Analysis of Slow Motion all-of-flight videos; what can they tell us? ...with examples

[Harry Fuller]

Harry,

OK, now you got my attention. Decided to shoot a tin or so 18gr in the 5.5mm. Usually I would be using 15.9gr so the 18gr is doing about 810 ft/sec. Shooting at 100m today at x10 mag on the scope, I noticed the spiraling. There was some wind so initially I thought it was wind drift but after a couple it is clearly spiraling when I starting looking for it.

Seems to start at about 60-70m and make about3/4 spiral before hitting the target at 100m. That is all +/- as it what I guess looking through the scope.

I will probably shoot 15.9gr again in future but this is interesting ...........

Now the question is ...... how do one get rid of this ?

Increase / dcrease the speed ?

The variables are many. I still have more questions than answers but am at least collecting data. The gurus may give you answers. Let's hear what they have to say.

In the meantime, as I know pellet heads' damage to be one issue, because I can induce spiraling by slightly damaging pellet heads - give your barrel a good clean to prevent pellet heads slamming through lead chips or deposits in the barrel. ( Ted found cleaning his barrel reduced spiraling ). ... Then, for 80 to 100 m shooting, raise the velocity of those 18.1 gr pellets to about 880 to 900 fps for a trial. ... and watch carefully that last 30 m of flight. Perhaps also experiment shooting across a constant wind as compared to vagrant or gusting breezes.

Until we get enough spiral data correlated to the things I mentioned in the post viz:

* group size
* pellet muzzle velocity
* velocity decay rate - drag coefficient and ballistic coefficient BC (as tested for the particular rifle and pellet).
* points on the trajectory curve as they relate to positive and negative gravity to pellet trajectory vectors
* pellet head size and shape (pointed/round/hollow)
* wind direction (head/tail/lateral)
* air density/temperature/altitude.
* and interactions between the above and perhaps other things too

- then we are left with trial and error procedures - ( unless the experts have a Deja vous moment and are willing to share now ).

Enjoy your shooting in RSA, and perhaps try to make contact with Dr Lampies Lamprecht ( and give him my best regards ).

Best regards, Harry.

 

[sgeorge]

Harry,

No gurus here, we are all learning as we go.

I had another opportunity to shoot indoors with the sole intention of determining if one of my 2 test barrels is better than a 2 groove Benchmark. The process was to shoot 5 shot groups at 30 yards. 20 groups were shot. 4 targets were shot to make me feel better. Pellets were straight from the tin and skirt sized through a bushing. The majority of the groups (16) were very good but that majority also had one shot that did not provide the desired one hole effect. The remaining 4 groups were the one hole effect that 10m guns show. There also seemed to be a randomness to the POI of these "rogue" pellets, as they were all around the perimeter of the group. I could not see any pellet spiraling. Unless my gun management is becoming sloppy, my only conclusion is that some percentage of pellets (16%), even from the same lot and prepped the same way, have some type of flaw that is not discernible to the naked eye.

 

[Wannebe]

Enjoy your shooting in RSA, and perhaps try to make contact with Dr Lampies Lamprecht ( and give him my best regards ).

Best regards, Harry.

Hi Harry,

Lampies and do talk a bit now and again. I will pass on your regards.

Thanks for your reply. Before I read this I did increase he speed o about 890 ft/sec. Unfortuantely I ran out of time but I did manage to shoot about 5 shots at 100m. I couldn't detect any spiraling. No time to shoot a group either. I will have to test more .......

I think this will now be have to wait. I know this rifle is not setupped 100% as I'm waiting for a barrel. When that arrive I will start from scrach.

Albert

 

[Harry Fuller]

Harry,

............ The majority of the groups (16) were very good but that majority also had one shot that did not provide the desired one hole effect. .................. There also seemed to be a randomness to the POI of these "rogue" pellets, as they were all around the perimeter of the group. I could not see any pellet spiraling. Unless my gun management is becoming sloppy, my only conclusion is that some percentage of pellets (16%), even from the same lot and prepped the same way, have some type of flaw that is not discernible to the naked eye.

