Author Topic: Can someone explain how heavier pellets "buck the wind" better? (Read 1484 times)

Harpoon1 · « **on:** July 13, 2018, 01:09:59 PM »

I see this repeated over and over in the forums. "The little .177 really get blown around" or "the .22 really punches through the wind better", etc, etc,.......... But anyone spending more than a couple of minutes with any ballistic app or software will find that hard to swallow and contradictory to the known data.

I've read you "Wind and Drift" thread, and it was very educational, helpful and something I was completely ignorant of, it still leaves me wondering!

So, in broad general terms it would seem, the faster the projectile, along with factoring in it's BC, the less time the projectile is effected by the wind, i.e. the less deflection?

So what gives, what am I missing?

Can someone educate me?

TIA

Alan · « **Reply #1 on:** July 13, 2018, 02:33:24 PM »

Bob will answer your question. In the mean time, you might read this: http://airgunguild.com/ask-bob/what-is-the-ballistics-coefficient/

rsterne · « **Reply #2 on:** July 13, 2018, 03:46:51 PM »

Harpoon1, I just typed a long post and lost it....

…. In the meantime, I suggest you wade through the link Alan gave, perhaps that will answer most of your questions.... If not, post your questions and I'll try again....

Bob

Harpoon1 · « **Reply #3 on:** July 13, 2018, 05:29:25 PM »

Thanks for the link but Im not finding the answer in there.

Lets try it this way.

All things being equal, like velocity and BC/SD, the pervasive wisdom/implication on multiple forums is, the heavier pellet will experience less wind deflection. I say BS! Strelok confirms my belief. Samething with Chairgun, give various weighted pellets the same velocity, same BC, you get the same wind deflection!

Velocity and BC (i.e. time spent being exposed to the xwind) are what matter, not the projectiles weight. So why do people keep insisting
the heavier pellets buck the wind better?

Gerard · « **Reply #4 on:** July 13, 2018, 10:26:22 PM »

Perhaps I'm off base to suggest this, but... my copy of Chairgun Pro isn't giving the same BC for equivalent pellets in .177" and .22". For example the JSB Exact, a very commonly used pellet, shows a BC of 0.0210 in .177" and a BC of 0.0310" in .22". Those aren't the same numbers. So how is it that you're calling them equivalent between calibres? Checking a few other pellet models I find similarly differing ballistic coefficients. A relatively poor choice for longer ranges for example, the RWS Hobby wadcutter, is still different between them, showing 0.0120 for .22" and 0.0110 for .177", closer. They're almost equally bad at cutting through the air. So how is it you're saying things like 'all things being equal like BC and velocity...' when these things really can't all be equal between different calibres?

Besides this basic apparent error in generalisation, there's the plain fact that at longer ranges, shooters experience more serious problems with cross winds in the smaller calibres, a problem largely solved by going to larger, more efficient pellets. Look to the experts of really long range pellet shooting such as Matt Dubber or Ted Bier, or pretty much ALL the shooters who do well at Extreme Benchrest which is typically a very windy competition to shoot at. They're almost all using .25" or larger now, with I think a majority actually going to .30" to buck the wind. Are you saying they're mistaken? That they could score just as well with .177" Seems that guys who put 100,000+ pellets downrange per year in pest control, practice and competition shooting would be better positioned to know that's bunk.

Alan · « **Reply #5 on:** July 14, 2018, 04:23:46 AM »

There is another factor too. Pellets are both spin and drag stabilized, and BC aside, the actual shape of the pellets has some effect on drift. For example, most RWS pellets have grooves cur into the skirt. I've always wondered if this was good or bad with respect to drift?

Motorhead · « **Reply #6 on:** July 14, 2018, 08:38:45 AM »

I've always looked at it in a way most seldom consider ... sort of a Newtonian thing.

If you think about wind side striking an object and the energy of the wind attempting to move said object in the direction the wind is blowing & actually being able to do so ... the lighter an object is the more energy it will absorb from the side wind, where as a heavier object will be less effected. same thing can see seen with a light car being blown around while traveling down the road at 60 mph where a heavier car at the same speed is effected less. It boils down to the ratio of weight to energy absorption from the side wind over the time from muzzle to target .

So take 2 pellets traveling at the same speed but vastly different weights .. ( both with close BC values ) The lighter pellet will deflect from its flight path more so than a heavy one.

This is not the same thing happening in terms of caliber where a smaller caliber has less frontal area than a larger calber ... thats a frontal area drag thing as the projectile displaces the air it is moving threw.

