Bob remember my hollow bullet AKA wing ring!!

[oldpro]

 I so wanted to pursue this and made some attempts at it that made me question ballistics and things I never witnessed before like even at 1100 fps at 4k feet no sonic boom? Everything else made a sonic boom up here at those speeds but not the wing ring as I called it.  What made me think of it again Bob was this add I just seen on FaceBook LOL. The last attempt was in a 30 cal I used a piece of alloy stock and drilled down threw the middle then carefully tapered it on its tail in the lathe I then used and old burst disc and put it behind the WR(wing ring) and shot it threw the chronograph it was doing a tad over 1100 fps though it weighed only 33 grains but no sonic boom and this is very un-scientific but!!! I could hear it tearing threw the tree branches way way out in the woods much further than anything I previously heard. I would love to test this with a lab Radar and see if my hunch is right and it carries momentum or energy far better than a conventional bullet. It was so time consuming to test I stopped and started working on the ART/Sikes valve at that time.

[dmeguy]

I wonder if a sabot of some kind could be used that would slow and breakaway soon enough to keep the sound level down.

[aceflier]

Would be able to take a core sample lol. Wierd idea indeed but looks very aerodynamic. Problem is how to get it moving? Like above maybe a sabot.

[oldpro]

Just like I did use a small disc to push it up the barrel where they separate after the muzzle.  Mind you I only did it a few times but the disk never went more than 10 feet I used it (the disc) several times.

[rsterne]

You need to Chrony it and calculate the BC....

Bob

[subscriber]

A simple hollow, through-flow projectile would have low linear drag, but its large side area would still produce significant wind drift.  This is because a hollow cylindrical projectile has a large side profile surface area, combined with a low mass density; despite its good conventional sectional density.

For the above reason, I rejected this concept a year ago, when first challenged by Matt Dubber to come up with a new high BC airgun projectile...

At the time, I considered a converging diverging nozzle interior passage; a simple cylindrical section with sharp or rounded ends; or a "wing profile" to maximize flow through the projectile.

Now, you may have a winner, if you can succeed in placing the CG relative to the side profile, such that a side wind would yaw the projectile just enough to make it "steer" itself back on track...  This probably means a slightly forward of center CG.  The principle would similar to what makes nose heavy cars better at resisting side winds than those that are tail heavy; or even BMW "50/50".

[rsterne]

Actually, the "side area" of a projectile has nothing to do with the wind drift, that is a common misconception.... The drift is proportional to the "lag time", which is the difference in flight time between the real world (in air) and in a vacuum.... There is lots of information (and misinformation) about this on the Internet.... The best books on the subject are by Bryan Litz.... http://appliedballisticsllc.com/products/books/ .... but a serviceable explanation may be found on the Sierra Ballistics website.... http://www.exteriorballistics.com/ebexplained/4th/532.cfm

The most important influence on the deflection caused by a crosswind is the BC, or more properly the Cd which varies with velocity.... This is why bullets launched at 1500 fps have a lot more drift than the same bullet launched subsonic.... In fact, most bullets have to have a MV of over 3000 fps before their drift is less than the same bullet with a MV of 900 fps....



The above chart will not only show you how important the BC is in reducing wind drift.... but also how dreadful the drift becomes in the Transonic range (Mach 0.8-1.2)....

Bob

[subscriber]

Bob, that all sound good for conventional bullets.  If a hollow cylinder is not unconventional enough, consider this unconventional projectile:

A projectile shaped like a thin double ended dagger blade, with no handle.  It would have a very high sectional density, with very little linear drag, as long as it traveled point forward.  I would be surprised if the large side area does not increase its drift due to a side wind.    I can see that due to its flat two dimensional shape, wind drift would be less when presenting its thickness to the wind, laying "flat"; and much greater when presenting its full area, when "on edge".

I don't see this as different from a large truck.  Those drift like crazy in side winds, or even blow over.  What other reason than because they have large side areas for the wind to act on?  If the same truck had the mass of the load box concentrated into a small low solid profile, I bet it would be less affected by side winds, due to the reduced area.  Am I wrong?

