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Air Guns Precession from the projectile’s spin

Precession from the projectile’s spin

This report covers:

  • Start answering
  • Precession?
  • History
  • Coriolis force
  • Research
  • Am I right?

Today we look at precession — a phenomenon of external ballistics that has puzzled shooters for a long time. This report was requested by reader Yogi, who commented to the recent peep sight report by saying,

“You brought up an interesting point about the spin of a projectile affecting the trajectory of the projectile’s path of flight. Perhaps subject of a blog?”

Start answering

Well, I mentioned that the American buffalo hunters had to consider bullet drift. My picture of the Buffington rear sight reinforced it. You can see that the Buffington was designed to move the rear sight slightly to the left the farther out it shoots. This was based on a test done by the Springfield Arsenal as they refined both the .45-70 government cartridge and the rifle that shot it from 1873 to 1883. They discovered that by having several expert marksmen shoot the rifle at different distances. They found that the bullet impacted the target almost 12-inches to the left of where it was aimed by the time it had traveled 500 yards.

Buffington sight
The Trapdoor Springfield Buffington sight compensates for the bullet’s precession to the left at distance.


When a bullet flies it spins because of the rifling in the barrel it came from. The longer it flies the more it tends to precess or move in the same direction as its spin. Spin right; precess right, etc. And here is where history intersects with rifle development.


Before the development of the conical bullet AND the self-contained cartridge, most rifles didn’t typically shoot far enough for precession to matter that much. Bullets did precess but nobody paid much attention. If shooters missed their target they simply missed — end of discussion. But when cartridge rifles like the Trapdoor Springfield came about, shooting at long distances did begin to matter. As I mentioned earlier, the buffalo hunters also did shoot at 500 yards and farther, so precession did matter — FOR THOSE LONG-RANGE SHOTS.

At 100 yards the 500-grain .45-70 lead bullet (upgraded from a 405-grain bullet in 1881) precesses left  1.29-inches. At 300 yards it precesses 5.1-inches. At 500 yards it precesses 11.5-inches. At 1,000 yards the precession is almost 48 inches. As the bullet slows down, it moves farther to the side, in relation to how far downrange it travels.

I have only mentioned American rifles in this discussion because they are what I researched. Precession was a worldwide issue at this point in time, because riflemen and armies around the world were beginning to experience long-range shooting as a matter of course.

It is true that in the American Civil War there were sniper shots at distances greater than 1,000 yards that were made with highly specialized muzzle loading rifles. How those marksmen dealt with precession is beyond me, for we know they certainly had it. But the number of people who experienced that amount of precession was very small, compared to the tens of thousands of riflemen around the world that had to deal with it from the 1870s and later.

Coriolis Force

Don’t confuse precession with Coriolis Force, which is also a sideways displacement of a projectile that’s fired to a great distance. This is caused by the rotation of the earth acting on the projectile in flight — literally rotating under the bullet while it’s in flight. Compared with precession the movements are small. Coriolis Force does act on all ballistic projectiles, but it only matters when the distances are huge. Naval cannons that shoot many miles have to take this into consideration, and they also have to consider where they are on the planet, as the effect changes with changes in latitude.

Field artillery must also take Coriolis Force into account, but since they are less mobile than ships they can use lookup tables (or software today) for the locality where they are on the planet.

Coriolis force also does affect pellets in flight, as does precession, but when your target is only 10 to 100 yards away, who cares? Of all the airgun shots ever made, perhaps only the ones like Ton Jones’ world record 2058-yard shot really had to consider it. And even Ton didn’t have to consider it because he used the tops of trees standing on mountain tops as his aim point. He was using the greatest holdover in airgun history and it no doubt included some correction for precession and even Coriolis Force.

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I did some research online about precession and here is what I discovered. The physicists who discuss precession don’t agree on its effects any more than we who are the great unwashed. They simply speak to one another in formulae and terms I can’t understand, as they argue the same things we do. 

Am I right?

