a bullet of the same weight and caliber without those features. Since length needs a faster spin, shooters want to be careful of those types of bullets. That’s not to say that they can’t be used, but some thought needs to be given to their effect on stability in flight.

That’s a look at some of the most important things we know about big bore bullet design today. They’re simple lessons, but they have a profound impact.

Pyramyd AIR Cup: October 24-26

Pyramyd AIR Cup
Pyramyd AIR has put together a 3-day shooting event called the Pyramyd AIR Cup. There are so many airgun events that they couldn’t stuff them all into one day!

The festivities start on Friday, October 24, with an open practice range and the Payday Challenge. For just $5, you can shoot at targets at varying distances and kill-zones. The best shooter will take home $200. Not a bad return for a $5 investment!

On Saturday, October 25, head toward the sight-in range to make your last adjustments before you start the Silhouette Offhand Competition. Read more on this page (scroll down to find the Offhand section). In the afternoon, there’s a field target competition.

The last day of festivities is Sunday, October 26, and a field target match starts it off with a bang. That afternoon, the second silhouette match will be held, and it’s the Gunslinger Competition. Read more about it here.

AAFTA (American Airgun Field Target Association) rules will be followed for both field target matches.

After the competitions are over, there will be an awards ceremony and the big $1,000 Grand Prize will be awarded. Yes, you heard that right: 1,000 big ones!

Register online for the competitions, lunches and a dinner banquet held on the last day. You can attend all events or just a a few. The more you enter, the greater your chance of being the Grand Champion of the day. Even if you don’t win the Grand Prize, you can still win some super runner-up prizes.

There will be door prizes for anyone not participating in a shoot. Some of the items that will be given away are an AirForce Talon SS PCP rifle, a Hatsan Galatian QE PCP rifle, a Walther LGV spring-piston rifle and a Hawke Sport Optics Sidewinder 30 8-32×56 scope.

I’ll be there, too, as will airgun hunter Jim Chapman and Airgun Reporter Paul Capello. Come to shoot. Come to try out guns you’ve always wanted to shoot. Come to chat with Paul, Jim and me. Come to immerse yourself in the world of airguns.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

95 thoughts on “Big bore bullets: Part 2”

  1. BB
    I think you meant to say keep the velocity at 1000 fps and change the twist rate to 1:16 not 1:6. Its where you were talking about there is 2 ways to increase the spin rate on a bullet when you was talking about the M16.

    And I enjoyed reading Part 2 of the big bore bullets.

    And them are some nice door prize’s that will be given away at the Pyramyd AIR cup.

    • Gunfun
      No he meant 1 in 6 twist rate that would make the bullet spin at twice the rate at 1000 fps than a 1 in 12 twist would. Remember its one rotation in 12 inches in a 1 in 12 twist and one rotation in 6 inches in a 1 in 6 twist rate. So for the bullet to spin at a faster rate you either need to, increase velocity or increase the speed of rotation. a 1 in 6 twist would rotate the bullet twice in 12 inches of barrel length instead of once in a 1in 12 twist.


        • Gunfun
          I figured you had to many number running around in your head and it just did not click with what BB was saying.
          I am glad to know what the twist of most air gun barrels is also as I thought it would be a little faster to stabilize such a light projectile.


            • Gunfun
              I know the feeling it was the same way when I worked at Harley with part numbers, work order numbers, calibration numbers, COV numbers( company owned vehicles ) mileages and so on.


              • buldawg
                I adding and subtracting numbers and half of diameters and adding thickness and all that good stuff all night. While I’m drilling and milling and tapping.

                But I love it for some reason.

                • Gunfun
                  If Harley was still here in Alabama I would still be there working with my arthritis and all my other conditions because it was like never going to work, but rather just going to my other shop to play with what I loved to do just like you do.

                  I felt like I never worked a day in my life after I got that job.


                  • buldawg
                    I’m a person that likes to change things up. Something new to keep me excited.

                    Its amazing that I stayed doing my job as long as I have.

                    But as it goes there is something new to do every day with my job.

                    • Gunfun
                      I can understand that also. but at Harley they had such good benefits that I would be hard pressed to find a job that paid as good with all the bennies to go with it.

