Reduced velocity for decreasing wind drift

[flatsguide]

I shoot exclusively PP bullets so posting this question here. It is well known that .22LR subsonic loading has significantly less wind drift that the same bullets flying above the speed of sound and the .22 LR loads that drift the most are the highest velocity loadings. My PP loads in .45-70 is an elliptical 530gn bullet driven by 81.5 gn of 1.5 Swiss giving me a velocity of 1250 FPS. This is in the same ballpark as some of the .22LR higher velocity loads. Should I get less wind drift by reducing velocity to just under subsonic and also get an additional accuracy boost by not going into the transonic instability since I would be below the speed of sound at the muzzle?
Thanks Richard

[Don McDowell]

I think it best to find the best grouping load you can. Then learn to read the wind and mirage. I've witnessed 45 caliber bullets of the same style weight etc, being shot by different shooters out of different guns at the same match, and chances are the 45-70 doing just short of 1200 fps, will come out of the match with just as good and sometimes better score than the shooter using a long case with a scoop shovel full of powder , doing close to 1400 fps.
While it is true that the standard velocity 22 loads hold up better at 200 yards in the wind than the high velocity and super high velocity loads, the tiny speck of a bullet the 22's use, it's not a good comparison to the bullets shot in BPC competitions.
I believe in BPC it's more a matter of matching and keeping the bullet length just slightly under what the twist of the barrel should stabilize, especially as the bullet travels out and goes well below that transonic zone.

[jdfoxinc]

The longer the bullet is 'in the wind' the more effect the wind has.

[Petrol & Powder]

I think you're starting with a false premise.
Your statement, ".....It is well known that .22LR subsonic loading has significantly less wind drift that the same bullets flying above the speed of sound and the .22 LR loads that drift the most are the highest velocity loadings. ...." is not completely true.
.22LR projectiles that start out supersonic and then transition to subsonic speeds before reaching the target, often exhibit larger groups - BUT that's not necessarily a result of wind drift. The transonic loss of stability isn't absolutely tied to the effects of wind on the bullet.

Wind drift is the force of the wind pushing on the projectile in flight. The longer a crosswind has to act on the bullet, the greater the distance it will deflect the bullet's path.

The advantage of starting with a subsonic velocity is that the bullet never transitions from supersonic to subsonic because it was never supersonic to start with. The slower projectile will be in flight to the target longer than a faster projectile travelling the same distance and the wind will have MORE time to act upon the slower projectile. However, if the slower projectile is more stable in flight and the wind is constant (or the shooter is very skilled at adjusting for wind deflection) the projectile may still land where you want it to land.

So, you're not exactly wrong but you may be using the term "wind drift" incorrectly. Wind drift refers to the force of the wind acting upon the bullet in flight.

[flatsguide]

Hi P&P, it is not a false premise but counterintuitively true, subsonic .22LR loads show significantly less wind drift (wind drift as I understand it, is the effect of the crosswind component of the wind acting on the bullet) than their supersonic counterparts and the higher the .22LR velocity the higher the Wind Drift. The only reason I ask the question was to find out if the same held true for heavier and higher BC bullets launched at similar velocities.
The transonic instability is a totally separate issue from wind drift as I see it.
Don, I would gladly give up hamburgers and fries if I could dope the wind better. But was thinking that there may be a good benefit at 200 yd paper punching if one could get a 20% decrease in wind drift without the human wind doping factor.


Best, Richard

[Petrol & Powder]

While I don't dispute the results with .22 LR you are relying on, I don't think you can extrapolate those same results to heavier projectiles.
The additional variable of the transonic behavior of .22LR projectiles is not present (at least at the ranges we're dealing with) when we move up to heavier bullets.
I think there's more than one factor at play when we are talking about 40 grain .22 caliber projectiles travelling at just under or just over the speed of sound.

[Don McDowell]

Richard, I've tested and seen the difference at 200 yards with the 22 ammunition, including high velocity match. Velocity at or just under 1100 seems to be about right, of course a lot depends on whether the rifle likes the brand of ammo or not. Amazing how picky those rifles can be. The big bpcr's aren't quite as picky altho I have a couple that are just as picky if not more so than 22's.
On the mirage and wind thing it's just a matter of spending a lot of time outside watching and learning, and if you can put a few rounds down range then so much the better.
The Creedmoor cup style matches, are great learning events, where it's just you your rifle and spotting scope shooting for the score at 1000 yards. Frustrating as all get out at times, but fun none the less.

[Win94ae]

I think you're starting with a false premise.
Your statement, ".....It is well known that .22LR subsonic loading has significantly less wind drift that the same bullets flying above the speed of sound and the .22 LR loads that drift the most are the highest velocity loadings. ...." is not completely true.
.22LR projectiles that start out supersonic and then transition to subsonic speeds before reaching the target, often exhibit larger groups - BUT that's not necessarily a result of wind drift. The transonic loss of stability isn't absolutely tied to the effects of wind on the bullet.

Wind drift is the force of the wind pushing on the projectile in flight. The longer a crosswind has to act on the bullet, the greater the distance it will deflect the bullet's path.

