Effect of calibre on windage

[curan]

I recently had a silhouette competition to shoot in particularly windy cross winds. The question was raised if a .177 pellet would be more reactive to a cross wind than a .22 pellet.

JSB exact pellets were being used at the time......

One side of the discussion said that a .22 cal, 15.9 grain pellet at 850 fps would resist the winds effects better due to the added weight.

The other side said that a .177 cal, 10.3 grain pellet at 990 fps would have less cross sectional area for the wind to react against, and as it would get there faster would not have as long to be effected.

This leads to another question - which pellet would get to the rams quicker, as the BC of the heavier pellets might lose speed less quickly?

I only shoot .177, but I hope that other AV folk might be experienced enough in both to give their thoughts..........

cheers, curan

[Camel]

I have often wondered the same with centrefires, years ago reading about the match up between the 222 and the 17 AH, I remember that the writer said they had the same trajectory and effect by wind because the higher speed and smaller cross section of the 17 cancelled out any advantage the 222 had in higher ballistics. Im no expert on that sort of thing, but it sounds good to me.

[TexNAss]

As a Bowhunter the effect of wind is bad.

To 'beat the wind' 4 main things work.
1. Getting closer- less time for the wind to push on the arrow means less deviation from the aimpoint.
2. Increasing speed- swapping to a faster bow means less time for the arrow to drift.
3. Increasing arrow weight. My 700grain buff/scrub ball arrows have inserts inside the tube. If I remove the inserts- the arrow is exactly the same externally but 300grains lighter. The wind doesn't move the heavier arrows as much as the lighter arrows. In gusty winds at longer ranges- heavier arrows are more 'consistent' than the same arrows without inserts (lighter with the same surface area).
#In my testing comparing 350grains vs 700grains arrows (with inserts)- the speed increase doesn't counteract the drift. Gusty winds give a "more random" result than an increased grouping size with heavy arrows in gusty winds. If the wind was a "constant" 10knots then maybe the benefits of speed maybe more beneficial.#
4. Shoot directly into/with the wind.

So if I wanted a 90degree wind to move an arrow inflight less (listed in order of my experience)
1. Increase arrow weight= hardier for the wind to push.
2. Go a thinner shaft, and decreased fletching sizes. Physically bigger= more surface area= greater effect on arrow.
3. Faster speed=less time for the wind to push it off target.

Tex.

[curan]

................So if I wanted a 90degree wind to move an arrow inflight less (listed in order of my experience)
1. Increase arrow weight= hardier for the wind to push.
2. Go a thinner shaft, and decreased fletching sizes. Physically bigger= more surface area= greater effect on arrow.
3. Faster speed=less time for the wind to push it off target.

Tex.

Interesting. I thought the faster speed would be more important than the lesser surface area of a thinner shaft.........

I wonder if one of the ballistics programs would give me some insight........? Think I'll go looking.

cheers, curan

[stinkitup]

I think if you run the same bullet at different velocities the faster will have less windage. I also believe weight has a good part in it.

Basically the heaviest fastest sleakest pellet is what you need So got to find the balance some where eg heavy means bigger, more surface area etc.

I was looking at my 358 bullets and 250 grains of lead doesn't move much even though its only stating life at 25/2600 ish.

I guess that is why most heavy guns use the biggest case to push the heaviest pill etc in long range bench rest.

Ryan

[TexNAss]

Let us know the results Curan.

Interested to see.

Tex.

[daisy]

I know that when shooting silhouette rams and the 177 shooters are talking about holding off an animal. I usually only hold on the edge of the ram. That's 22 cal JSBs 16g & 18g doing around 880 fps.

[curan]

Okay, I loaded the details onto the ballistics calculator on GunData.

Ignore the info on the top of the chart.....they don't include pellets, so I just used what was available, but then put in the weight and BC of JSB exact heavy for 177 (10.3 and .030) and 22 (18.1 and .027). FPS was 990 for 177 and 850 for 22. Wind was set at 10mph left to right (90 deg).

Result of wind drift at 50 was 4.10 for the .177, and 4.32 for the .22.

I ran it again at 880 FPS for the 22, and the drift was reduced marginally to 4.31.

The chart is shown out to 100 simply because the calculator will not work on less than 100.

cheers, curan

[stinkitup]

Have a look for chairgun, now that Hawke own it its still very informative and ballistics deisgned for air rifles / pellets etc

[aaronraad]

Time of flight (TOF) and Mass are the main parameters from my understanding.

Same MV + same BC + same Mass = same TOF + same Wind Deflection

Same MV + same BC, but (Mass1 > Mass2) = same TOF, but the heavier Mass1 will have less Wind Deflection than the lighter Mass2.

Conservation of Energy...or was it Momentum...or Impulse...some law Newton described anyway.

[curan]

Okay, forgive the delay, but I had to work out how to load an app on my phone to get chairgun working…….