                      I was making 25 bucks an hour with anything over 40 time and half, Sundays double time and holidays double time and half. four weeks vacation a year with Christmas to new years closed with pay so it was another week vacation, 30 bucks a month health coverage for family that had health,. drugs, vision and dental. half a million in life insurance for 175 buck a year, short term disability at full pay for 6 months and then70 % for 18 months and a corporate American express card for any travel expenses to be covered. Short term incentive program ( STIP ) that would pay you a bonus depending on how well the company did profit wise that was anywhere in the 11 years I was there came to a low of 4% to a high of 11% of total yearly earnings including overtime paid in February of every year and at the 11% payout I got a check for 5000 bucks When you figured it up to what they called total compensation I was making 83,000 dollars a year. and that was doing what I loved so it was never really work, I could not just walk away from that. But all things change and now i am where I am and making the best of it.


                  • buldawg
                    The benefits are fair at the place I work. But the pay is real good. I can’t post what I make an hour because some of the people at work read the blog here and there. I don’t want to start world war lll at work tomorrow you know what I mean. We all make good money though I’m sure.

                    The 2 other guy’s that I work with we have worked together for 30 years now. And crazy as it may be we all get along good together and hangout and shoot guns at times. That makes a difference also when you work with people you get along with and have things in common.

                    • Gunfun
                      I does make a difference when you work with people that have the same interest as you and can have friendship outside of the job.

                      Most of the people at Harley were all bikers so we all pretty much shared the same interests and I am still good friend with several of the one I worked with a we get together one a year in November for the TTF social club to catch up on everyone’s lives and just have a good time. then I have a couple that I used to go riding with almost every weekend until My heart caths and arthritis all cropped up at once and make it hard to pull in the clutch on the Harley.


                    • Gunfun
                      Like I said it was the kind of job that you feel like you are not working, but just doing what you love and getting paid to do it.

                      I did not own a Harley before I started working there and probably would not today if I had not got the job there. I was always a Yamaha or Kawi fan in that I owned Yamaha dirt bikes and Kawi street bikes. But never anything new as I preferred to by used cheap bikes and fix them to the way I wanted them to be, the newest bike I have ever owned for the street is my 77 KZ1000 and the newest Yamaha for the dirt is my 74 SC500 MX. then my 76 Harley super glide that is built to outperform any new Harley they make and does so with relative ease especially in the top end department. I have yet to come up on a street legal Harley that I cannot pull away from at 110 mph where they all fall on their face mine is just starting to pull hard.

                      It was much different working for the Motor Company than in a Harley dealership that is for sure.


      • BB
        Yep I was at work reading through real quick and I’m sure I still had numbers flashing in my brain. That’s what I have to do all night is remember numbers or write them down when I’m making things.

        I wasn’t thinking about the 1:6 distance being half of the 1:12 in your explanation I was just looking at the numbers. That’s what happens when the eye’s and brain ain’t connecting.

        And this question was on my mind and forgot to ask about it in the past. I know your talking about big bore air guns.
        But I believe that you said in the past that most smaller bore air guns were 1:16 twist barrels.

        Do they use the slower twist rate; 1 revolution per 16” that the pellet travels because they are relying on the diabolo design to stabilize the pellet?

        And the other part of the question. Is that slower twist rate used to reduce how much pressure is needed to push that pellet out of the barrel? Would it take more pressure to push the same pellet out of a faster twist rate barrel?

        • GF1,

          Airguns use a 1:16 twist rate out of convention. And they are al;sp drag stabilized, so the spin doesn’t have to do as much.

          I have tested the velocity of fast-twist barrels to slow-twist barrels in the same guns and the difference isn’t that great. Read this:



          • BB
            Yep I remember that. I made some replies also on that one.

            I guess the question would be if I rephrase it would be. Would you get more usable shots per fill out of a pcp gun with a slower twist barrel verses a faster twist barrel?

            If they produce the same results and it took less pressure to get the pellet out of the barrel with the slower twist barrel then that would probably be the one I choose just for the fact of using less air.