Readers, I don’t even know if all that I just told you today is correct or not. It appears that the Trapdoor Springfield barrel has a right-hand twist (and that is another detail that’s difficult to find) which would mean the bullet would drift to the right — IF what I told you is correct. The 1903 Springfield DEFINITELY has a right-hand twist barrel, and yet its Buffington rear sight is also calibrated for a left-hand drift. And I found a few physicists who argued that a right-hand spin should result in a left bullet drift.

Springfield 1903 sight
Buffington sight for 1903 Springfield is also adjusted for left bullet drift.The faster bullet means the rifle shoots much farther and the amount of the sight’s correction for left bullet drift is harder to see.

What I know for CERTAIN is that Springfield Arsenal did not calculate anything to regulate the Buffington sight. They TESTED the rifle and ammunition at different distances and calculated the drift based on those findings.

Many of you think I should test air rifles for accuracy by clamping them in a vise. I have resisted doing that all these years for this very reason! And, the ONE TIME when I shot a rested AirForce Edge target rifle at the same time and at the same targets that John McCaslin shot from another Edge rifle that was clamped in a vise, my groups were essentially identical to his both in size and placement. So, clamped rifles? Bah!

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.

80 thoughts on “Precession from the projectile’s spin”

  1. B.B.,

    The correct answer is all of the above!

    It all depends is the only truly satisfactory answer given the variables in the real world that impact a projectiles precession.
    I do know a way to feel the force(s) involved. If you have ever watched a spinning top or held a spinning toy gyroscope by the ends or a bicycle wheel by the hub ends while it is spinning and tried to move it out of the spin axis you have seen/felt the force(s) involved.


  2. BB,
    I am trying to decide whether those ballistic engineers at Springfield Arsenal established their testing tables for drop/drift with a hand held rifle, a clamped down rifle or a barreled action, bolted to a bench. My expectations for engineers would be with the bolted down barreled action (thereby minimizing variables), but I’m no historian. But I am also quite sure that it was a repeatable experiment!
    Thank you for running the bolt blog yesterday. I am very tempted to started looking for a smooth bore for some dart shooting. I suddenly feel more enabled.
    Thanks again for what you do and how you do it.
    Take care of yourself.

    • billj,

      From what I can discern from what Tom wrote it seems they shot the rifles then plotted the curve accordingly. They must have done it several times to get that consistent data in the History section: “At 100 yards the 500-grain .45-70 lead bullet (upgraded from a 405-grain bullet in 1881) precesses left 1.29-inches. At 300 yards it precesses 5.1-inches. At 500 yards it precesses 11.5-inches. At 1,000 yards the precession is almost 48 inches.” Given a government budget they probably had the rifles shot from a sandbagged position.


      • Siraniko,

        I’m impressed at the level of technology they had then. Those engineers are heads and shoulders above any average gun enthusiast today. Indeed, I suspect that they could hold their own if dropped suddenly into the future, that is, today.


      • BB,
        Thank you.
        I assumed that the testing would be with something other than hand held, but your Edge test comment should have kept me from assuming.
        Testing tells us what it does and then it is up to us, to figure out how to explain the reason why.

  3. B.B.,

    “And I found a few physicists who argued that a right-hand spin should result in a left bullet drift.”
    You will also find a bunch of powerful propeller driven aircraft pilots that will tell you that there are FOUR LEFT turning tendencies which require FULL RIGHT RUDDER to counteract on power application, one of which is propeller disk induced precession; especially in tail draggers.
    Japanese ZERO pilots need not apply as the ZERO’S propeller spun counterclockwise (as viewed from the pilots viewpoint) while taking off or flying.


  4. Wait, right hand, left hand… I’m confused. Is that sight calibrated for left or right drift?
    The rear sight moves to the left as it is raised. That will bring the POA toward the right. If the precession is to the right, right hand drift, then the sight is calibrated for that right POI shift, no?

    I wonder if a little “Kentucky cant” (must be western Kentucky) would also compensate for such drift.


    • Berserkeley Mike,

      If the rear sight moves left doesn’t point of impact go to the left? I think it’s when the front sight moves left that the point of impact goes right.


      • Yes, rear sight moves left and point of aim moves right, so relative to that the POI moves left.
        But in this case the projectile is drifting right on it’s own, so one wants the POA to track that, otherwise it hits “too far to the right”. So to bring the POA to the right to match that (rear sight moves left).
        Sight goes left, aim looks right, gun points left but bullet eventually flies right. And my head hurts.