And these figures are correct for the pellets, and now make more sense.
---------------------
JSB Exact Heavy .177
Weight 10.3
BC0.0310
Muzzle velocity 990 ft/s
Wind 10 mph @ 90deg

At 45 yards

Drift 2.9 inch
Velocity 800 ft/s
Time 0.153 sec

--------------------
JSB Exact Heavy .22
Weight 18.0
BC0.0330
Muzzle velocity 880 ft/s
Wind 10 mph @ 90deg

At 45 yards

Drift 2.6 inch
Velocity 740 ft/s
Time 0.168 sec

--------------------

So it appears that the .22 does do better in the wind with .3 of an inch less drift. It also arrives with 21.9 ft/lbf versus 14.6 for the .177, which is roughly 50% more energy. it also backs up what aaronraad was saying.

Mind you, I’m not going to rush out to get a .22 for the sake of saving 3/8” drift on a windy day.

I will also say thanks to stinkitup for putting me onto Chairgun. It’s a good tool. And I was well overdue to work out how to load apps!

cheers, curan

[stinkitup]

Which chairgun is that and what software? Ios or android. Is it the hawke version?

It is fun to see the difference weight has on trajectory and drift. I weighed a couple of bullets that I intended for 1000yds and with .1 gr difference was quite a difference at that distance in drift.

[curan]

Which chairgun is that and what software? Ios or android. Is it the hawke version?

It is fun to see the difference weight has on trajectory and drift. I weighed a couple of bullets that I intended for 1000yds and with .1 gr difference was quite a difference at that distance in drift.

It's "Chairgun Pro V1.2.5 for Android"

(whatever that means! )

[stinkitup]

Thanks mate when looking for it before it wasn't on android will go take a looksy.

[Yrrah]

Okay, forgive the delay, but I had to work out how to load an app on my phone to get chairgun working…….

And these figures are correct for the pellets, and now make more sense.
---------------------
JSB Exact Heavy .177
Weight 10.3
BC0.0310
Muzzle velocity 990 ft/s
Wind 10 mph @ 90deg

At 45 yards

Drift 2.9 inch
Velocity 800 ft/s
Time 0.153 sec
-------------------
JSB Exact Heavy .22
Weight 18.0
BC0.0330
Muzzle velocity 880 ft/s
Wind 10 mph @ 90deg

At 45 yards

Drift 2.6 inch
Velocity 740 ft/s
Time 0.168 sec

--------------------

So it appears that the .22 does do better in the wind with .3 of an inch less drift. It also arrives with 21.9 ft/lbf versus 14.6 for the .177, which is roughly 50% more energy. it also backs up what aaronraad was saying.

Mind you, I’m not going to rush out to get a .22 for the sake of saving 3/8” drift on a windy day.

I will also say thanks to stinkitup for putting me onto Chairgun. It’s a good tool. And I was well overdue to work out how to load apps!

cheers, curan

Curan, some may be puzzled by the data that indicates that the .177 drifted more, 2.9 inches to 2.6 inches for the .22, but in fact actually took less time of flight and so was "exposed" for less time. Nor does the answer lie completely in the weight difference

So we have to find a reason. The reason lies in what is known as "delay" or "lag" time which is defined as the difference in time between the actual time of flight, tof, and the time that the pellet would have taken if shot through a vacuum. So we must subtract the last from the first to get "delay or lag" time.
So taking your figures: in a vacuum the .177 at 990 fps would not lose any velocity so would take 0.1364 sec to travel the 45 yd/135 ft (135/990). The "lag" time is therefore tof - tof in vacuum or .153 - .1364 = .0166 sec.
For the .22 pellet with mv 880 fps and BC 0.0330 tof in vacuum is 135/880= .1534 sec. The "lag" time therefore is .168 -.1534= .0146 sec.

So with less lag/delay time for the wind to effectively affect the flight, the .22 pellet has drifted less even though it started at a lower mv and took longer to get there.

The real secret of this lies in the better BC of the .22 pellet.

Now, we know that pellet shape too has a lot of influence over pellet BC, not just its weight. There are many .22 pellets that are heavier than some .177 pellets but that, because of their shape and sectional density do in fact have lower BC values. One example is the .22 Crow magnum versus the .177 Heavy in your data.

The CM has a BC of approx 0.022 and also weighs 18.1 gr same as the 0.22 JSB in your data. The tof in a vacuum would be the same 0.1534 sec as the JSB .22 if mv was the same because in a vacuum there would be no loss of velocity for either pellet. However because of its worse BC the actual tof of this pellet would be 0.176 sec according to Chairgun. ...
Subtracting vacuum tof of 0.1534 sec from 0.176 sec we get a lag/delay time of 0.023 sec compared to 0.0146 sec for the JSB .22 pellet and 0.0166 sec for the above .177 JSB Heavy.
Now we see that the heavy Crow Magnum .22 pellet has a much greater lag time and therefore is it a surprise that Chairgun indicates that it will drift ... a whopping 3.91 inches, for your example at 45 yd/135 ft, compared to the .177 pellet drifting 2.98 inches, and the .22 JSB of the same 18.1 gr weight as the CM and same mv 880 fps drifting 2.6 inches!

So it isn't as simple as saying the pellet with the least actual time of flight, or the heaviest pellet, will drift the least in a given wind.

Best regards to you and any other readers, Harry.