  2. B.B.,
    Couple of questions for you.
    Is a longer bullet more stable than a shorter one in firearms??
    What, in your opinion, would be the ideal length of big bore air gun bullets in relation to their caliber?? e.g. .357 X .357, .45 X .45 etc. ( looking for both accuracy + knock down power)


  3. BB,
    Seems like big bores would be an ideal place to try some different concepts. Progressive rate rifling comes to mind first, but I can also see the benefit of progressive rifling depth in conjunction with that, pretty much anything to get the projectile engaged in the rifling and keep it that way. Has anyone tried progressive twist rate in a big bore?

    I was hoping something like the rogue would have had more R&D on the basics to go with its air metering system, but I know innovation usually comes from the little guys and is not adopted until it becomes competition!

    • BG_Farmer,

      I have never heard of a big bore with progressive twist.

      And, yes, the little guys are the ones who usually push the R&D. Crosman did spend a lot of time and money on the electronic valve, and they really had something, but it was too sophisticated for the average hunter who only wanted results. However, give them the results and they will ask for the programmability next.


      • I guess I shouldn’t be so hard on the rogue, mainly just frustration at unfulfilled potential. The electronic valve is a step in the right direction, at least to my thinking. Although I’d prefer mechanical regulation/control in field, electronics would be fine on a bench rifle, and programmability would be a big plus there, if accuracy were suitable.

        I’ve come to suspect strongly that the ignored factor in big bores is the different pressure curve when compared to powder. Although it is obvious and even acknowledged in passing, that difference doesn’t seem to be accommodated. Primarily, the initial pressure is an order of magnitude lower than even BP. On the other hand air can theoretically maintain a more consistent pressure in the bore. So, I’m thinking that while the big bore cannot force a given projectile into a faster twist rate through a relatively short leade like powder, it could accelerate the projectile through a slow rifled or even smooth section into a progressively faster rifled section. My theory is that this would give the most flexibility in projectile selection, assuming that the effects of over stabilization on projectiles shorter than the design targeted projectile are more tolerable than the effects of under stabilization, which I think is the case!

        • Or consider the case of the Paradox gun, where the bore is smooth until shortly before the muzzle and all the spin is imparted by a short rifled section with the bullet fully up to speed. The concept was originally developed to allow a single gun to be both a shotgun and a rifle, but I think it could have some utility in an airgun.


            • I wonder why the smooth twist design hasn’t been taken to the next level.

              They could have the smooth part of the barrel threaded and then have 2” long screw on tips that have the different twist rates.That would allow you to change the twist rate on the barrel. I guess kind of like the chokes on shotguns.

              • I suspect that the twist rate needs to be relatively slow with that short of a rifled section, so the options would be limited, plus diabolo pellets may not be as particular about twist rate as Conicals.

                • BGF
                  I believe you are right about the slower twist rate.

                  That could possibly help improve the performance of the gun. Maybe not as much pressure would be needed to move the pellet through the rifling if it was a short distance and a less aggressive twist rate.

                  I know that the FX Monsoon was a pretty accurate shooting gun. It was a .22 cal. and shot the 15 and 18 grn JSB’s around 900fps.

                  I wonder if the velocity would slow down if a regular 1:16 twist barrel of the same length would be put in a FX Monsoon with the same pellets instead of the smooth twist barrel.

                  • The big advantage of the smooth twist barrel is it is cheaper to make. As far as replaceable tips, why? Once you have the twist rate established, why change it? I can see a high powered rifle blowing that end right off and sending it down range.


                    • RR
                      I definitely was not talking about a high power rifle.

                      I was talking about air guns.

                      Maybe a person would have a assortment of tips with different twist rates from slow to fast and you could dail in your projectile for better accuracy.

                      You know my saying “Simple but effective”

                      But in this situation of trying to improve air gunning I think this would be the time to think outside the box.

                      We could be missing out on something just because somebody thinks it should be a certain way.

            • I wasn’t aware of that, thanks. Just looked it up, it looks exactly like what I was suggesting. Guess there’s truly nothing new under the sun – just a lot of things we haven’t discovered yet.

              • Jim
                What gets me is when somebody thinks things need to be a certain way.

                How did the people that BB just talked about decide that they needed to do something a different way. Look at the projectiles they came up with.

                Sometimes there has to be change.