  5. Hi everybody,

    these seem to be pretty complex topics and I’m not sure I understand them fully.

    I would have expected the bullet spin to affect the trajectory mostly due to the Magnus effect (interaction of the spinning bullet with the air; example here: https://www.youtube.com/watch?v=jLDxUWTeDnE).

    But as we don’t live in a perfect world, a bullet also does unwanted movements like yaw (https://www.abaintl.us/yaw-precession-and-nutation/) which interacts with the spin so that has an effect too.

    The Coriolis effect is a weird one too, intuitively. Yes, the Earth is spinning, but so are we and everything else on it. You might think this shouldn’t even make a difference to the bullet relatively speaking, but it does.

    But it’s still a great excuse when you miss your 10 meter pistol shot. “Oh, must be that Coriolis effect again!”.


    • CaptKlotz,
      Not only that, but why would the bullet prefer to go in one direction and not the other in the absence of wind?
      You would think the bullet spin force would be equal and opposite all the way around?

  6. Clamping them in a vice.
    If someone can place a shot in the one hole every time more power to them. But, what if you are not an expert and the pellet fails to go into the same hole every time. Was it your fault or the rifles?
    Clamping it down should tell by eliminating the shooter. If it’s possible to put it in the exact same position after removing it to cock and load it.
    My belief is, if the rifle does not put pellets through the same hole when clamped down, it simply is not accurate and no amount of fussing around with hold, trigger pull or shooter concentration will help and you would be wasting your time. It’s a plinker.
    Now I’m assuming the exact same ‘Quality Pellet’ with a good reputation is used. It will obviously change POI with another type of pellet.

    It does not matter that the hole is not true to the barrel aiming point. Sight adjustments can be made to compensate. And of course, corrections would need to be made for distance variations.
    I just don’t want to waste hours or days trying to make the most out of an airgun when nothing will help.

    Now you can obviously spend days, and lots of cash, trying every pellet ever made in various weights and hope to find one that will shoot straight at a given distance, but that is an entirely new challenge that may never be successful. I would do research on the internet first for someone who has, but then again it may only work in ‘His’ airgun not yours. Not a bad idea before you even buy one. Rant over.

    Can we assume that all these “Outside forces” would remain somewhat constant in a single shooting session and be taken into account for sighting in?

    • Bob,

      You need to read the book “The Bullet’s Flight From Powder to Target.” It was written after 37 years of trying to figure why bullets don’t all just go through the same hole and Dr. Mann built a 5,000 pound “shooting Gibralter” bench that was anchored to bedrock, with his rifles and barreled actions clamped to it. He shot inside a 100-yard-long canvass “tunnel” that was shaped like the trajectory of his bullets. He had Harry Pope make barrels for him that he tested in all sorts of ways.

      And he never figured out anything for certain. In the end he committed suicide while working on his second book that was never published.


      • BB,

        This guy you mentioned made me think of Annie Oakley. She was able to repeated put bullets through roughly the same target hole, or so I’ve read. Of course, her shooting distances were closer.

        Cool article topic, by the way. First I’d heard of it.


    • Bob M,

      I think I understand what you are trying to say in your rant. My Webley Service Mark II is a plinker. I have put many different pellets through it and have never been impressed with the accuracy exhibited. On the other hand my even older FLZ with one particular pellet is incredibly accurate.

      If you take note, BB almost always uses more than one type of pellet in an airgun in his attempts to determine what is best for that particular airgun.

      Clampiing down some types of airguns may work; but would not work with sproingers, hence the “artillery hold”. Even then, there are variables that will affect a projectile’s flight before it has exited the barrel. Read Bob Stearn’s reports on such. (https://hardairmagazine.com/category/ham-columns/airgun-technical/)

  7. When I was “eaten up” with Vintage Military rifle match shooting I saw shots from a right hand twist rifle shooting high and right of previous charges when I bumped up charges in testing. Now British Enfields which are typically left hand twist would go left. These loads were for matches shot at no more than two hundred yards so I can only speak to that distance. I would adjusts my handloads not only for group but to aid in sighting in windage wise with some rifles as wartime production was not always conducive to precision.