My present surmise is that those are ones which will evolve into a spiral at about the 40 yd mark. They may well have a centre of mass axis that is fractionally not coincident with their centre of form. In which case their C of G spirals in the barrel and leaves the muzzle at a tangent to that bore spiral. That will be random in direction. It probably will cause precession and then most probably that will lead to spiraling.

Here is a classical case of a tight group at 71 yards spoiled by a pellet that started to spiral at about 40 yards.

http://img.photobucket.com/albums/v392/Kyogle/Kodiaks4shotsN2spiralflier71yards.mp4

Here is what 5 shots flying without spiral should do at 71 yards. These were skirt sized and then Yrrah rolled to batch for head size and the best for the FX Elite selected:

http://img.photobucket.com/albums/v392/Kyogle/FXElite5Kings71yardsJan2012-1.mp4

Yet still an undetected flaw in one pellet could have resulted in just another outlier. We are yet at the mercy of imperfections.

I have now figured a study design to support, or otherwise, the above theory and will carry it out when next at the farm. ...
Why the delay to say 40 yards (or further)? Well because of the pellet inertia (related to momentum) the overturning wind pressure may take some time to trigger the event. ... I have now noticed in some of my full-flight SM videos that there sometimes seems to be what I would describe as a "twitch" one way the instant before the spiral starts in the opposite direction to the pellet spin........... More to come.

Kind regards, Harry.

 

[sgeorge]

Harry,

First, what camera and associated equipment are you using for these videos?

Second, skirt sized pellets and rolled. How much variation in end point are you seeing? I seem to have some that could be related to pellet length, top of head to bottom of skirt. A <.270 length pellet ends up at a different spot than a .272 length pellet.

 

[alinwa]

Fantastic!!!

Thank you for these videos.....

Al

 

[Harry Fuller]

Harry,

First, what camera and associated equipment are you using for these videos?

Second, skirt sized pellets and rolled. How much variation in end point are you seeing? I seem to have some that could be related to pellet length, top of head to bottom of skirt. A <.270 length pellet ends up at a different spot than a .272 length pellet.

My camera is the Casio HS EX - FH 100. I think it has been superseded by other models now. The bracket that attaches it to the scope is a German Seben. Ted from Wisconsin first sourced the set-up and first described it for us on the YF. ... I have taken it a step further in being able to track pellets over the full range (when light is adequate) to about 150 yards for flight analysis.

When compared to the selection processes I used to do, inspect, weigh etc., average groups at 100 yd in best conditions, over five to ten groups, went from around 1 1/4" to 1.10" and sometimes under one inch; and though the best groups of less than 3/4" have not changed much, there are fewer of 1.50" and above.. The more than occasional wild fliers that cause those larger groups have virtually disappeared. I don't mean those caused by poorly read wind; or poorly executed called shots; and of course the best pellets used in .22 cal and now .25 cal.. I do still weigh some pellet types (after rolling)that are known to vary enough to cause low shots at long range - Baracuda .25s for example.

My real experience with .177 has only just begun with the advent of the TM 1000 (and low powered FWB 300S). So I am now working on this one rifle and the LW barrel that came with it; and getting used to an old, on loan, mechanical front rest. I don't have access locally to CP pellets so am working my way through those I do have. The first trial will come when it goes into competition with the EV 11s that our OZ team won last year's World Teams LV event with over your way.

I have not measured pellet lengths; but if there is that much variation, as you suggest, then the majority of odd length pellets would also be discriminated out during the roll test - unless by some coincidence the length between the two rolling circumferences was canceled by a proportionate difference in head circumference to produce the roll arc.

Think I answered your questions as best I presently can .......... Kind regards, Harry.

 

[herb1836]

Some points to ponder about this...

I've followed Harry's reports on the yellow with great admiration for his dedication. A couple of points...

Interesting to note that the direction of the spirals is always in oppositional rotation
to the pellet's spin direction. Right twist equates with left spiral and vice versa.
I have both L and R twist barrels and this always results. No, it has nothing to do
with water and sink holes.