          • Exactly, but I had some morning induced aphasia and couldn’t remember the term or even figure out how to find it, thanks! Even better, I think, would be something like a barrel that is smooth for 1/4 ? Of its length, then has a rifled section of tapering rifling depth and progressively faster rifling.

            Just for the record, all these things were tried on powder burners and worked to one degree or another, but I think the need for them was marginal in most applications. Maybe the time has come to try them on pcp’s…

            • Why not go whole hog? A smooth bore for approximately 3/4 of the barrel length, ending with a gain twist section that deepened in rifling depth as it advanced in twist? The pellet would be introduced into the rifling smoothly with an even acceleration, no sharp changes in twist to distort or damage the nose and skirt, with the smooth-bore section allowing maximum velocity by reduced drag in the initial stages of acceleration.

              The rifling could be be lapped to final profile, but that would be a lot of work and machining time – expensive. I would think cold forging would probably be the most efficient methot of manufacture, after the mandrell was made, of course 😉

              Just something I have been thinking about.


              • Jim, I think we are saying/thinking exactly the same thing except we differ on the relative length of the smooth section! My thinking is that the smooth section need only be long enough to get a good percentage of the desired velocity, leaving adequate length for very gradually increasing the twist rate and rifling depth from “zero” to the desired final values.

                I was thinking that the barrel could be rifled progressively (including the section that will be smooth, which section would simply be straight rifled) first, then reamed with a reamer profiled and tapered to make the smooth section and the progressively deeper rifling. I conjecture 🙂 it would be similar to making the chamber and leade of a cartridge barrel, but will admit that is all a guess. Making a mandrel and hammer forging the barrel is a good idea, also.

                • BGF and Jim
                  Please don’t take this as arguing But as discussing possibility’s.

                  I like the Idea of the progressive rifling but I think the smooth part of the barrel should go at least half of the length of the barrel or a little more.

                  The longer the barrel is smooth the more time the projectile has to speed up and use less energy while doing it. Then when the projectile hits the lighter slow twist of the rifling and progress to the faster deeper rifling would be better.

                  Its kind of like the bands on the projectile. There would be less drag on the projectile and less heat produced in the barrel and projectile if the smooth part of the barrel would be longer.

                  And again just a idea I’m throwing out there. Maybe there is something that I’m missing.

                  It should also be a easier barrel to make if there is less rifling to do.

                  • No arguing from my viewpoint. I want the smooth section long enough to develop desired velocity, but I also want the rifled section long enough to allow gradual progression of twist rate and rifling depth, especially if narrow lands are used to further reduce friction. The right answer is probably b/t 1/4 and 2/3 barrel length depending on barrel length…

                    Thinking about it, I believe such barrels as prototypes could be produced for a reasonable price out of easily machined 12L14, which is used by many ml/BP barrel makers. I know a couple well enough to ask them, so maybe I’ll follow up. Alas, I don’t have a big bore or a real R&D budget in the big bore industry! I wish we could try it, though, as so many of us seem to be thinking the same way.

                    • BGF
                      Maybe the barrel design we have been talking about could be tryed on a smaller scale like the small bore air guns.

                      Then try some of the already available wadcutter flat nose designs.

                      I would like to have a flat nosed pellet be able to be shot accurately to 50 yards or farther. That would be something I would be very interested in.

              • For a PCP in which “feedback” may hold the valve open longer on slower moving pellets, this may be viable.

                For a spring gun, in which the greatest impulse is the instant before the pellet starts moving, and is all “downhill from there”, having a sudden section of rifling to be engaged is likely going to generate a sudden slow-down of the pellet… More than just a choked muzzle inflicts.

                After all, you need the bore snug enough to squeeze the skirt, at least, to prevent blow-by. Now you start engraving the rifling onto the pellet to start it spinning at the point where the propulsive pressure is falling off rapidly?

                • Wufraed
                  Think about it this way also.

                  What happens to lead when it stops or hits resistance?

                  I think the skirt of the pellet would exspand in a sense when the pellet transitioned from the smooth bore to the rifling. That air behind the pellet would pressurize as the pellet hit the rifling I believe. I think it will seal better.

                • My experience is with powder-burners, CO2 guns and limited PCP, so I admit I hadn’t considered the spring-gun case. With the low velocities of airguns, it just seemed that this could work.