    • Decksniper,

      You just described my experiences with trying to master my two springers. I’m having to relearn how to shoot a rifle! It’s a challenge, but it’s fun!


      • MiTurn

        Shooting is a life long thrill for me. Been doing it for 79 of my 85 years. I am blessed to have been exposed to gun safety and guns at an early age. Most of this time was with many kinds of powder burners. Airguns are just as much fun and very convenient for me. They are also almost as accurate at long range as Ton has proved.


  8. I very much enjoyed reading this blog and the comments.

    As a teen, I do not recall having to compensate at long ranges when shooting groundhogs. It is true that I was using rifles of much higher velocities and the typical long range was between 300 and 500 yards.

    I do recall spotting for my father during one extremely long range shot with a .25-06 at a groundhog across a small valley where the initial shot was about six feet low and about six feet to the right. How much was due to gravity and wind drift, I have no clue. On about the sixth shot, he hit the groundhog. It was far enough away that the hollow point bullet had lost so much energy that it did not expand as it went through. This type bullet would literally blow a groundhog’s head off at 100 yards.

    With airguns, I am only now being able to effectively reach 100+ yards. I watched the video of Ton’s long range shooting. So? How big was the target? Where did he hit the target? Do not get me wrong. That is quite a feat, most especially with an air rifle. It is just that I am still more impressed with the Pepsi Challenge.

      • Siraniko,

        The area between where Ton shot and the 3-foot by 3-foot steel plate that was his target is so rough that it either takes a horse or a 4X4 trail vehicle to get to the target. All the ranges in that sector have to be shut down when that happens and Ton told me it could take a long time (over an hour) to make the trip. They paint the steel plates the evening before and score them through several spotting scopes during the event.


    • RidgeRunner,

      That is why I read BB’s articles. Not just what is the topic of the day, but all the comments that follow. It’s all part of my airgun edjamacation.


  9. Well BB,
    I am going under the assumption that it is entirely possible to put 10 shots into the same hole when everything is just right, and I believe you may have done that in competition? Perhaps I should be looking into the best competition airguns to find out what “Just right” really is.

    Is it simply a fact that accurate shooting can only be achieved when every single part of the airgun is precision made just for that purpose and reflected in the cost, as in competition airguns? And every pellet used is exactly the same and identified to be the best in that particular airgun and the shooter is an extremely talented competition shooter or highly experienced?
    Would everything sold for less money be a compromise for accuracy, unless you just got lucky, and you literally get what you pay for? A bigger hole.

    I’m beginning to believe that a costly airgun will or should be capable of giving you a single ragged hole and the lower priced ones will give you a small to larger group and only lots of tinkering may change that.

    Practice can’t fix an inaccurate airgun, but then again, it might help break it in to shoot better. Too many variables for the average shooter and we all hope for the best and press on. The higher the cost, the bigger the smile. 🙂

    • Bob,

      I did put five pellets through the same hole (a 0.0-inch group) at 25 yards one time. I think it may have been a fluke (they have to go SOMEWHERE!). And Harry Pope did put ten bullets into a 0.2-inch group at 220 yards once. His was probably legitimate.


      • B.B.,

        “I think it may have been a fluke (they have to go SOMEWHERE!).”

        THAT is the concept that keeps me shooting!

        The Dark Sider shooting as Weak Sider:

        Last evening using a NRA #A17 50 FT. Small Bore Rifle Target and shooting my SIG ASP20 .22 caliber at 30 yards while shooting 30 JSB EXACT JUMBO pellets inside the black of one rondel.

        I know it was a FLUKE! Why?

        1. Springer
        2. Off Side
        3. Unrested
        4. I’m not that good shooting LEFT

        I didn’t think once about PRECESSION!
        All of my concentration was on repeating my Cheek Weld and avoiding cant.

        It was, however, much FUN!


    • Bob M-

      In a perfect world, perhaps it would be true that more money equals ‘better’ results. I mean, it’s certainly true for cars, rookie NFL quarterbacks and fancy restaurant meals, doesn’t it?