The precession motion is retrograde (in the opposite direction of the spin) because a pellet is drag stabilized at the tail, rather that spin stabilized like a bullet. For a bullet the CoP (center of air pressure) is in front of the CoG (center of gravity). So a bullet (1) must be spun to fly stably, and (2) will precess in the same direction in which it spins. For a drag stabilized diabolo pellet, the CoP is behind the CoG, so the pellet does not need to be spun to fly stability (without tumbling end over end) and it precess in a retograde motion. A diabolo pellet is more like a mortar round with fins which is also drag stabilized.

One must be careful when discussing airgun projectiles since some are actually air gun bullets, not diabolo pellets. The two types of projectiles have different flight characteristics.

1. The reticle of your scope shows a great deal of movement on firing....

I've tried to get some of the members on the yellow to use a spotting score mounted about 2 feet over the rifle. The spotting scope would have more light, and be steadier so that less movement of the pellet could be detected. The idea is to be looking down the "line" that the pellet travels in its last third of the flight. The pellet's downward travel isn't absolutely linear on the last third of the flight, but close enough to be an interesting position for the camera. Grinding some Chairgun data would give you a very good estimation of the height above rifle at which the camera should be mounted.

2. How does pellet balance relate to barrel twist rates? The numbers seems to favor slower twist rates for barrels shooting our preferred pellets.

As I pointed out on the yellow you could cross-section the pellets and take a picture. You could mathematically rotate a 2D cross-section of the pellet to get a 3-D representation from which you could calculate the two spin moments of momentum. One moment is about spin axis. The other two of 2 axes are equivalent and perpendicular to the spin axis. The precession rate is a function of the pellet's aerodynamics, yaw angle, spin rate, and the two moments of inertia.

Unfortunately I don't understand the ballistics equations well enough to be able to exactly specify this relationship.

Now, for the big question. How can we make this new knowledge relevant to our shooting at 25 meters, one bull at a time?

One of the things that is poorly understood in target shooting is flyers. Assuming you made a good shot before and after a flyer, this would seem to indicated that the problem is either the shooter or the pellet?

To help choose a good pellet, look for one which generally doesn't spiral when hitting a target at 50 yards. If a pellet isn't spiraling at 50 yards it won't be at 25.

But using the camera also gives you the change to see each shot as it hits the target at 25 yards. If you get a flyer you can see if pellet ran "true" of it was spiraling. If running true the the bad shoot is most likely the shooters fault. It only 1 out of many pellets spirals, then the spiraling pellet is a "bad" pellet.

---
Hope this helps,
Herb

 

[sgeorge]

As much as we all like the videos showing pellets going straight or spiraling toward the target, they all lack any corrective solutions. Many shooters have very elaborate prepping and sorting procedures but continue to see flyers, even indoors.

First, let's define a "flyer". 2 years ago, most would have said a pellet that produces an 8, maybe a 7. Now, many would say a 9. Hopefully, that means progress at some level has been made. A quick look at our records page shows some impressive numbers. The question remains, what makes the difference, prepping, sorting, great barrels or being lucky enough to pull the right pellets out of the tin? Every time I hope that breakthrough is at my fingertips, one more test proves me wrong.

Went back to the baseline, nothing on the barrel and pellets straight out. Very nice groups, excellent targets, no fuss. It could be that the rimfire guys have the best idea, leave the ammo alone, the equipment race continues and the playing field is as level as the wallets and time will allow.

 

[herb1836]

As much as we all like the videos showing pellets going straight or spiraling toward the target, they all lack any corrective solutions.

I would agree that seeing an imperfect flight does not indicate why the particular pellet was a flier. The pellet could have been overweight, underweight, wrong head size, imbalanced, or misshapen for just a few problems. So the flight of the pellet is only an indirect indication of a problem. The number of flyers in unsorted pellets versus the number of flyers in sorted pellets would indicate if the sorting was meaningful or not.

The gist is that no pellets are perfect. It is more a question if the quality control of the manufacturing process is "good enough." This meaning that overall variation in the pellets is not he major source of error which spreads the pellets.

----- Edit 12/15

Overall the point is that the full ballistic equations have a lot of fitting constants for which we do not have values. Even with the best equipment that an amateur has, there isn't anyway to design an experiment to directly measure the values for most of the constants. So is there some way in which the ballistic equations can be simplified for diabolo pellets and can experiments be design to fit a reduced set of variables which would determine the behavior of diabolo pellets?