AusVarmint

I have often questioned the validity of the view that 9:00 o'clock wind causes diabolo pellets to deflect to down and right from a right twist (clockwise) rifled barrel and high left when influenced by a 3:00 o'clock wind. This is the common wisdom in the powder rifle fraternity and which is based upon ballistic theory of pressure gradients in the boundary layer of the bullets, influenced by the so called yaw of repose interacting with pellet spin; and upon their own shooting experiences, particularly with rimfires. ...
However, it has been contrary to my experiences in respect of diabolo air rifle pellet behaviour which has consistently indicated to me that the vertical displacement has been right and up for a 9:00 o'clock wind and down and left for a 3:00 o'clock wind.

This farm trip I took the opportunity to test and compare the behaviour of the diabolo JSB Exacts with a new .22 JSB 25.4 gr somewhat bullet shaped pointed test version of the round headed JSB Monsters, the Monster Straton, which are tending strongly towards a bullet shape. This tendency is even more evident when the pellet has been squeezed through a choked barrel as in my BSA.

Firstly the two .22 pellets being compared: The "bullet" 25.4 gr Straton to the left and the diabolo shaped Exact to the right.



The wind was blowing consistently from 9:00 o'clock as can be seen by the two wind flags ( the second is located in the old cultivator ) in relation to the target which was the frying pan hung on the white tree. The range is 60 yards to the tree from my shooting bench back in the shed. (Many starlings have done the gravity drop from the knot holes and limbs of that tree. It is reserved for rosellas when nesting ).



Although consistent in its direction the wind was considerably varying in strength which was ideal for the study at hand. Thus the two groups could be registered with each shot being fired with the wind at a different strength to show how the wind affected the vertical (and lateral)displacement according to its strength. Of course no allowance was made in sighting to compensate for the wind as that would defeat the purpose of the study.

The rifle was sighted for the heavier, more bullet shaped Stratons. They form the lower group. The diabolo Exacts formed the higher group.



The results indicate to me that the more "bullet" shaped Monster Stratons did deflect lower (and to the right of course) as prevailing wisdom suggests, and further from the POA (centre of pan) according to the wind strength.
To the contrary, the diabolo Exacts deflected higher (and right) according to the wind strength and according to my past experience.

The Monster Stratons also seemed to drift a little less in the wind - perhaps indicating a higher BC ( which I have yet to determine ).

I also shot this target (below) on the stand (beside the tree) with the quarter bore 0 .25 cal BSA Hornet and Exact .25 King diabolos and it too is in accord with all the others I have shot over the years - deflection right and higher and reflecting wind strength:



For any who are interested in the Monster Stratons under test; here is the new pellet compared to a revised version of the original Monster round headed pellet:



I am not party to if and when it will be or has been released.

I am not finished testing the Monster Straton 25.4 gr pellets but it is showing a lot of promise with 1/2" groups at 50 yards in good conditions and no signs of yaw on targets at MV as low as 750 fps. ...

The above study is open for questioning by others who may support or refute my conclusions that there may well be dynamics that discriminate the behaviour of waisted pellets from "bullets" in the context of the above study as well as in many other respects . ................ Kind regards, Yrrah

Thankyou for interesting post... An excellent read -

David.

It certainly was a very interesting read Harry.

I also have an opinion that the amount of the vertical displacement is also calibre dependant. Namely, that in the smaller .177 calibre, it is almost non existant in either direction.

I had not encountered the reverse effect as you had, since I almost exclusively use .177 calibre, and all of my range work and tests are are with that.

Bravura, for yet another myth buster.......

GS

I have taken the liberty of alerting other Field Target shooters around the World to your assertions, and of course crediting the source to you. The ensuing discussions should be entertaining, and enlightening to say the least.

Many thanks for your work. I hope you are agreeable to my informing others of your conclusions based upon experience and testing.

GS

greyskull wrote:I have taken the liberty of alerting other Field Target shooters around the World to your assertions, and of course crediting the source to you. The ensuing discussions should be entertaining, and enlightening to say the least.