      Regarding guns in general, it pays to remember precision, accuracy and reliability. Achieving all three can be difficult. Barrel harmonics are the reaction to the projectile getting up to speed and exiting the muzzle. Does the barrel react the same each time and does it return to the same position in the gun’s frame or receiver?

  10. BB
    So the bullet is spinning right. We know bullets don’t shoot “flat”. We are shooting for a platform (earth) that isn’t flat. All at the same time our platform (earth) is spinning. Wow. Now my head is spinning.
    Now a question, has there ever been a gun with straight grooves (not rifled) to try and keep a bullet straight? I know wouldn’t work per say, at least for much distance, was just curious if it was done.


  11. BB
    Maybe someday you (or someone here in the know) can explain all the different rifling out there. I have heard of button rifling, Polygonal Rifling and more. Oh and the famous Marlin Micro Groove Rifling (which I do like). Then, although it’s not a rifling on the barrel, you have the rifled bullets (rifled slugs) for shotguns. Do they actually spin? It’s been debated many times but I don’t know the right answer. Oh and don’t go too far or we get into finned projectiles. No rifling needed.
    UPDATED: Geez, looks like your above link answers most. Thanks


      • BB,

        Good. I’m considering getting one of those Gamo .22 “shotguns.” I’ve read your reports about them, but they sure get great reviews. And reloading the shotshells might be fun to experiment with. That being said, it is an unrifled barrel that can also shoot .22 pellets and I’m curious as to how that impacts accuracy at, say, 30 yards. I guess I’ll soon learn.


  12. B.B.

    Thank you! Excellent report.
    Here I thought we would be talking about high and low pressure surfaces on the projectile.
    Are most airgun barrels clockwise rifled?
    I understand that if the wind is blowing from a certain direction, it can “catch” the direction of the spin and increase the deviation.


    PS In one of your older articles you mentioned that a pellets is spinning faster round and round than it is in making forward progress. That blew my mind!

    • Yogi,

      Yes, most rifling is right-hand, which is clockwise from the shooter’s perspective. But the Brits rifle many barrels counter-clockwise, or they would say anti-clockwise. And Harry Pope rifled his barrels that way, too.

      Yes, the wind will influence the path of a projectile. Not just sideways but up and down, too.


  13. What about the effect of air density ?

    Following are my personal thoughts: At the top of a projectile’s rotation, the air is slightly less dense and presents less friction than at the lower part of it’s rotation. Here it bites the air harder and therefore paddlewheels sideways as it flies along.

    I know that similar stuff happens with propeller driven boats. For example, when one gives a short burst of backwards power, the boat’s back end noticeably moves sideways, as well as the boat slows down, which is rather useful for parallel parking, like alongside a pontoon in a marina. 🙂

    • You are 100% correct hihihi, I know first hand that it is true. Even more, I believe that the propeller would move in a spiral fashion if it were not constrained in the vertical axis by the hull. Then again, I don’t really know.

      • Henry_TX,

        may I trouble you you to elaborate on your first hand knowledge please, for example, do- or did you handle boats?
        Oh and, what do you mean by “I don’t really know”?

        • Hihihi,

          Sorry for the late answer but I was on the road. Yes, years ago I had a series of sport boats – you probably heard about the boater disease named ‘two-footitis’ when after some time you ‘need’ to upgrade to another boat two feet longer. My boats were all single screw so I experienced the phenomenon you mentioned: when going in reverse the prop pushes the stern to one side. It can be very useful when docking, if you are on the right side, and it makes thing very difficult on the other side.

          What I meant with my second comment is that I assume that if the propeller could move freely in two axis – vertical and horizontal – it would be tracing a spiral. As it is, the hull limits the vertical movement so it pushes sideways. However, this is just a product of my imagination – I do not know if it is the case.


          • Henry_TX,

            see my reply to hihihi about Prop WALK for boats.

            I covered the four Left turning tendencies in aircraft in one of my early replies above.

            In a Bearcat F8F or T-28 Trojan you could actually torque roll the aircraft off the runway. On runup if you applied full throttle with the A-1 Spad you could compress the main mount Oleos enough to cause the prop to dig into the ramp! tohttps://en.wikipedia.org/wiki/Oleo_strut


            • I can only imagine what the torque of those radial engines could do! A good friend, pilot and instructor, was telling me some time ago about the problems with the F4U Corsair when initially released.