                  Of course, to really take off, the accuracy would have to equal or beat (not sure that’s possible) current top-end technology. That’s a tall order at this stage of airgun development.


      • Whatever happened to the electronic trigger from the early 80s that was supposed to reduce lock time to nothing and revolutionize accuracy? This makes me think that your electronic technology needs to be directed at the right phenomenon to improve accuracy.


          • RR and Matt61
            I don’t want no part of electric pellet guns right now. Especially expensive ones.

            I hope I can change my mind but I don’t think I will be able to.

            I’m only going to list one of the things that I don’t like about electric pellet guns.

            The trigger. I will take the crisp feel of a good 2 stage trigger forever over a electric switch.

            • On the one hand, I agree that I don’t like the thought of an electrically controlled airgun..every device from toaster to car has some electronic stuff inside, and guns are among the very last things that solely rely on pure, understandable mechanical principles

              However, the trigger of an electric gun is usually one of its big plus points, as it is very easy to give it a a clean, crisp&creepless feel, be it one or two stage. The electronic triggers for firearms died out because mechanical triggers can achieve the same, without need for batteries. But electronics in an airgun don’t just help with the trigger, they also increase shots per fill, decrease velocity variations between the shots etc…and when your valve is already electronically controlled, you get the good electric trigger as a freebie.

              • Mel
                I will just have to say it the way it is. I had a FX Monsoon and a Evanix Speed.

                The Monsoon would run circles around the Speed.

                First the electronic trigger was hard to tell when it would break (when the shot would go off). That made it a little harder to achieve accuracy. And I could definitely get shots off faster with the mechanical Monsoon.

                And I didn’t have to worry about battery life.

                But on the other hand I totally like the way the Benjamin Rouge valve system worked to control the shot. And I have not shot one so I don’t know how the trigger feel’s.

                And we did talk on the blog about a electronic aim system for a rifle that somebody invented. You would pull the trigger and the shot would go off when the poa intersected with the target.

                So I know there is nice technology out there for electronic guns right now. Its just not for me. And if somebody gave me a Benjamin Rogue today though I wouldn’t turn it down that’s for sure.

                I guess I’m still kind of old fashioned when it comes to trigger’s.

  4. Tom,


    As a plinker and paper-shooter, I automatically begin to think of how the Balle Blondeau design might behave in small caliber air rifles and smooth bores

    First, is the Blondeau still accurate and stable when shot through a rifled barrel?

    Second, how difficult would it be for an experienced bullet-caster to create pellets/bullets of this design in .177? .176?, .175? Specifically, I am thinking of how accurate a Pioneer BB76 might be at 10 meters or even 15 yards with a .176 Blondeau muzzle-loaded projectile. A muzzle-loaded Daisy Model 25 also comes to mind, as does a Haenel 310.

    Again, a fascinating report. Thank you so very much for writing this.


    • Michael,

      I don’t know hhow the Balle Blondeau would work in a rifled barrel, but the dumbbell slugs really made air rifles accurate.

      As far as a smallbore air rifle goes, a diabolo pellet is very much like a Balle Blondeau slug. And I did do an accuracy test with a smoothbore Diana 25:




      • Tom,

        If only I could find a severely undersized diabolo that could be gently muzzleloaded into my Pioneer BB76 or Haenel 310. As it is they are a lot of fun, but precise they are not.


  5. My thought on this is in the opposite direction. Can the dumbbell or Blondeau bullet fired out of a smoothbore airgun barrel be as accurate as a diablo pellet fired out of a rifled barrel? Then how much cheaper would it be to manufacture an airgun without the rifling operation and still have pinpoint accuracy by using a Blondeau style pellet? Would it work and would the reduced aerodynamics of the Blondeau pellet reduce the effective range over a diablo type pellet? The sport needs some serious hobbyists and even pellet manufacturers to do some research into this if not done already. This could be the next big advance in our sport perhaps?

    Fred DPRoNJ

  6. Gunfun1,
    The discussion about compatibility of oil in PCP’S has me questioning the ability to go from co2 to hpa with the 2240’s without the possibilty of detonation if other than silicone oil has been used in the gun.