Many thanks for your work. I hope you are agreeable to my informing others of your conclusions based upon experience and testing.

GS

Thank you GS. I have been away in The Outback for over a month camping and seeing the wonderful explosion of wildflowers following all the rains we have had this year. My wife's camera has been running hot snapping the flowers and emus and other birds and wildlife. So, my apologies for not responding sooner.

I certainly do not mind that you have passed on my report as I know you would have done so in the most ethical manner. ... As I only write and read on a very limited number, basically three, of forums, you might like to pass on any worthwhile input from others who have informed relevant material with supporting data. It could be added here perhaps.
I have noted what you have written in regards to the .177 cal. I must note to repeat the process with my very precise FWB 300S .177 when conditions are suitable on a future visit to the farm.
My very best regards, Harry.

Yes its good to stop and "smell the roses" on occasion.

The climate over here has changed significantly since you posted, and I have had a project or two of my own to test out.

One is continuing the building of a "Density Altitude" and Absolute Density calculator for FT shooters, that will allow a turret value to be quickly arrived at to compensate for changes in Density Altitude. Particularly relevant for Air Rifles I think.

The other is testing out the prototype pre-production model T50B FT scope from Falcon Optics. It is not quite in production yet, but I can say it is going to set a new benchmark for affordable quality. We've had a few problems with scope parralax shift in recent models touted as FT scopes, and this prototype puts the lie to the assertion that all scopes shift parralax due to temp change and lighting changes significantly. Am enjoying this testing immensely.

Your own posting over the years has been assimilated into my pellet preparation routine to some extent, so I thank you for that generosity of spirit.

Be well.

GS

That is interesting GS. I have good success using the altitude/ pressure/ humidity environment facility of Chairgun for my purposes. But not having a pocket computer I rely on printout that are not necessarily real time based.

The scope too sounds interesting. I may be in line for another scope in a couple of months and may hang off to see what the Falcon you write of offers. Thank you for staying in touch on this rather quiet forum GS. ....... ( Edit that is probably a high power 40X 50mm scope and not really suited to my needs ).

I polished the heads of some JSB Exacts but did not find a noticeable difference. Still, 27 to 45 fpe and 15.9 gr to 25.4 gr pellets may obscure any change. They are pretty slick anyway.

Kind regards, Harry.

Yrrah wrote:.......Thank you for staying in touch on this rather quiet forum GS. .......

And my thanks to both of you.

It's always interesting..........

regards, curan

Cheers..........all good.

Harry, the Falcon is a big one. It is a 10-50x60 Side wheel model. Lighter than the big Nikko Sterling Diamond sportsman 10-50x60 and much clearer. The T50B FT model prototype I have is the one with the wire reticle, and the BR and long range models have the glass etched reticle. I feel we are getting the better of the deal with the clarity of the optics. Taken back to 10x mag I have never looked through a clearer and brighter scope, and I had some nice Jap glass Tascos in the early days..........

Horses for courses, it may not suit what you do being made specifically for Field Target, it certainly is big and not what you would slap on any old hunting gun. I found the field of view to be extremely narrow, and that took some specialist mounting to get aligned with the bore on its optical centre, I ended up custom epoxy bedding the mounts because of its narrow FOV.

It does range find extremely well, and IMHO you could dispense with a laser range finder out to 200 yards if you wanted to........just using the parallax adjustment to find the range. First time I have seen that in an "airgun scope".

On the original subject of the thread:

One or two UK shooters found the subject interesting and did their own testing,.......finding the reverse to your results.

Thus might point to an effect of the different hemispheres we are in, and may even vary with distance from the equator. (direction of laminar flow in different hemispheres theory) Although I would not have a clue why it would differ, it certainly would be good to nail down again as I have not seen it happen here in NZ or while shooting in South Africa with the .177 calibre. (Sea level in NZ, 4500 ft altitude in SA) It may be an effect that becomes more pronounced with calibre size, and the tilted elongated oval that we are taught applies with smallbore target may not apply significantly in .177 with pellets of such insignificant mass.

