Round ball wind drift?

[LH]

Playing around with a couple of wind drift calculators I came across something puzzling to me.  I used ballistic coeficents for different sized balls from the Lyman black powder book.  Starting at 500fps muzzle velocity, the wind drift decreases as velocity increases up to 1000fps at which point it begins to increase as velocity goes up until you get to 1800fps and then it reverses again and begins to decrease.  Is this right?  I don't understand all I think I know about round ball ballistics,  but this seems mighty odd to me.  I did find one reference to .22 rimfire ammo in an army ballistics file that stated .22lr ammo was effected less by wind at velocities around 1000fps than at higher velocities of about 1300fps.  I've heard and I'm sure most of yall have too, that "you cant hit nothing with a .32 caliber because any little wind will blow it slam off the target".  Well,  according to these calculators I've been playing with,  the difference between a .32 ball and a .54 ball at 100yds in a 5mph wind is about 1.5".  At a mv of 1500fps.  It shows 5.9" for the .54 and 7.4" for  the .32.   I dare say that's not enough for an offhand shooter with open iron sights to ever notice.  And unless you've got a rifle that will print something like 1" groups off the bench,  even a bench shooter would have a hard time proving any difference.  Is this info right?  Based on what little experimentation I've done with a .40 cal and a .54 cal,  it seems it might be correct.

[bob in the woods]

On a windless day, off the bench , many if not most of my rifles will stay in the 10 ring at 100 yards. That is with a peep sight. The error is in sighting, not the rifle.  The variables are simply less significant with a larger bore rifle.
ie a couple grains difference in ball weight, or powder charger etc etc.  We had a competitor at our club that used a .36 cal for all his shooting. He was usually in the top 5 at any match. Having said that, most of the target shooters I know who shoot at 100 yds and further , use .54's

[JPK]

As a projectile moves thrue the speed of sound it creates a shock wave that puts a drag on it. Below the speed of sound the wave isn't there and well past the speed of sound the wave is behind the projectile. Time of flight allows the slow bullet to drift longer and a larger projectile (shape being the same) has a better ballistic coefficient.

[Don Adams]

Have you used this link before?  http://www.ctmuzzleloaders.com/ctml_experiments/rbballistics/web_apps/rb_ballistics.html

[Molly]

http://www.ctmuzzleloaders.com/ctml_experiments/rbballistics/rbballistics.html

Good stuff

[Don Adams]

I use this along with the roundball ballistic chart since I don't have a chronographhttp://www.goexpowder.com/images/LoadCharts/RB-Rifle-Musket.pdf

[WadePatton]

Playing around with a couple of wind drift calculators I came across something puzzling to me.  I used ballistic coeficents for different sized balls from the Lyman black powder book.  Starting at 500fps muzzle velocity, the wind drift decreases as velocity increases up to 1000fps at which point it begins to increase as velocity goes up until you get to 1800fps and then it reverses again and begins to decrease.  Is this right?  I don't understand all I think I know about round ball ballistics,  but this seems mighty odd to me.  I did find one reference to .22 rimfire ammo in an army ballistics file that stated .22lr ammo was effected less by wind at velocities around 1000fps than at higher velocities of about 1300fps.  I've heard and I'm sure most of yall have too, that "you cant hit nothing with a .32 caliber because any little wind will blow it slam off the target".  Well,  according to these calculators I've been playing with,  the difference between a .32 ball and a .54 ball at 100yds in a 5mph wind is about 1.5".  At a mv of 1500fps.  It shows 5.9" for the .54 and 7.4" for  the .32.   I dare say that's not enough for an offhand shooter with open iron sights to ever notice.  And unless you've got a rifle that will print something like 1" groups off the bench,  even a bench shooter would have a hard time proving any difference.  Is this info right?  Based on what little experimentation I've done with a .40 cal and a .54 cal,  it seems it might be correct.

99% of the ballistics engineering data/programs/charts/apps etc. you find are going to be for pill-shaped objects and NOT directly applicable to spherical projectiles.  

