Wind drift in the real world.

[Big Al]

Guys,

 

I remember missing a shot last year which really made me think about the effects of wind drift and the need for accurate wind reading or the difficulty we face if the wind changes once committed to the shot. Basically the wind dropped from 4mph to 3mph on a 360yd face on crow, I saw the bullet strike just down the side and it was as close to being a hit as I could imagine.

 

When I looked at the figures for the shot I was quite surprised, my Shooter app suggested two click less for the 1mph drop in the wind 1.5moa instead of 1.9 moa, that equated to a POI shift of 1.5 inches. Taking a centre mass shot on a crow that is barely 3" across really showed me just how easy it can be to miss even before we remove human error. Before this point I had been steadily increasing my distance and confidence with more hits than misses as each shot was considered carefully, this really was a wake up call to what is possible. The rifle was a 9 twist .223 firing 55r SBK's which left me thinking how much more likely I might have been able to turn that miss into a hit with a caliber that rode the wind better.

 

I spend quite a bit of time last autumn looking at BC's and running ballistic calculations on different calibers within the caliber range I wanted to remain which was the smallish calibers of .224 or below, maybe a 6mm at a push. I finally arrived at a 20BR firing 55r Bergers with a BC of 0.381. Ive since bought the 20BR and am close to having the 55gr load worked out with 0.5 moa at 100yds and sometimes a bit better, these are running at 3450fps and I feel confident I can improve on the accuracy with a little more work.

 

Now comparing the drift at 400yds with my old .223 is quite interesting as you can see below;

 

.223 was 23.6"

 

.20BR is 11.0"

 

As you can see the theoretical difference is just less than half. So with that same shot the 1mph difference would have been only a change of 0.2 moa from 0.9 to 0.7 and that would have changed the POI by only 3/4 inch at 360yds assuming all other things were equal and that would have been a hit on a 3" target.

 

Now I accept all of this is theory but then again theory is important as it helps us to make informed decisions, yes I have had to take into account that the BC's are true which I accept they may not be, Ive used Litz BC's to try and at least be as accurate as possible. For those who don't buy into the accuracy of comparing BC's please don't waste your time telling me this as that is a whole different discussion. Quite clearly even if the BC figures are a bit off the fact still remains that a .20 55r Berger will considerably out perform a .224 55r SBK at appropriate velocities and that is my point which then begs this question;

 

Do you guys who shoot accurately over distances of 300yds think I will see a real world difference in my hit rate by changing to the 20BR?

 

I ask this because Im also looking to build another rifle in the .224 or smaller range and when looking at the likes of a .20 Practical shooting 39gr SBKs Im already freaking out because the drift starts to wander back up towards that of the .223 albeit only 15.6" @ 400yds.

 

 

[247sniper]

Hi Al,

 

In answer to your question.....yes you will notice a difference. As is fact, out to 300-350 velocity is king, past that range BC starts to take over and increasingly so at greater distances.

 

My .204 is awesome out to 350 yards and rabbits in and around a 10 mph wind out to this range are in massive trouble, I hit 90% of them with first time cold bore shots. After 350 yards everything changes, velocity decreases and BC decreases etc and then i start to experience what you have experienced, little wind change leads to massive down range Wind drift.

 

Ok moving on, last year I build a .223 Ackley improved with a fast wist shooting heavy high BC 80 grain Amax, as Brain Litz suggests their manufactures BC was or is underestimated. With a G1 real life BC of 0.472 I have extended my long range hit success considerably. I haven't done much rabbit shooting with it yet but i sure will this year now I have a awesome load sorted for it. Last year I dialed a shot for a 580 yards rabbit in a 12-15 mph wind, i had done plenty of gong practices out past this range, I shot 1x rabbit out off a group of three, the other two rabbits remained so shot another one....the third rabbit ran slight closer towards me at 571 yards, I made a small adjustment and shot him as well knocking all three over with for three shots . a memory that will last a life time. These bullets are ssoooo stable in the wind. I caught it all on camera as well but this forum would not want me to share it on here.

 

This year the the rabbits are going to get it lol, i was practicing on steel last week end at 880 yards, see my other post on here and photo of group size 10 shots and all on steel, would of resulted in 10 dead rabbits anyway at 880 yards.

 

Steve.

[gbal]

Al,Steve is spot on wrt to the first 350 yards or so-velocity matters,but thereafter so much is being lost,BC becomes the bigger factor (of course BC was also there out to 350,it's just that very high velocity masks some effects).