[rsterne]

Your arguments are compelling, as are most that talk about "side area" affecting the flight of bullets.... All I can say is that I am not about to go against decades of study on Ballistics.... There are many confusing effects on bullets, such as "Aerodynamic Jump", where the bullet yaws suddenly in reaction to a sudden crosswind (or cessation thereof) that I do not even pretend to understand.... However, every usable wind drift table or calculator, at its root, uses the Cd, combined with the SD, to create a BC of some kind.... The variation in Cd with velocity (huge increase in the Transonic) is what causes the weird looking curves in my previous post....

Perhaps your observations about the reaction of a truck to a crosswind have to do with the extremely LOW sectional density (compared to a lead bullet) and the LOW relationship of the velocity of the truck to the velocity of the wind (which could actually be greater than that of the truck).... Maybe we might see similar reactions in bullets if they were made of plastic (similar density to water, which would compare to a loaded tanker truck), and the crosswind was 1000 fps, I don't know.... Your average semi-trailer (basically an empty box) would have a much lower SD than the same box full of water (which is 1/11 the the density of lead)....  In addition, the side force of the wind is well above the traction force of the tires on the road, which is what provides the overturning force.... so tall trucks would indeed overturn easier.... If your example of the knife were spinning (to create stability and keep it flying point forward), then the drift would, of course average out as well, even if it were present.... Perhaps a better example would be an arrow with feathers.... There is little doubt it may turn slightly to face into a crosswind, but it would not FLY upwind, but continue to drift downwind with the moving mass of air....

I have never, ever, seen a wind deflection table or calculator that takes into account the side profile of a bullet (I am not talking "spin drift" here, which is a completely different subject, and occurs even in no crosswind).... If it were important, then you could have two bullets, with the same BC (Cd) and velocity that had different amounts of wind drift.... Until that is proven, I will go with the accepted methodology....

Bob

[subscriber]

Thanks Bob,

So, it is not that the side area of a bullet does not matter, with respect to wind drift.  It is that it does not matter for the typical ratios of bullet to wind speeds, and for the typical bullet shapes and densities.  If you think about it, most long range bullets "look the same", with no oddball projectile used by anyone.  At least, not yet...

That said, a lot of truisms are approximations that are "good enough", even if incorrect.  Extreme examples of this was what I was told as a kid back in South Africa.  Some of these myths were even repeated by my instructors when I did basic training, during compulsory military service:

"The 7 mm Mauser bullet is so fast that it flies dead straight out to 200 yards; then starts to drop."  What my Boer ancestors had experienced was simply that you could aim point blank, anywhere from 10 to 200 yards; and tag your antelope or Brit without any trajectory compensation. 

The Boers also believed that the bullet reached its maximum velocity at 100 yards, because at that range it would usually shoot through a Kudu broadside.  This, while the bullet would usually stop short of passing through at under 50 yards.  Their practical observations were correct, despite their understanding being completely wrong about why that was happening.  I had fun explaining to my instructors why these truisms were actually false...

Anyway, it sounds like oldpro is already shooting through-flow cylindrical projectiles.  Then he is in a perfect position to test their cross-wind drift characteristics.  No matter the theory, the main thing that matters is actual field test results.  We can argue about the theory after the results are in

[rsterne]

Indeed, when someone disputes the accepted science, it is up to them to prove it.... just like Lloyd did when a very well renowned Airgun Guru stated that the maximum possible velocity with air in a PCP at room temperature was 1650 fps, because that is the random molecular speed, so OBVIOUSLY the air cannot expand faster than that.... He did 2162, and just yesterday I did 2097 fps.... Unfortunately, the science behind WHY we can do that is still in dispute.... all we know is that we can do it.... and without any smoke and mirrors....

It is entirely possible that the science of ballistics is wrong, despite decades of study by the military and others (and they have tried some pretty bizarre shapes).... but I'm not ready to dump it without proof.... Perhaps that will occur, in the form of Travis' wing ring projectile having more drift than it should, relative to its forward velocity loss.... Bottom line is, it would have to NOT conform to the "lag time" calculations if that is the case.... and therefore disprove them....

I use existing theories, and methods of calculations until they are disproven.... At that point, I go looking for another theory that fits the data....

Bob

[subscriber]

Even if the wing ring projectile has more wind drift that its BC predicts, that does not have to imply invalidation of lag time predicting wind drift for regular projectiles. 

Just like diabolo pellets behave differently from bullets, so other classes of projectile may have their own rules that predict their behavior.  It would not mean ballistic theory is wrong, just that it may be more nuanced than what is currently understood.