Hope this make some sense.
Scott

Harpoon1 · « **Reply #7 on:** July 14, 2018, 08:49:18 AM »

Quote from: Gerard on July 13, 2018, 10:26:22 PM

Perhaps I'm off base to suggest this, but... my copy of Chairgun Pro isn't giving the same BC for equivalent pellets in .177" and .22". For example the JSB Exact, a very commonly used pellet, shows a BC of 0.0210 in .177" and a BC of 0.0310" in .22". Those aren't the same numbers. So how is it that you're calling them equivalent between calibres? Checking a few other pellet models I find similarly differing ballistic coefficients. A relatively poor choice for longer ranges for example, the RWS Hobby wadcutter, is still different between them, showing 0.0120 for .22" and 0.0110 for .177", closer. They're almost equally bad at cutting through the air. So how is it you're saying things like 'all things being equal like BC and velocity...' when these things really can't all be equal between different calibres?

Besides this basic apparent error in generalisation, there's the plain fact that at longer ranges, shooters experience more serious problems with cross winds in the smaller calibres, a problem largely solved by going to larger, more efficient pellets. Look to the experts of really long range pellet shooting such as Matt Dubber or Ted Bier, or pretty much ALL the shooters who do well at Extreme Benchrest which is typically a very windy competition to shoot at. They're almost all using .25" or larger now, with I think a majority actually going to .30" to buck the wind. Are you saying they're mistaken? That they could score just as well with .177" Seems that guys who put 100,000+ pellets downrange per year in pest control, practice and competition shooting would be better positioned to know that's bunk.

Giving them the same BC was to compare "apples to apples", a supposely theoretical comparison, not a literal example. However, while the two pellets you chose may have that large disparity, there are other .177 pellets with higher BC's than some .22 pellets of comparable weights. So clearly, choice matters.

The pervasive belief is, "heavier pellets buck the wind better", not "a higher BC bucks the wind better". There is a difference with a distinction.

And yes pf course, in broad general terms, larger pellets have better BC's, and that is why I beleive they are used for longer ranges, not because of their additional weight.

Again, this a mental exercise to try and isolate the real reason why some pellets experience less deflection. Anyone can check this with any ballistic app/software. If you give both pellets the same BC and same velocity, the wind defelction is identical, regardless of the weight difference. So, how do you reconcile that? Are you suggesting all the Ballistic software is in error?

rsterne · « **Reply #8 on:** July 14, 2018, 08:54:54 AM »

Sorry for the brief answer yesterday, I typed a long post and it vapourized, then company showed up.... I'll try and get this done before family wakes up this morning....

Weight is very important in it's contribution to BC, but only because that it increases the Sectional Density of the pellet.... The SD is the "weight per unit area", so a 14 gr. pellet in .177 has a higher SD than in .22, and a 25 gr. in .22 cal. has a higher SD than in .25 etc.etc…. The other governing factor in the BC is the Form Factor, which is an indication of the "slipperiness" of a pellet.... The three are interrelated by the formula....

BC = SD / FF

and if you know any two, you can calculate the other one.... This is complicated because the FF is different if you use a different drag model (eg. G1 or GA) you get a different BC and FF, but let's not get sidetracked and assume we are using the GA model, which is the best we have at the moment for diabolo pellets....

When I joined the Hard Air Magazine "Team" as Technical Editor, I suggested that they add two more columns to the table of Ballistics Coefficients for the SD and FF, and they have done that.... As far as I know there is no other table for pellets that shows all three numbers, and not only that, but by clicking on the top of each column, you can sort the data by the values in that column....

https://hardairmagazine.com/ballistic-coefficients/

For instance, if you sort by SD, within each caliber you will find that the pellets are then arranged by weight.... If you sort by FF, you will find that the round nosed pellets rise to the top (with bullet shapes above them, if any) while wadcutters end up at the bottom of the list.... This makes sense, because wadcutter have more drag.... Unfortunately, all the pellets are not tested at the same velocity (because they are tested in the same gun, only changing the barrel between calibers)…. Since the BC varies with velocity (and so does the FF), you can't make 100% accurate comparisions between calibers, but the imformation is still very valuable and enlightening....

Bottom line is that for a given shape of pellet (eg. the JSB EXact Series) the BC tends to follow the SD, regardless of caliber.... It's not a perfect correlation, because the velocities tested are not all the same.... and the shape does vary because of the weight changes, so the FF isn't always the same.... but you will notice that the JSBs tend to have the best FFs, which means they are one of the lowest drag pellets around.... In fact, when I am curious about what the BC may be of a new JSB Exact, I calculate the SD and divide by a FF of 1.5 to approximate the BC.... In many cases, it is pretty dang close....

The Wind drift is dependant on the Drag Coefficient and the velocity.... It is strictly related to the "lag time", which is the difference between the flight time of your pellet and what it would have been in a vacuum.... Even if the BC was a constant over the entire range of velocities, as I explained in the thread Alan linked above, the Cd is not, it has a huge increase in the Transonic range (Mach 0.8-1.2)…. This means that even though the flight time is shorter at high velocities, the lag time is greater, and so is the wind drift.... Here is a diagram showing what happens to the wind drift at different velocities....

and here is a more detailed example for a typical RN pellet at only 50 yds....