I haven't examined those posted above-they may be perfect, but most available aren't-they aren't even close. Trust me the subject has been discussed here and other places over and again.  There is a bit of "unlearning" that helps if one comes to roundball shooting from the suppository games.

Shoot and see is the absolute bestest option.  Which means first developing your most accurate load that requires no extra wiping (loading patch does all the wiping), then firing that load with a consistent point of aim and noting the vertical and horizontal dispersion at various ranges.  Correction factors are of course: humidity, temp, barometric pressure and wind speed/direction  (which is rarely consistent down the line in speed or direction and varies all day long).  This is much more accurate and fun and noisy than punching in numbers.  

[Daryl]

I use this along with the roundball ballistic chart since I don't have a chronographhttp://www.goexpowder.com/images/LoadCharts/RB-Rifle-Musket.pdf

Interesting chart, Don, however the 80gr. charge listed as max. in the .69 will usually disappoint a great deal past 50yards.  I use 3 drams, 82gr. as a plinking load only, going up to 140gr. 2f or more for serious target work. Believe me, the .69 can be a serious target-type rifle when you want it to be.  It can be a bit rough on the shoulder and a PAST shoulder protector sure helps when benching her.

[Don Adams]

Understood Daryl.  I wished they had the powder chart start for a .32 caliber - I own a .32,  a .40 and .50 caliber. 

[Daryl]

My .32 makes just over 1,740fps with 35gr. 3F GOEX, it's best load with a water based lube, .311" or .320" ball and .022" denim or .0235" ticking patch. I use the same loads with both small and the bore sized ball. If using a slippery lube, ie: oil - I have to use 40gr. 3F - however I did not chronograph that one - I suspect a bit more speed. The extra powder is needed to regain accuracy lost in going to the slippery lube.
20gr/ 3F, will put 5 shots under a dime size, at 25 yards off the bench, but will blow the groups out to 2" and over that at 50yards. More powder is needed to maintain accuracy at the longer ranges, just as with any rifle.  As well as with any rifle, the heavier charges also shoot well at close range, thus, I do not adjust powder charges for the range being fired. Tried that and oft times had the wrong charge for the target being shot. So - one charge, learn how to hold at every range - done - for me, simplicity works.

[Dan]

Gentlemen, the physics of drift are different with round balls and conical bullets, and it is a mistake to draw inference from one to the other in many respects. 

The common element in calculation or analysis of drag in the transonic velocity range is represented here, where Cd means drag coefficient and Mach number is a measure of speed relative to that of sound:



The velocity of interest in the transonic range is not so much that of the bullet or ball, but the relative velocity of the flow field around the projectile.  Projectile shape has a lot to do with that.  It takes greater acceleration of the air to get around 'short and fat' than it does 'long and sleek'.

When looking at conical bullets part of the analysis is bullet form, sectional density and the difference between measured time of flight (ToF) as compared to ToF in a vacuum.  The resultant time value gives a measure of drag over the course of the bullet's flight, but it becomes a calculation that is specific for that distance and cannot be construed to result in a linear construct for analysis.  In simple terms, the resultant cross wind vector presents as drag and that is what deflects the bullet off course.  Add to that, the mechanics of gyroscopic stability and resultant influence... it will keep your calculator busy for a spell.  With that said, drag has a primary influence upon drift/deflection on conical bullets.  The transonic velocity range is where it has the most profound effect.

Round balls are not, well, conical. They are not stabilized gyroscopically  in the classic sense due to the very slow twists used in such guns.  Even if the twist is fast enough to impart such stability there is a circumstance where the Center of Gravity and Center of Aerodynamic pressure are one and the same, ergo, there is no influence on the ball's motion due to that factor.  What you are left with in calculation of drift with round balls is time of flight.  Larger caliber balls carry a slightly higher B.C. and will slow less over a given distance.  Their deflection from wind corresponds directly to time of flight and little else.

[WadePatton]

Excellent post.

