Understanding Wind

Ah, so you do. My apologies for asking.
I guess I read but didn't properly digest it before looking though other posts mentioning tables :-(

 

Correct me if I'm wrong, the diagrams make it look like there's more drag affecting the pellet, does this mean that my pellets will also drop more than on a still day?

 

The total air velocity will be made up from the combination of the pellet forward speed and the wind velocity which means that, in a cross wind, it will be greater than from the forward speed alone. However, in any wind you are likely to be trying to shoot in, the pellet forward speed will be many times larger than the wind speed. This means that, although strictly speaking there is an increase in drag, you are unlikely to notice any difference at airgun ranges and it will be a very minor effect compared to the other errors.

 

This appears essentially the same thing as the apparent wind we see on a sailing boat or aeroplane, including the same tendency for that boat or aeroplane (cf pellet) to try to turn towards the true wind. I think all of them respond to the same issue of the wind impinging on the directionally stabilising element of the projectile/vessel, e.g., the skirt of the pellet, the fin of the aeroplane, the mainsail of the sailing boat. That downwind drift seems to me pretty much equivalent to "leeway". Sailing boats don't tend to do 800fps, so the effects are much more pronounced

https://en.wikipedia.org/wiki/Apparent_wind

 

To avoid it.. I avoid our lasses cooking..

 

Does this mean that it in not possible to make an informed choice of pellet to best resist wind drift without knowing the BC of each pellet?

 

By knowing the BC and the muzzle velocity of any pellet from your gun it will help you to select a number of pellet designs which should minimise your down wind drift. It will not tell you anything about other aspects such as dispersion from your gun (group size) or even the vertical cross wind effect which can be significant at longer ranges.

 

How does one find out the BC of a particular pellet?

 

The easiest way is to use the values from the Chairgun lists since you know they are all related to the GA drag law. Some manufacturers quote numbers but you never know what drag law they are based on and therefore cannot be used for comparison.
Some will say you need to obtain it for pellets from your own gun as it will vary from gun to gun. There is some slight variation it is true but it will not be significant at airgun ranges unless there is something drastically wrong with your gun pellet combination. The vast part of the quoted measured variations is down to poor experimental technique, bad instrumentation practices and a lack of taking the atmospheric conditions into consideration. You can obtain it for your own gun but you will need at least two calibrated chronographs and wind and meteorological measuring equipment or information on the atmospheric wind, temperature and pressure where and when you are shooting. There are also specific experimental techniques to be followed if you are trying to compare two or more pellets.

 

Chairgun has a very good list, but I found this interesting: "Secrets of the three shot calibration"

 

box of tissues for Twoplusfour lol

 

It's alright, I'll just wipe it on the curtains

 

old habits die hard hey!

 

seems some of us may share more than one shooting hobby lol

 

DID YOU NOW YOU CAN GET TABLETS FOR IT

 

And oldies

 

Well back to the mundane this afternoon armed with my two recoiless fwb 300's i selected 20 yds as a reasonable distance. When i was new to these fantastic recoiless rifles i was hugely surprised what they were capable of with opens and the groups they could produce. It was scope accuracy at 20/25 yards with groups under half inch being easlly attainable. Then i got into the open sights comp run by Mikey and put the 300's on the back burner and became very much in love with my brand new 77 equiped with a diopter and a globe front sight and inserts. At the begining of this thread i started by comparing my 300's and my HW77. I have just shot 3 cards 4 bulls on each card and here they are. The results surprised me. They were all shot one after the other in exactly the same wind conditions. Express for the 300's and qys for the 77. The clear winner was the HW77. I dont know whether to be elated with my 77 or disapointed in the 300's.

 

Jumping into the middle, I would presume there are calculatable relationships where one aspect of a pellet might overwhelm the other factors in describing ballistic flight path, several of which may already be factored into the ballistic coefficients. Heavy pellets may tip the BC substantially - getting back to the importance of the BC in the equation, and may still give the empirical result of "heavy pellets shuck the wind better" found in experience. Also, is comparing rockets (powered flight, I presume) to projectiles (unpowered flight, just a big shove at the beginning) might not be fair - would not a better comparison be for artillery projectiles? Of course, I have NO idea of what that impact would be (other than a splat at the end!) of the effect on a pellet. It is interesting to look at the physics of flight dynamics, and thanks for the excellent dissertation.

 

Heavy pellets do not always work better in the wind, it is more a matter of design rather than weight and anything else which can affect the all important lag time. As for rockets they are no different to any other projectiles large or small in how they react to the wind. I could have used rocket assisted shells as the example for the same results or base burn assisted shells which show reduced wind drift while the motor is burning. The only difference for rockets is that, assuming they are not an ABOL rocket (all burnt on launch), the acceleration phase lasts a little longer than it does for a gun launched projectile. Because of this the effects of the net drag on the wind drift can be seen and rockets can clearly be seen to drift upwind during the acceleration phase when the net drag is negative. When the motor has burnt out then the normal drag forces take over and the rocket begins to behave like and other unpowered projectile.

 

Wow had to read this 4 times and a friend explaining it it's a lot better than mine ,left a bit ,right a bit, explanation