[rsterne]

I disagree, it would imply invalidation of "lag time" as the science behind the relationship between wind drift and forward drag.... ie the relationship between sideways displacement in a crosswind and the Cd of the projectile.... As such, it would require a new theory to explain the measured reality....

BCs are a comparison between the measured Cd, at velocity increments, and the Cd of a standard projectile at those same velocity increments.... that ratio defined as the Form Factor.... Choose a different standard projectile and you get a different number for the BC.... However, the "lag time" is hardwired into the ACTUAL Cd, and how it changes as the projectile slows going downrange.... it is independent of the chosen standard model, or the BC calculated using that model.... If the sideways velocity and displacement can not longer be calculated using the lag time.... then surely that calculation, and the theory behind it, is flawed.... Anyways, all moot points until somebody comes up with a projectile where the deflection in a crosswind does not match that predicted by the lag time calculations based on its incremental velocity changes enroute to the target....

Bob

[oldpro]

 Bob do you think this could be cast?

[subscriber]

The core pin would have to meet the gate.  That makes it tricky, but not impossible...

[subscriber]

Attached is the image of a projectile that combines the full caliber cutting ability of a wadcutter, with the aerodynamics of a very long shallow boat tail.  It is just that the boat tail is internal:  The probable intent is to shoot it "thin side aft", so the small hole end is the nose, or high pressure side.

I have added my low-friction tiny-twin driving band idea to Matt Dubber's requirements for a 25 grain .22 cal projectile, limited to a 9 mm length.

The simple tapering through hole, with a 10 degree included angle should make it "cast-able".

I see no need to taper the "nose" or "tail" outside diameters; other than as shown for easy loading and self-aligning capability.  While a more tapered nose and tail may improve the aerodynamics, the fact that the cavity is open means that the projectile will not expand vigorously due to hydro-static pressure.  As such, to make this an effective hunting round suggests it needs a near full caliber blunt or "cookie-cutter" nose.

The tail could taper externally, but by leaving it blunt as shown below, the projectile could be loaded either way around - whichever way produced the best accuracy and the least wind drift.

Obviously, the projectile would need to be loaded with some sort of sealing disc behind it, that would drop off at the muzzle.  Don't know what such a disc might do to plastic baffles common with PCP air rifles...

[rsterne]

All these ideas are cool, and very "outside the box".... Only making them and testing them will tell the "(boat)tail"....

Bob

[subscriber]

I hope oldpro does not think I am trying to steal his idea; or claim credit for it.  However, it should be obvious by now that I am perfectly capable of generating "unusual" ideas all by myself. 

My impression when looking at patents is that almost anything I can think up has already been thought up.  While this can be frustrating, it is also a validation of sorts.  I happen to have more than a dozen US patents, with another handful in the pipe.  None of them relate to lead slinging, so I am not competing with any of you here.

The through-flow "nozzle" design below is closer to one of my original ideas; hatched about April last year.    The nozzle shaped internal cavity could be swaged; but good luck casting it with a conventional mold.

[subscriber]

Smoother flow nozzle design below:

[rsterne]

A question for you.... If the airflow reaches Mach 1 at the narrowest part of the convergence, the flow will choke.... That causes about a 47% pressure drop across the choke point (that is a condition of choked flow).... Do you feel that would be better in reducing the wake drag than an exterior boattail?....

I am adding the chart below to this post, so that you can visualize the ID at which choking would occur at different velocities.... The chart was intended to show what size transfer port is required to avoid choking inside an airgun, based on the MV, and was developed by Steve in NC.... Unfortunately, he used the muzzle velocity, which only applies if the valve is still open when the pellet exits.... The proper velocity to use in the left hand column would be the velocity of the pellet at the instant the valve closes (because the flow through the transfer port stops at that point).... and he used the speed of sound at NTP, whereas it increases at the very high pressures found inside a PCP.... However, for your purposes, where Mach 1 should be approximately 1130 fps in air (neglect the right hand table for CO2) it should give you an idea of what ID for the "venturi" will choke at various pellet velocities.... For example, if a .25 cal pellet is travelling 900 fps, the ID would have to be 0.223" to avoid choking.... If it is smaller than that, then compressed flow is occurring, and shockwaves must be forming somewhere.... so you can't rely on what your eye tells you about "normal" streamline flow, IMO....



I love your drawings, BTW.... wish I had the skills (and software) to do them....

Bob