The advantage of starting with a subsonic velocity is that the bullet never transitions from supersonic to subsonic because it was never supersonic to start with. The slower projectile will be in flight to the target longer than a faster projectile travelling the same distance and the wind will have MORE time to act upon the slower projectile. However, if the slower projectile is more stable in flight and the wind is constant (or the shooter is very skilled at adjusting for wind deflection) the projectile may still land where you want it to land.

So, you're not exactly wrong but you may be using the term "wind drift" incorrectly. Wind drift refers to the force of the wind acting upon the bullet in flight.

Drag is greater when the bullet is supersonic, and drag is a function of wind drift.

That I why I keep all my handgun bullets at 1050fps or lower. Even if I can get to 1500fps, it drifts more. I've found this out when I went from a 357mag pistol to a 44mag rifle for deer hunting; I could not understand why wind drift was easier with the pistol, until I ran the numbers. I went to the rifle because I knew it would preform better, but it ended up being worse in the wind drift department.

Run the numbers in a ballistic calculator.

[Chill Wills]

Flatsguide, you are correct in that a bullet of any size and weight adheres to the same laws of physics.
This subject requires lots and lots of text to cover I'm not up for that. IN the last 20 years this has been beat around endlessly. Which is not to say it can not be again but I will keep my part short.

Bc is Bc. Bc of .400 is a Bc of .400 - no mater caliber or bullet weight. All bullets of that Bc respond the same. Period, or they are not the same Bc.

Understand, Bc is not static. It is dynamic with velocity. This is often overlooked in these conversations.

Yes, you are correct, bullets with MV < 1100 fps have less drift than the same bullet in the 1100 to about 1500 fps range. BUT, as pointed out, there are trade-offs. As you slow the MV down, we start to see greater elevation spread on the target at distance. There are endless examples of that. In the case of very high quality 22 match ammo, very narrow velocity spreads address that and 200 meter groups can be very good.

Don is right. There are trade-offs in that to get much better high - low impacts on target at long range (BPCR) a little wind reading is called for. Take your pick. lower velocity = less wind drift and greater high/lows. Higher velocity = better high/lows and more wind drift.
Boy, I hope I don't regret stepping into this .....again .

[dtknowles]

Hi P&P, it is not a false premise but counterintuitively true, subsonic .22LR loads show significantly less wind drift (wind drift as I understand it, is the effect of the crosswind component of the wind acting on the bullet) than their supersonic counterparts and the higher the .22LR velocity the higher the Wind Drift. The only reason I ask the question was to find out if the same held true for heavier and higher BC bullets launched at similar velocities.
The transonic instability is a totally separate issue from wind drift as I see it.
Don, I would gladly give up hamburgers and fries if I could dope the wind better. But was thinking that there may be a good benefit at 200 yd paper punching if one could get a 20% decrease in wind drift without the human wind doping factor.


Best, Richard

I see in your charts that the slower bullet has a higher BC. Are they the same bullet but the BC of the bullet is higher as sub sonic than at super sonic.

[Win94ae]

I see in your charts that the slower bullet has a higher BC. Are they the same bullet but the BC of the bullet is higher as sub sonic than at super sonic.

That was a bad example to display the effect. You can always play around with the numbers yourself.

https://www.hornady.com/ballistics-r...ics-calculator

[flatsguide]

Chill, I was not aware of vertical displace of hits at low velocities. I’m aware of the need for low velocity variations, ES, to prevent vertical stringing. The way I’m reading your reply that vertical stringing is more of a problem at low subsonic velocities.
Found this on Sierras site.
“The ballistic coefficient values in the three figures exhibit strikingly similar behavior with abrupt changes near the speed of sound. Perhaps the data in Figure 4.5-3 for the .44 caliber 240 gr JHC best illustrate this characteristic. If the bullet starts at a velocity near 1300 fps, the ballistic coefficient is nearly constant until the bullet slows to about 1160 fps. At this velocity the ballistic coefficient rises abruptly as the bullet slows to about 1140 fps. Then the ballistic coefficient falls precipitously to a minimum value which occurs near 1100 fps. The ballistic coefficient then rises dramatically to a second peak value which occurs near 1050 fps. As the bullet slows below 1050 fps, the ballistic coefficient decreases in value, but in a less dramatic manner.”

Anyway BC is always velocity dependent and changes with changes of air temp, pressure and humidity.
Richard

[dtknowles]

That was a bad example to display the effect. You can always play around with the numbers yourself.

https://www.hornady.com/ballistics-r...ics-calculator

I wonder about the calculator. How does it handle BC. Does it account for changes in BC as the velocity changes. It asks for a BC as an input field. What do I put there, the BC at muzzle velocity. Where to get good BC data, I doubt the results because of garbage in garbage out.

Tim

[flatsguide]

Tim, I had the same thoughts as well.