    • Reb
      At the most with the 2240 you were putting a drop of oil on the tip of the Co2 cartridge to seal the cartridge. Very minimal oil on the seal or into the gun.

      The tip of the hi-pac also seals on that gasket. or the new one if you replace it. At the point and time when the hi-pac is put on the 2240 I would only use silicone oil from there on out.

      I would say any oil that was not silicone and used in the 2240 prior to the hpa would be very minimal. Maybe your first shot would blow the old oil out the barrel. So I would say it would be no big deal.

      But don’t use your old oil any more only silicone oil in the hi-pac fill valve if you fill you need to lube the internals of the gun. That’s the way I do it. But anything petroleum based is a no for me on the inside if its hpa.

  7. This post didn’t get through, so I am posting it for reader RB,


    Are you familiar with Paradox/Explora/Ball & Shot guns and bullets? I’ve wondered about a similar projectile for big bore air guns.

    I have a vintage Paradox bullet mold that throws a bullet that look like this:


    You and others may be very knowledgeable of these guns. They resemble double barreled shotguns, but are heavier, and shoot both shot and bullets. My Westley Richards Super Magnum Explora shoots 4″ groups at 55 yards (with my handloads and me behind the trigger), and throws modified shot patterns with #6 shot.

    The bullets are heavy and soft, with two bearing surfaces to reduce friction and pressure. Some bullets have pointed copper noses to reduce drag and increase penetration.

    The bores of these guns are interesting, too. The bore of my Explora is tapered, choked, and the choke is rifled with a coarse “ratchet rifling.” The technology is fascinating, and they are beautifully made guns.

    Best wishes,


    • RB,

      I am acquainted with the Paradox bullet style, but I have no experience with them. I have seen them used with big bore firearms like 8-bore and 4-bore guns.

      I haver seen pictures of ratchet rifling, but I’ve never actually seen a gun that had it.

      How interesting!


    • RB,
      The ratchet rifling reminds me of another speculation I had this morning. I’m thinking that narrower lands could be a help to the big bores, especially since the bullet has to engrave itself cold without either obturating or having massive pressure behind it. In conjunction with tapered rifling and a gradually progressing twist rate, small groove diameter driving bands and narrow land rifling would impart spin while keeping friction to a minimum.

  8. BB, me and my friends had this discussion a while ago, but since today’s post is about bullet stability I think I will ask it here anyway. We were talking about the use of lead bullet intended for pistols in big bore airguns.
    Would a .45 ACP lead bullet of short length, 200 grain for instance, work well in the following guns (considering the appropriate bore sizes for each gun): a 1911 pistol, a .44 Remington black powder revolver, a .45 Hawken black powder rifle and a .45 big bore airgun?
    In our discussions, we came to the conclusion that in spite of having so different types of actions, maybe all of these guns could eventually like the same kind of bullet and a shooter owning these guns could eventually buy just one type of bullet for all his guns.
    I have serious reservations on this. For starters, I am not sure of the correct bore sizes and twist rates for a typical 1911 pistol, .44 Remington and a .45 black powder rifle. All I know for sure is that my own Remington 1858 shoots better with .454 round balls of about 140 grs, but they are very soft, being pure lead, as opposed to what would be expected from a .45ACP lead bullet.
    What do you think on the subject?

    • Fred_BR,

      I was at the range this morning, testng pistol bullets in big bores.

      Not really. The bullets I tested weighed 240 grains and were truncated cones, but instead of 0.451 inches in diameter, they were 0.458-inches. And they were pure lead — something that wouldn’t work in a firearm. And they were not lubricated.

      But they looked like pistol bullets. In fact, they are the bullet on the right in the photo 5th from the top in this report.


  9. I was seeking fruitlessly for a reason why a dumbbell shaped bullet would improve accuracy through aerodynamics. But it sounds like it works through spin rate which makes sense, not in how it cuts through air. What I don’t quite get is the relation between spin rate and bullet weight. Usually weight is spoken of as the key variable for spinning, not length. Given that lead and alloys are universal materials for projectiles, you probably have a constant density so that length and weight are linked together. But this dumbbell shape subtracts mass from a given length, so do we learn anything about how spin is affected by projectile weigh?. It’s hard to tell because reduced weight has the same effect as decreased friction from the smaller contact surface. So, it could be that the success of dumbbell bullets is due to some mixture of less friction surface and less weight rather than just one factor.