Altitude Density:

It is the problem with most ballistic calculators that they rely on you "maintaining a zero" and all environmental adjustments you make will require you to subsequently rezero for the ballistic output data to be accurate.

I found that atmospheric shift occurs most of the time when you do not have the facility to rezero (like in the middle of a match). I wished to devise a simple technique to adapt a ballistic table "on the fly" taking into account the change in pellet speed that occurs over the trajectory as the air density changes.

The simplest I have devised at the moment could be described as:

@100 yards: 1 inch shift in POI = a change of 1000ft Density Altitude = a change of 10 deg Celcius

Typically one might see a shift of this order if the temperature was raised by 10 degC, and Humidity remained stable (humidity has a very small effect by comparison to Temperature at a stable location where you have established a "zero") and altitude remains stable.

I would be pleased if anyone wishing to field test this idea does so. Setting up at a recorded temp/humidity/base pressure.........and watch the shift in POI at 50 yards or 100 yards as the temp rises to 10 degrees hotter.

I'd expect to see a 1 inch rise at 100 yards, a half inch rise at 50 yards, and a 1/4 inch rise at 25 yards for a 10 degC rise in temp, depending on (crucially) what temperature you set your zero. Some feedback would be good if anyone can remember to jot down those readings if they plan on spending a nice day out in the fine weather shooting for relaxation and enjoyment

Back to you......

kind regards

GS I wonder if you could copy the reports of the UK shooters for me so that I can assess how closely they followed my protocol in comparing the "bullet" types with the diabolo pellets in respect of wind deflections. ... Importantly I would like to know that they paid close attention to the necessity of the wind being at 9:00 or at 3:00 O'clock for this study. ... The incline of the PsOI can be quite affected by angled head or tail winds as in 10:30, 2:30, 4:30 and 7:30 O'clock angles.

The bullet type in my tsets follow the same pattern as is common understanding for rimfire bullets in both hemispheres. My consistent results with the diabolos are at odds with that wisdom. That is what leads me to suspect different dynamics at play for diabolos.

Thank you for the information on the Falcon scope. I shall digest that along with your information re- temp change and trajectory.

I see the facility that that scope would offer the FT shooter and, as you suggest, it could well double for most airgun hunters, shooting rifles with trajectories like mine, out to somewhat long ranges. A discrimination of 3 yards +/- at 100 yards represents a +/- one inch drop. ie., from 97 to 100 yards and from 100 yd to 103 yd I have a 1 inch margin of error to factor into the system's group size. So if the scope can discriminate to that degree then it should suffice within that frame.

In respect of temp change at my altitude; I see an approx one MOA POI change at 100 yards from around 10 C in the morning to around 20 C later in the day ( with the same 100 yard sight setting ).

I have recently done a repeat 300 yard group shoot to open a further window into real life field information on pellet stability - judged from POI attitude; penetration as a reflection of conserved momentum; and grouping ability, also dependent upon pellet stability of course.

I shall post the result shortly. I'm not sure whether you personally find the extreme range stuff interesting but there are plenty of misconceptions and generalizations projected on the forums in relation to what happens to pellets beyond fifty or sixty yards.

Thank you again for following up on the above post. ...
We are all feeling for the many New Zealanders, and some of our own, who are suffering the outcome of the mine disaster. Along with the property losses from the earthquakes it has not been a great year for you folk .... Kind regards, Harry.

Harry and all,
I would have to reflect your concern back in your direction with the floods and tropical cyclone you have experienced. We all have crosses to bear at one time or another.

I do find the testing and research you are doing very interesting indeed. While I myself am still restricting myself to more mundane ranges, I do see the particular applicability to my own competition interests. Yours is a dedication to the unknown, or to questioning the "known/assumed". We are all the richer for it, so thanks very much.
DA
Your comment regarding the POI shift you observed is in line with that I believe to hold true. It is relevant around 15.9 degC up to 30 degC, but down under the 7-9 degrees C, it doubles where relative humidity ceases to have an effect and density is proportionally greater in that type of weather anyway (fog/mist/cold mornings). What I mean is that if you set your zero at 10 deg C, a drop of 10 deg will be approx 2 MOA not 1 MOA. Above 9 deg, the 1 MOA POI rise for 10 degrees temp rise seems to hold true until you reach above 40 degrees C. Atmospheric air density is a gradient, low alt to high alt, so when DA is low it is going to effect a greater resistance than a higher DA.

