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Pellet speeds vs lateral pellet drift

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1 click = 1/10th MIL, and 1/10th MIL@ 30 yards = 1mm....not 5mm, where do you get your 5 mm figure from if I may ask?



Two other phenonomans cause this effect, and the physics ALWAYS applies, its just a matter of how MUCH it applies. The Coriolis effect...and the Magnus effect. They play a role even at 1 yard, its just a matter if its observable to the human eye...lol...



Scope CANT and Bent barrels can have the same effect. OP tested on 2 rifles, either both his barrels are bent the same way the same amount OR his scopes are canted equally...



Hawke charigun pro (designed FOR airguns) implemented Gyro Coefficients into their ballistic program for a reason, Sterlok has spin calculations as well...they don't have bent barrel modifiers...so take what you will with the information I've shared.
 
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1 click = 1/10th MIL, and 1/10th MIL@ 30 yards = 1mm....not 5mm, where do you get your 5 mm figure from if I may ask?

Click to expand...

I re-did the whole thing properly last night when I had the time. Given some variability due to shooting and pellet groups, it is really much closer to slightly less than 1.5mm. I noticed on my scope turrets, the variation is 1 click or so left when i shot at 650fps instead of my zero at 900fps - my 30 yard basement range is perfectly windless with perfect conditions, for me to be able to tell a 0.1 or 0.2 mil variation with consistency.

Not sure about me having bent barrels or canted scope, because with StrelokPro and Chairgun, I am spot on from 25 yards out to 150 yards for both FX Impact and W.A.R Flex 357...
 
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Barrels Whip, they do not oscillate or shake side to side nearly to the degree they do up/down, I encourage you to research this yourself. Additionally, air rifles operating at very low pressures AND energy outputs experience MUCH less 'barrel whip' and more so vibration... If you think 2000 psi rushing down our air guns barrel cause enough harmonics to alter a projectiles trajectory up to 1.5mm at 30 yards, I don't know what else to say...I'm speechless to think people believe this is even a possibility with air guns. 



Its more likely for the pellet to deflect due to physics outside the barrel in its 30 yards it travels to target...than barrel deflection of such degree at such low pressures....again, hawke chair gun an application designed to calculate the external ballistics of PELLETS implements spin drift into its calculations, why are people refusing to accept it is BEYOND me.



Also its FAR more likely to be scope CANT issues than barrel harmonics, as I've tried to explain harmonics is more a function of up/down...bullet flies FORWARDS, pressure is released 'FORWARD' inside the barrel, in one plane/direction...which makes the front of a rifle jump UP/BACK as well as the barrel 'whip' effect. 



-Matt
 
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1 click = 1/10th MIL, and 1/10th MIL@ 30 yards = 1mm....not 5mm, where do you get your 5 mm figure from if I may ask?
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From the original post maybe?

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In his Original Post he stated 'about', and later confirmed it to be 1 click or roughly 1mm...whats the point of posting in a thread if you only read the original post and no follow ups...sigh
 
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Everyone has an opinion, Matt, and you might be correct. I don't believe so, but you could be. In my opinion there is no way to know that all barrel movement is in the vertical plane. And yes, cant could be an issue as well but is controllable by the shooter. Barrel harmonics is not.

My question would be does anyone ever see POI movement to both left AND right related to velocity change? If so, then it seems it could not be spin drift.
 
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The original 5mm over-estimation is how it looked to me from bench when viewed through my scope at 27x magnification from 30 yards. When i re-did the experiment proper and measured with calipers instead of estimating thru scope at 27x magnification, it was closer to 1.5mm. Given that the pellet groupings were pellet on pellet, any unexpected shift seemed huge...

Now, I wish i can do the experiment using my son's crosman pumpmaster that has no rifling, but it is just not accurate enough to test with. Now, people might ask, how sure are you that you can tell a 1/10th of a Mil variation at 30 yards? 

In my basement with perfection conditions, i assure you I can tell up and more than half of a 1/10th Mil(yes, that is 1/20th of a Mil) variation with the FX Impact X and W.A.R Flex 357. Just over the weekend, my zero in the FX Impact resulted in it being on the left of the target pencil line drawn, but one click right resulted in it going to the right of the target pencil line, but just NOT center, i needed 1/20th of a Mil click! Given the OCD, I re-mounted the scope several times, adjusting the tightness of the screws, etc... till I got it to zero exactly on the target line.

Long story short, I can tell pellet shifts within less than 1/10th of a Mil in perfectly windless conditions in my basement. Just fyi, my scopes are no slouches either, I have a Athlon Ares and Athlon Cronus on these rifles.
 
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Everyone has an opinion, Matt, and you might be correct. I don't believe so, but you could be. In my opinion there is no way to know that all barrel movement is in the vertical plane. And yes, cant could be an issue as well but is controllable by the shooter. Barrel harmonics is not.