[Leatherbark]

At Friendship this past fall I was shooting the bear sillouhettes. The big 10 ft long flag up on the pole was blowing straight out to the right.  I had to hold on the bear to the left at 200 yards for a good wind drift aiming point to hit the one I needed to to the right.  Sadly most of my hits with my 45 were dings. The bears are cupped so bad from repeated hits and the stands cause the bears to lean forward.  These two mitigating circumstances allow a 45 ball to only knock over a bear if the hit is in the head.  But I digress.  Don't kno what the wind was but it was definitely over 10mph with that big flag as big as the one on Mount Suribachi as it was pointing north and I was shooting west.  At least24 inches of windage required that day at 200 yards.

Bob

[LH]

Thanks Dan,   so am I understanding correctly that there is little difference in wind drift over the same range for a .32 ball vs a .50cal.  ball when velocities are nearly the same for each?   

[Frizzen]

My 32 pistol  duplicates  22 match ammo. I shoot a 45 grain ball at 950 fps. I used to shoot a 45 cal
and I can say I am less affected at 50 yds by wind with the 32. I shot and won the 100 yd pistol match
at Friendship last year . Wind was about 5-7 mph. My first five shots were 3 tens and two 9's in a group
you can cover with your hand. I held dead on. Didn't feel the wind affected me at all.

[L. Akers]

My 32 pistol  duplicates  22 match ammo. I shoot a 45 grain ball at 950 fps. I used to shoot a 45 cal
and I can say I am less affected at 50 yds by wind with the 32.

Was your .45 truckin along at 950fps?

also a pistol shooter.

[bob in the woods]

I have seen a number of shooters go up in calibre with the idea of bucking the wind better.
Problem usually comes when they dial back the velocity because of recoil.
60 grains of powder in a .54 was a common load at our club. Some used the charge to 80 gr at the 100 yard target, but my .40 with the same 60 gr shoots rings around them.
This weekend I shot a 49/50 off hand with it. 

[Dphariss]

Playing around with a couple of wind drift calculators I came across something puzzling to me.  I used ballistic coeficents for different sized balls from the Lyman black powder book.  Starting at 500fps muzzle velocity, the wind drift decreases as velocity increases up to 1000fps at which point it begins to increase as velocity goes up until you get to 1800fps and then it reverses again and begins to decrease.  Is this right?  <snip>

Yes.
Its really bad regardless compared to long bullets. It gets worse as velocity approaches the speed of sound shock waves. Drag increases greatly from +- 1050 fps to 1200 or so.
Wind drift, as I have seen it explained, is determined by the amount of TIME the bullet loses going to the target vs being shot with no drag. Round balls are high drag, they slow quickly and produce a lot of wind drift.  Also understand that the ballistics programs are generally optimized for modern low drag/HV bullets. So the data for a RB or a BPCR slug might not be as accurate as for a modern HPBT bullet launched at 2800 fps.

Dan

[Dan]

Thanks Dan,   so am I understanding correctly that there is little difference in wind drift over the same range for a .32 ball vs a .50cal.  ball when velocities are nearly the same for each?   

Might depend on what you characterize as "nearly the same"?  Problem I see with the analogy is that without some minor hysterics you won't wind up with comparable MV with the two calibers in the field.  Play around with the calculator a little...keeping in mind the ranges you  will likely use the gun at.

http://www.ctmuzzleloaders.com/ctml_experiments/rbballistics/rbballistics.html

Time of flight is a function of initial velocity, drag and distance.  Compare apples to apples.  I suggested earlier that roundball drift is largely a function of ToF and little else.  The "little else" part of it does not mean there are no other factors at play, only that they are not terribly significant.  If you fiddle with that calculator take a look at the drift numbers when initial velocity is subsonic at the muzzle. 