              Thanks Shootski, as always is good to hear from you.


          • Captain Henry_TX,

            thanks for your reply.
            Yeah, I know what you mean by it’ll work better on one side than the other. That’s when it’s handy if one can spring alongside, eh?
            (using a rope from the front of the boat to stop it’s forward movement, so that one can then drive the back end alongside by steering into the jetty, pontoon or whatever one is trying to parallel park next to – boats typically steer from the back)

            As for your idea for the effect of a non fixed propeller shaft, wouldn’t torque be the overwhelming force, you know, like a single propeller aircraft that has lost it’s wings, elevators and rudder and with reverse thrust engaged?

            I guess a submariner might know more… 🙂

            • Oh yeah, dock lines are the mariner best friends when docking to any larger object. My last boat was a 30-foot Catalina sailboat. When the wind was not cooperating good footwork and fast line handling was needed!

              And, you are correct about the submarine (or torpedo) but usually they use contra-rotating propellers to cancel the torque. I can see a can of worms there so I better quit now. LOL!


            • hihihi,

              Propeller aircraft generate reverse thrust (BETA range) by changing the pitch of each propeller blade; i know of no fixed pitch propeller aircraft that can reverse the engine/transmission to generate negative thrust.


  14. Wow! What a can of worms, both right and left handed. I really enjoyed the article as well as the comments. There is so much knowledge in the group! I never stop learning and that makes it fun.

    A couple of lose comments which I think are true, but could be wrong.

    – When changing charges (as in PBs or regulator/hammer setting in a PCP) not only the trajectory with a given pellet/bullet changes vertically but sometimes horizontally. This means that precession is always present to a certain degree.
    – A spiral trajectory can place the POI left or right of the POA, depending of the distance and speed and not on the twist.
    – Projectile yaw is affected by shape, weight distribution, rotational speed speed and external factors(wind). It is always there, and it enhances the other effects.
    – And the most important, with my poor eyesight and shaky hands, all of this is just academic to me, but very, very interesting. Keep it coming.


  15. “Naval cannons that shoot many miles have to take this (Coriolis Force) into consideration, and they also have to consider where they are on the planet, as the effect changes with changes in latitude.” This sentence led FM to take a deep dive into a Rabbit Hole of large projectile ballistics, reminding him of a notable naval-gun-to-naval-gun duel which still fascinates even in this day of “smart” projectiles.


    Fair warning: your mind may drift as you wade through this very comprehensive examination of the subject and your brain may explode in the process. Add plunging fire to the equation to further complicate matters and you will come to the obvious conclusion – as did FM’s shards-of-knowledge-riddled brain – that ballistics and targeting are complicated matters!

    • FawltyManuel,

      Thank you for that link!
      ‘ “Naval cannons that shoot many miles have to take this (Coriolis Force) into consideration, and they also have to consider where they are on the planet, as the effect changes with changes in latitude.” ‘
      Back when the guns on Naval Ships were smooth bore they were called cannons now that they are rifled they are called Rifles…confusing huh!
      I learned in Naval Science that when others are shooting at/near you that the cause of the bad things happening are most always directly the result of that shooting!

      Occam’s razor

      (In philosophy, Occam’s razor (also spelled Ockham’s razor or Ocham’s razor; Latin: novacula Occami) is the problem-solving principle that recommends searching for explanations constructed with the smallest possible set of elements.)

      If HMS HOOD had exploded any other time i would go for the accident in a turret lift/magazine as the probable cause. After all three other British Ships-of-the-Line had similar sinkings and the design changes only reinforced a poor design.


      • You are welcome, shootski. If you want to go down into more Rabbit Holes on the subject, navigate to this link. http://www.hmshood.org.uk/hoodtoday/2001expedition/hood/wreckbow.htm

        Learned that examination of the wreck indicated the bow section likely exploded as it was going under, which contributed to the tragic almost 100% fatal casualty rate. There is a very moving part on one of the web pages about having survivor seaman Ted Briggs help place a memorial plaque by the wreck.