My question would be does anyone ever see POI movement to both left AND right related to velocity change? If so, then it seems it could not be spin drift.
Click to expand...



I am not expressing opinion. I am sharing a wealth of knowledge that is available for you OR ANYONE to research themselves, including physics such as gyroscopic procession, magnus effect, Coriolis effect (effects pellets yes, especially due to time of flight @ range...), barrel deflection, scope cant. All possibilities...but the one that is inevitably contributing to his horizontal shift has already been confirmed through external ballistic apps both by OP and myself.



Science/physics is not opinion based, its fact based.



Barrel whip and movement is PRIMARILY in the one plane yes, and vibration / frequency is felt in all dimensions of space...but the one most effected is up/down...I am not in any way dismissing barrel harmonics can and will have a play in group size and changes in point of impact, that is well known and established...just as much as the physics I've mentioned that apply externally to our pellets. However, as stated the main change in OP's point of impact has been resolved by OP with sterlok pro...I am sure if that changes he will update. I am always ready and willing to be wrong :)
 
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There is no doubt in my mind that there is spin drift, even for us pellet shooters. For those that doubt the science and physics, check out StrelokPro. Toggle between "Enable Spin drift" vs not enabling it. For my FX Impact X data, this results in windage of 3 clicks(0.3 mils) left at 140 yards, instead of the default zero windage if spin-drift is not taken into account - this is significant on a perfect condition windless day.

This actually explains a lot of my longer distance aim points. In short, if you are shooting at the same muzzle speed and shoot less than 100 yards, spin drifts matters little to you. But if you are shooting longer distances and have a consistently accurate rifle, it matters. Conversely, it also matters if you shoot various pellet muzzle speeds(in my case, 900fps down to 650fps) and want to use a single windage zero based on a certain speed - if the muzzle speed variation is huge, you will need to consider spin drift, although it is small, 1/10th of a mil or 2 at most.


 
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+1 Frank, concurred. Its VERY little variance, barely noticeable but its there, the further out you shoot the more it becomes apparent.



For giggles, to eradicate the barrel harmonics theory. Its undeniable the biggest induced change of POI is with the condition of barrel whip, where the pellet exits the barrel when its up high or down low based on how much it whips and pellet speed. 



If the above were OP's issue, he would have more VERTICAL POI drift than HORIZONTAL, without question...and his sterlok pro calculations would be terribly off vertically. If op's sterlok plus calculations are pretty spot on vertically, then he is not experiencing dramatic barrel whip or harmonics that greatly effect POI...
 
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ackuric,

I agree completely. I always wondered why my shots further than 125 yards were always landing slightly right of the target - based on 30 yard zero and using elevation turrets only. I just usually blame it on my shooting technique, or that I just pulled the shot, or just wind. But i noticed that at my 140 yard target, the right side of the target had more misses(a much bigger dirt hole caused by the misses). After enabling spin drift on StrekokPro, it is now asking me for 3 clicks left to account for spin-drift. and viola, what do you know, accounts for my previous misses exactly! Missed dirt hole + 3 left clicks equals center of target - I love it!
 
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Frank,

I am OCD like you, I am an engineer by profession, I really like airguns and more than anything shooting under an inch at 100 yards. Most people don't take me seriously but I can't do anything about that.

I have 100 yards of indoor range, with and without wind, many FX guns, many scopes, doppler, digital levels, range finders, thermometers, barometers, plumb lines, scope mounts that cost more than scopes, holding scopes that cost more than guns, and I shoot just about every day. I can’t shoot for much but I enjoy the heck out of every last bit of it!

I have only been at this hobby for a few years so I am by no means an expert at anything airgun related, but if I zero my guns at the top of the pellets trajectory for a given velocity above 850 fps (between 30 and 43 yards), then at 100 yards my pellets will hit left of the center line of aim. Depending on the gun the bias is more or less extreme.

I can index my barrel on some guns, and make it shoot more left, right, up or down, I like to try and get the most up bias. It still shoots a bit left downrange.

I have shot more guns than I should because I know a friend of a friend kind of thing. Some guns shoot really poorly so it’s hard to tell much from the spread pattern, but some guns that are let’s say hand-picked by some gentleman in Sweden, they shoot amazingly well! They also shoot a bit left at range for me...

Long story short, if I enable spin drift and left hand twist in strelok the predicted POI matches my poor equipment, technique and shooting in perfect conditions. I think the perfect conditions make things like this really stand out, also looking for mm accuracy at range (100yards) exposes all the factors that affect shooting. Science is quite clear about this.

My cranky neighbour used to complain that I used to shoot on my property every day, and while legally allowed to, I was being a nuisance, some people! I joined an indoor range, arranged a daily rate card, paid in advance and I never looked back, I also started to see more theoretical science in practice due to the perfect conditions.
 
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