[LH]

Since I posted this over two years ago I have built a .36 caliber gun and have done a lot of testing (bench and offhand) on same days/same conditions between the .36 and the .40  and some with 36, 40, and 54, and as near as I can tell,  these roundball wind drift calculators are dead on the money.  So for me,  I have decided that the old "you cant shoot light caliber guns at 100yds"  saying is meaningless for me and my  shooting.  On the very best days I can only hold about 4" or 5" centered for five shots at 100yds offhand.  Most days its more like 6" or 8", so a difference of an inch of wind drift is hardly noticeable to me when I switch from the .36 to the .40 caliber.  Wind drift in the real world is never consistent and neither is my shot placement,  so 15% more wind drift = nothing for me.  I have been shooting the .36 for six months (probably 500 shots) and find it no harder to deal with in the wind than a .40cal.  Whenever possible, all the shooters I know will wait out wind.  Bench and offhand.  Even on windy days, we'll wait for a lull and at least try to time the shots when the wind is less. 

[yulzari]

Drift with a spherical ball is a function of size and speed in relation to the wind vector. The 'fore and aft' effect of the wind vector is to either lengthen or shorten the time of flight. The horizontal vector is the drifting force.

Assuming the same density (ie how alloyed with metal other than lead with pure lead being densest) then mass is a direct relation to the size of the ball.

The drifting effect is a function of the force of the drifting wind vector and of the time over which it affects the ball i.e. time of flight to the target.

A larger ball will have a lesser ratio of surface area (over which the drift acts) to volume and mass so as the ball gets larger the wind power has to move more mass for each unit of surface area upon which the force acts. Thus a .32" ball is affected far more than a .75" ball for the same time of flight.

This last also applies to the speed of the ball in that the same ratio applies to forward motion as well as sideways drift. Thus our example .32" ball will slow far faster than our .75" ball which has more mass for it's surface area to be slowed.

Mentioned above is the transonic issue where the ball both meets increased drag as it enters the transonic zone and exits it but also becomes more unstable as the airflow and shock waves pass across it in transit. This can be minimised by ensuring the ball is slow enough to stay below the transonic zone or fast enough to be comfortably above the speed of sound and also free from this issue.

You can feed the numbers into a complicated sum.

In practical summary however, you can minimise wind drift by driving your ball faster (but see 'transonic') or using a larger ball.  Or wait for the wind to go away or die down. All in all the traditional hunter gatherer answer is to get closer and this we see in survival hunting where dinner and not bragging rights are the purpose. The real life answer is to fire at varying distances in varying winds until you know what the effect of different winds are on your gun/ball. In hunting how close you have to get before the wind drift becomes too difficult for you to compensate. The finest shots can judge the compensation and do the same for bullet drop with gravity over time of flight in combination with fine trigger control. In the field add in estimating the distance to the target which is already done for target shooters. Get all of these right and you are a World Champion. My skills would not let me be trusted with making the tea and biscuits.

[alacran]

In offhand shooting I tend to agree with Mr. Patton, "shoot and see".
A steady wind of 15 mph is preferable to a variable wind of 10 mph. The winds effect on the ball Is not as significant as the effect it has on me.

[Bill in Md]

I solved the wind drift problem many years ago. I simply chose back then to never sight in, shoot, or hunt with any weapon that casts a projectile on windy days.

[Dphariss]

I solved the wind drift problem many years ago. I simply chose back then to never sight in, shoot, or hunt with any weapon that casts a projectile on windy days.

I generally don’t hunt if its windy 15 mph or more with a RB. But it has its advantages. If hunting creek bottoms or other timber it make the environment noisier and it easier to get close. On windy days I will hunt with something else.. And the ranges are shorter.
Where I live not hunting in the wind is not an option.

[Bob Roller]

Round balls are a convenience and for close shots,very effective and some have made long shots with them but as described,a 45 caliber round ball hits with a clink instead of a clang.I think that size ball weighs about 140 grains.There was a reason that long cylindrical bullets became THE bullet for extreme distances and they DO hit with a clang instead of a clink.The ball sheds velocity fast and there is no way around it.A round ball  for a close shot on a deer will work but remember the buffalo herds were nearly hunted to extinction using long bullets that could sustain killing velocities beyond 100 yards or even 1000 in some cases.I have done a lot of shooting with both ball and bullet and the difference was as noticeable as the performance between my 1946 Plymouth and my 1937 Cadillac V12.or maybe I should use my Leonard Meadows SMR  45 and my Whitworth with the 451 Henry barrel as a comparison.
Bob Roller