        The shooting skills of those gun crews back in ’41 never ceases to amaze FM. Now a lot of projectiles will do all the hard targeting work and it is almost impossible to miss with them, though no doubt yours truly would somehow manage to accomplish that…imagine someday having “smart” pellets that never miss – one imagines there would be NO fun in that!

        • FawltyManuel,

          Great linked report!
          I have been interested in the big ships since i was a youngster. Built and later M-80’d many Battleships and Cruisers!
          With No loss of life.


  16. There are so many shooter adjustable variables today that it is overwhelming on the more complex rifles. You can switch out barrels for different twist rates, vary velocity, vary the pressure and impulse duration of the air. That doesn’t even cover switching calibers. It seems to make for an almost infinite number of combinations. And, look at how many I variations in pellets and slugs we have available today. I think you could spend years playing with variables on just one gun.

    David Enoch

  17. Well it’s good to see that everyone is trying to grasp the complex forces involved in projectile ballistics.
    Precession isn’t quite easy to explain, but maybe easy to understand.
    Recall the grade-school science demonstration of a child sitting in a swivel chair. The child is holding the ends of a bicycle wheel axle horizontally in outstretched arms as someone rapidly spins the wheel.
    As the child gently changes the axle’s horizontal angle, strangely the chair begins to swivel. This “gyroscope effect” is precession. How does it work in a firearm? The bullet is the wheel, spinning “horizontally” as it exits the barrel. What no one mentioned is that the bullet also “yaws”. It changes its head-to-tail angle in relation to the bore of the barrel, (the child changing the axle angle) and just as the wheel forces the chair to swivel, this force (the very definition of ballistic “precession” ) can cause the bullet to begin to rotate around it’s center of mass.
    (not just spinning on its axis, but the entire bullet rotating slowly around it’s otherwise straight-line path).
    If you can get behind a slow-moving pellet that has a bad case of “yaw” and precession, it looks like it is spiraling as it flies to the target. You can imagine, even as the bullet is “corkscrewing” around its otherwise perfect flight path, depending on when it strikes the target, it may hit to the left, (or to the right), or high, or low.
    Not all bullets precess – because not all bullets yaw. Longer “spitzer” bullets tend to yaw more. Very short diabolo pellets will yaw less. Yaw is caused by any unequal forces the projectile experiences as it exits the barrel.

    • Rocket Jane,

      Welcome back! I think I have actually have seen that demonstration. Maybe on the Mickey Mouse Club? Or Mr. Wizard?

      At any rate, thanks!


  18. As far as i can see. That Buffington sight is made to deal with a right hand drift, not left.
    As elevation increases, the rear sight moves left, causing the aim point to move right (to where the bullet would be landing).

      • Hi Tom. What im thinking is-
        When the rear sight moves left, assuming the rifle doesn’t move, the point of aim will appear to move right.
        The shooter then compensates by moving the rifle left, to put the point of aim back on the target.
        So yes, as you say, the point of impact of the bullet moves in the same direction as the rear sight.
        So that sight gives left hand compensation as range increases, counteracting a right hand drift of he bullet.
        Thats how it appears to me anyway.

        • Ian UK and whoever else this may concern,

          move the gun, not the sights.

          At the moment we shoot, the following four points are fixed on the aiming line!
          1. the shooter’s aiming eye
          2. the gun’s rear sight
          3. the gun’s front sight
          4. the target

          Obviously, when we adjust the rear sight sideways, we’re moving it sideways only on the gun, not on the aiming line.

          Having made the change, we raise the gun again to take aim and line up those four points again. So, the gun’s sights are back on the aiming line, but the gun has moved relative to it. Pointless if it hadn’t. 🙂

          We moved the gun.
          We moved the gun at the rear sight not the front sight.
          The gun rotated a little around the front sight.

          What seemed like moving the rear sight leftwards on a stationary gun, is the same as moving the gun’s rear rightwards on stationary sights.

          Here’s how I picture it: the aiming line is a taught wire from which the gun is suspended by it’s sights. Only the rear sight is moveable on the gun. 🙂

          Now imagine, making the barrel point further left… get it? 🙂

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