    The Pyramidair Cup sounds pretty cool. Wish I could be there.

    I’m continuing to enjoy my daylight lamp and am noticing how white sunlight is. It also reminds me of a Buddhist mantra from the Amida sect which believes in a deity in the form of light. Devotees repeat the chant: “Whitelightwhitelightwhitelight.Sunlightsunlightsunlightsunlight.Purelightpurelightpurelight.” It has a kind of hypnotic effect and is not unlike similar practices in Christianity that are found in the Eastern Orthodox Church. We’ll see if it helps my shooting although I’m banking more on the contrast between the light and my shooting point in the dark.


    • You apparently missed the bit where the French design was used in /smoothbore/ shotguns…

      So rifling is not a factor in the design — it is purely a matter of sectional density vs “badminton bird stability”…

      Rifling could, in some way, be a detriment — you’ve added a spin which means aerodynamic drag stabilization is fighting gyroscopic precession. (the air is pushing the pellet in one direction, but precession is going to translate that to a torque at an angle to the correction)

    • Matt61 I was thinking more along the idea that the dumbbell pushes through the air and floats and stabilizes with help from the tail. A pointed bullet/pellet is subject to more resistance/energy at the tip and can cause it to move off path easier. Honestly I think that’s why the dome pellet does better in the airgun rifling, others have had luck with pointed pellets but I haven’t in any of my guns that shoot over 600fps.

  10. Sorry to disagree.
    Really sorry.
    But looking at the target for the .218 Wasp, that is decidedly NOT a tumble. That’s a YAW.
    A tumble would be extremely unlikely to even impact the target in any way, but rather be one or more of those shots mysteriously disappearing into the aether, never to be seen again. You’ll get that phenom from firing a .22 cal projectile in a .25 or .30 cal barrel. Stabilization is not an issue in that instance as there never was a question of engaging the rifling…it couldn’t have happened. Think shooting a .50 musket with a .36 ball.
    it’s gonna wander some.
    What you’re seeing here is a projectile that did engage the rifling, collected a healthy spin, but just the
    wrong spin, but never encountering a solid object after leaving the barrel.
    The key to recognizing this is the fact that they’re all on the target, e.g. stabilized, and they’re all interdicting the target at the same aspect. A tumble, even if managing to hit the target, would be at random angles and random aspects.
    But the real giveaway is that under these circumstances, to tumble, normally the projectile would have to impact something far more substantial than a single sheet of target paper…AFTER leaving the barrel. Far more substantial would include something like a resident Arkansas deer, or a Viet Cong Sapper.
    Never could do much to tighten those ping-pong ball groups from the Blurp gun:)

    • 103David I was wondering about that because the bullets had a perfect side profile in the target. I have seen this before and it just popped in my head as I was reading the comments and saw your response. When I shoot my SynRod .25cal out to about a hundred yards with RWS 25 grain hollow points I found all of them and they impacted the target almost perfectly sideways. I called it keyholeing myself but something didn’t add up because their were no signs of tumbling, not one hit any other way but almost perfectly sideways.thank you.

  11. Am I the only one who would LOVE a multi-pump pneumatic big-bore? I like my gun to be largely self-contained and easy to fix (why I’ve stuck with my 397, on it’s second valve). If made right, it would be a lot like a muzzle loader in terms of shooting experience, but easier to clean.

      • I was pretty excited to see the guy with the 30-pump big bore.
        “Among them was a father-son team of Bob and Mike Chilko, who each had a big bore gun they had made themselves. Bob shot a .398 underlever, and Mike had a front-pumper that had to be pumped 30 times for each shot. ”
        The picture and caption makes it seem like the underlever was a self-contained unit, as well. I’d definitely enjoy more info on that sort of thing. Like plans. 😀

        • Ojay,

          No plans exist for either of their guns, as far as I know. But anyone who can read and follow plans should be able to build a gu without them. These are not that complicated. Just follow the pattern of a Benjamin 392 and enlarge it.


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