I relate that back to Density Altitude, where at 4500 ft above sea level, a 20 degree rise in temp from 20 to 40 degrees resulted in 3 MOA shift on the third day of the competition. It was different each day during competition in SA, 1 MOA day 1, 2 MOA day 2, 3 MOA day 3, observed by many on a cursory basis but mostly unexplained and not understood, being blamed on rifle actions and scopes shifting/expanding etc etc. I certainly got caught out on day two predicting the same conditions as the first day and getting it horribly wrong. Hence I started to question common assumptions and believe my own eyes instead.

Wind Deflection
I'll see if I can find those comments again from the UK shooters. I gather from general discussion that it must only be a 3/9 O'clock wind to induce the rise or drop in POI. Presuming that full value wind induces it but half value wind does not.........that is also my understanding, and I think that was part of the discussion. It was also commented upon that .177 calibre seems to be somewhat impervious to this phenomenon. I personally have seen full value winds push my small calibre pellets 5 inches sideways without deflection consistently. The proviso I would insert at this point is that I have seen some very confusing results, where wind shear and turbulence around tree trunks have produced counter intuitive results for the POI. I've had pellets 'sucked' in towards tree trunks n the lee side, and pellets taken both up and down in the lee of a concrete range wall. All common sense in retrospect. I find shooting in the open field environment to be the most predictable......happily that is our most common condition with so many farms requiring pest control

Falcon Scope
Harry I do not think you will get a yard or so definition out past 100 yards, and Sorry if I implied that level of range-finding accuracy. It would give you at best 5 yards give or take at that range. Still within the 55 yards for FT shooting it will give you a specific yard with accuracy in full light....

I have always wanted to settle to some solitary BR groups at 100 yards, but there is always something else demanding my attention. I feel my rifle, myself and the excellent JSB pellets duly sorted and prepared would acquit themselves quite well given the chance.

I'll just leave you with an photo I took a Month or so ago while testing out the Falcon scope, showing why .177 at 12 ft/lbs is so frustrating to do any precision work with. No wonder the UK fellows are always so sceptical of what others say....as even a slight breath can push a supremely accurate combination off the mark by a large margin.
It is why a) I have not undertaken serious long range shooting as yet or bumped up the energy on the Steyr, b) I am always holding the x hairs every other place than actually on a bullzeye!

55 yards, .177 cal JSB Exact 8.44 gr, 793 fps, Steyr LG110 FT, wind R-L <3mph


Kind regards
Adam

Thank you for getting back to me Adam. I hope to do more work on the deflection study. However, the difference between the responses of the diabolo and the "bullet' were very marked in that study.

Yes we have had our turn with mother nature and again there are many unfortunate victims in places one would never have anticipated (flooding).
Best regards,
Harry.

And yet again, Christchurch has been hit by another big earthquake, this time involving significant loss of life and devastation of almost an entire major NZ city.

The people of Christchurch will greatly appreciate the help your Federal Government have sent in the way of Urban search and rescue personnel and equipment. So a thankyou from this side of the ditch.

One of our NZ forum members received a brand new Weirauch 98 this morning, and stated he felt guilty with what occurred the night before it arriving, and unable to enjoy his new purchase that had been 2 Months in transit. Bittersweet.

Reminds one to enjoy the "little things" while one can.......

kind regards
GS

A sad trial for all Christchurch people,not once but twice,a cruel act of nature for sure.
Our Hearts and Prayers go to all the Kiwis affected by this horrific event.

RayG wrote:A sad trial for all Christchurch people,not once but twice,a cruel act of nature for sure.
Our Hearts and Prayers go to all the Kiwis affected by this horrific event.

Well said Ray.........