I hope this helps clarify things for you.... Yes, weight is important, but so is the shape and the velocity, in determining the wind drift.... All three factors interrelate, and not in a way you can easily calculate, because the drag (Cd) curve is different for each pellet, and basically none of them precisely match the GA model which programs like ChairGun use to calculate the trajectory and drift.... Still, at the present time, it is the best tool we have, and you can make two generalizations....

At a given velocity, a higher BC pellet will have less wind drift....

For a given BC and range, there will be an optimum MV where the drift will be at a minimum....

Bob

Harpoon1 · « **Reply #9 on:** July 14, 2018, 08:57:12 AM »

Quote

So take 2 pellets traveling at the same speed but vastly different weights .. ( both with close BC values ) The lighter pellet will deflect from its flight path more so than a heavy one.

Scott

Respectfully, at least according to Chairgun and Strelok that is simply not true.

You can double check it yourself dude, its the velocity and BC that matters, weight is third or fourth order. Shoot an 8 grn .177 vs a 16 grn .22 at the same speed, with the same BC and you get identical wind deflection. Dont take my word for it, check it out for yourself.

Motorhead · « **Reply #10 on:** July 14, 2018, 09:08:32 AM »

I live in the real world and SHOOT COMPETITIVELY ..... my experience is hands on real world.
While math and data for most rule the day, for me I take results at face value in spite sometimes to what the data may say.

I'm old school learning from doing ... so right or wrong in eyes of others it really don't sway me much.

This is the internet and we all are just sharing life experience & belief in what were doing.
Ones success can be weighted / connected somewhat to what you think you know ... I'm doing just fine

rsterne · « **Reply #11 on:** July 14, 2018, 09:14:06 AM »

Respectfully, Scott was referring to two pellets in the same caliber, and of approximately the same shape, in which case his statement is correct.... The heavier pellet would have a higher SD and a similar FF, so therefore a higher BC and less wind drift when starting at the same velocity....

However, Scott, since a pellet is constantly loosing energy, not gaining it.... a more accurate statement might be that is boils down to the energy LOSS to the sidewind.... A pellet with a higher BC will lose less energy to the side wind, and in doing so the "lag time" will be less, so it will have less wind drift.... Harder to understand, but more technically correct, IMO....

Bob

rsterne · « **Reply #12 on:** July 14, 2018, 09:17:18 AM »

Alan, sorry, I missed your post about the "Magnus effect", which is more pronounced on ribbed pellet than smooth.... In a crosswind that causes the pellets to RISE or FALL, depending on the direction of the twist relative to the crosswind, it doesn't affect the sideways drift.... The same effect causes backspin on a dimpled golf ball to have a higher trajectory....

Bob

Harpoon1 · « **Reply #13 on:** July 14, 2018, 09:18:25 AM »

Quote from: Motorhead on July 14, 2018, 09:08:32 AM

I live in the real world and SHOOT COMPETITIVELY ..... my experience is hands on real world.
While math and data for most rule the day, for me I take results at face value in spite sometimes to what the data may say.

I'm old school learning from doing ... so right or wrong in eyes of others it really don't sway me much.

This is the internet and we all are just sharing life experience & belief in what were doing.
Ones success can be weighted / connected somewhat to what you think you know ... I'm doing just fine

Scott

Im not here to argue with you, to the contrary, Im here trying to get answers. Its not personal, at least for me it isn't. Frankly, you've foregotten more about airguns then I'll ever know. Having said that, I still cant reconcile why the ballistic apps come to a different conclusion.

Harpoon1 · « **Reply #14 on:** July 14, 2018, 09:23:36 AM »

Quote from: rsterne on July 14, 2018, 09:14:06 AM

Respectfully, Scott was referring to two pellets in the same caliber, and of approximately the same shape, in which case his statement is correct.... The heavier pellet would have a higher SD and a similar FF, so therefore a higher BC and less wind drift when starting at the same velocity....

However, Scott, since a pellet is constantly loosing energy, not gaining it.... a more accurate statement might be that is boils down to the energy LOSS to the sidewind.... A pellet with a higher BC will lose less energy to the side wind, and in doing so the "lag time" will be less, so it will have less wind drift.... Harder to understand, but more technically correct, IMO....

Bob

Bob,

I agree, completely and well said.

Edited: and your right, it does look like he was comparing pellets of the same caliber. In which case I agree.I glossed over the last sentence or twon in his post. My apologies.

However, the more common belief is, the .22 bucks the wind better than the .177 because its heavier!