[Don McDowell]

The online calculators will get you close and give you a fair idea of what to expect. But there isn't a one of them that will tell you what to expect when your line flag is going left to right, the flags about half way down the range are pointing at each other and the flags at the target are pointing straight up. The mirage showing consistent right left..
The Wind Chart that Shiloh sells is about as good as you can get.
Sometime just sit and watch a flag, such as a US or State flag on a flag pole, and take particular notice of how the flag flops compared to what you feel on the ground where your sitting, and take particular note of how the ripples in that flag are not consistent.
Tons of things shooting related can be learned by simple observation in non shooting related places.

[Lead pot]

The best ballistic calculator is you with your rifle, a good spotting scope and a target down range 600 yards or more.
I have spend hours sitting in my back yard with a target at the far fence line 730 yards over the bean field watching the condition changes and looking at a wind anemometer and watching the mirages firing a shot.
Set a no wind zero early in the calm morning air and wait for the ground warm up and watch the mirages starting to roll and fire a couple shots when the condition is the same drive down and mark the hits and recording them. Shoot again when the conditions change and repeat the recordings. Do this without making a sight change.

now I have a drone that takes very good photo's and I can send it down range and it will do the running and recording

Doing this is better than a calculator, this is on the job training what conditions will do to the bullet drift and how far it drifts with the change you watched.

As for the high or low velocity drift with the .22, put up a target watch the conditions and shoot.

[dtknowles]

The online calculators will get you close and give you a fair idea of what to expect. But there isn't a one of them that will tell you what to expect when your line flag is going left to right, the flags about half way down the range are pointing at each other and the flags at the target are pointing straight up. The mirage showing consistent right left..
The Wind Chart that Shiloh sells is about as good as you can get.
Sometime just sit and watch a flag, such as a US or State flag on a flag pole, and take particular notice of how the flag flops compared to what you feel on the ground where your sitting, and take particular note of how the ripples in that flag are not consistent.
Tons of things shooting related can be learned by simple observation in non shooting related places.

The point was to understand if subsonic loads have less wind drift than supersonic loads at moderate velocities. I think it is clear that the time of flight advantage that a 3000 fps load has over subsonic loads over comes any advantage the subsonic load has in ballistic coefficient. It is clear that subsonic loads have a wind drift advantage over transsonic and low supersonic loads but do they still have an advantage vs.1800 fps load or a 2500 fps load but I guess the 2500 fps load is not something you can get with Black Powder.

[Chill Wills]

Chill, I was not aware of vertical displace of hits at low velocities. I’m aware of the need for low velocity variations, ES, to prevent vertical stringing. The way I’m reading your reply that vertical stringing is more of a problem at low subsonic velocities.
Found this on Sierras site.
Richard

Good morning Richard,
Correct. As an example, a 20 FPS ES as started from accurate BPCR ammo, producing 1050 FPS (MV) will show much greater vertical on the long targets as compared to equally accurate ammo producing a 20 FPS ES starting at 1300 FPS.
Additionally, when you add in head and tail wind components, they will adversely effect the slower ammo as well, showing up as much lower or much higher hits when compared to higher velocity ammo.

Again, it comes down to trade-offs. If you were to graph the different effects and overlay them, it turns out the "X" in the data for black powder driven ammo (BPCR) puts the sweet spot in the 1250 to 1350 FPS range for shooting targets at the 600y to 1000y distances. It is also "not bad" for closer targets too, but backing off a little velocity for the 200m to 385m targets does not hurt a bit either. This is somewhat subjective group think, but reflects the mainstream of national level match competitive ammo used.

There are two books on the subject of external ballistics that will make your brain itch. from memory Robert Rinker and the other is Pijsa maybe? I can check the book case if you are interested. It is both fun and dry reading. ...An immense amount of info to wrap one's head around but has useful info.
-Michael Rix

[Don McDowell]

Trying to correlate what happens with modern high-power bullets and BPCR stuff will cause no end to the grief.
I'm setting here watching the annonometer on the cheap plastic weather machine, and see enough of a speed change to need a 4-6 minute change on the windage knob with at least a 1-2 minute change just during the time of flight of the bullet.
Static calculations on a computer are great, but they are no substitute for the real world thing.

[Win94ae]

The point was to understand if subsonic loads have less wind drift than supersonic loads at moderate velocities. I think it is clear that the time of flight advantage that a 3000 fps load has over subsonic loads over comes any advantage the subsonic load has in ballistic coefficient. It is clear that subsonic loads have a wind drift advantage over transsonic and low supersonic loads but do they still have an advantage vs.1800 fps load or a 2500 fps load but I guess the 2500 fps load is not something you can get with Black Powder.

It works exactly as I have found in real world situations.

If you play with the calculator, you find it works just as you think it would.

As soon as a bullet bow shock-wave is formed, the drag is elevated, and you get a increase in wind drift. When the speed gets to about 1600fps, the drift starts to reduce, at about 2000fps, the drift is the same as it was at 1000fps, and continues to reduce as the speed increases.

This isn't really that complicated. There is increased friction at the speed of sound, which increases drag. Once the speed gets to a point that the time of flight is great enough to overcome the friction, you get less wind drift.