It matters little which BCs (G1 or G7) are used at these distances,and not at all for comparison of bullet purposes (though if the G1 especially are 'massaged' differently by manufactures ,it does not help).And anyhow,you are pretty well obliged to use published figures-Bryan Litz' are probably the most consistently accurate.

Check your ballistics program is sophisticated enough to include some of the raft of error variables-you will have a half inch of combined Gyroscopic drift and Coreolis effect by 300+,and of course the intrinsic precision of the rifle comes in.There is no way that a 1/2 moa 100y rifle will shoot less than 2 inches at 400,and even a 1/4 moa at 100 is pushing an inch by 400. These are absolute minima.The actual group dispersal is often considerably more than just prorata though.So there could be an inch between rifles in intrinsic precision-and that is pretty close to a potential miss for that rifle(the 3/4 moa at 100 rifle is just not good enough-that alone gives an absolute minimum shot dispersal of 4 inches at 400y-50% + misses,before any other errors are included!

 

The good sixes will win out-but they have to be 'good' ie not give up any precision....so PPC for these distances,and 6BR might extend them.Terminal bullet performance seems not too critical on crows,which helps. Heavy 224 class too,if you can get extra case capacity.

And no wind.

g

[Big Al]

Hi Al,

 

Ok moving on, last year I build a .223 Ackley improved with a fast wist shooting heavy high BC 80 grain Amax, as Brain Litz suggests their manufactures BC was or is underestimated. With a G1 real life BC of 0.472 I have extended my long range hit success considerably.

 

What speeds are you getting Steve and for how much powder?

[247sniper]

25 grains of powder and my load is doing 2960 ftps Al.

 

Steve.

[Sherlock]

 

 

Do you guys who shoot accurately over distances of 300yds think I will see a real world difference in my hit rate by changing to the 20BR?

 

.

 

 

 

Yes - The 20 BR launching the very high BC 55 grn Berger will easily out muscle a 223 shooting standard 55 grn bullets.- That's a given. You have obviously and carefully selected this calibre and bullet combo to do this.

 

As with all over bore cals ( which the 20 BR most certainly IS) The sacrifice is, you will probably get little over 1000 shots of best accuracy out of your tube. My pal shooting the same calibre and bullet got 800 rounds and his barrel was totally shot out - Albeit , he pushed his harder.

 

I run a 223 - shooting 55 grn SKB's at 3400 fps - I also run a 22.250 that launches the 80 grn Amax at 3320 fps.. The 22.250 is a totally different beast and the first shot hit ratio at 500 + yrds is significantly higher. My 22.250 has similar ballistics at 200 yrds , too Steve's 223 AI at the muzzle...

 

I am in the same boat - the 22.250 will have a shortish barrel life compared to the 223 (or 223 AI) - but the big 22 cal gives fantastic long range performance and is great in the wind - My previous tight twist 22.250 was still shooting crazy tight groups at 1200 rounds when I re-barrelled it into 6mm cal ( big mistake) - The 22.250 but did have fire cracking in the throat but still shot fantastically well.

 

For ranges under 400 yrds I find that the 223 is easily sufficient - I just take note of the wind conditions - If its howling the 223 stays in the cabinet - and the 22.250 is used.

 

As said by Steve and Gbal - for shortish ranges - 300 yrds and less - a high velocity bullet will work in all but the worst of conditions,

 

 

ATB

S

[camo304]

25 grains of powder and my load is doing 2960 ftps Al.

 

Steve.

 

I should learn to read lol

[shuggie]

Hi Mate shooting long range is a very hard task,first shot kills on small targets are rare,they can be done and there the ones you here about,if you are plinking on plates crows rabbits thats fine but if you start shooting out to 400yds and over you need the bullet way the best bc.to get consistent first shot kills.Most calibres out to 400yds will hit targets when you walk the shots on,i started way a small calibre but soon came round to the larger calibre way the best bc my wind drift ar 500yds is less than the 20 at 400yds so its not hard to see the advantage .Like it or not trying to get first shot kills on small targets at ranges over 400yds are not common ,try a standard clay at 400yds fire one shot a day for 7 days see how you do,the wind can be very hard to read you can only read it from where you shoot ,i mostly shoot roe deer if i see a roe on a clear fell say 400yds i would range it way a br2 g7 rangefinder which gives you air pressure height above sea level incline makes the calculation then gives m.o.a. reading and the wind in 5mph so if the wind is say 5mph cross i look at wind drift its 6.75 inches for a 10mph i then look and say can i put a bullet into a 5inch circle at 400yds my drift works out at .675inches per 1mph so if you set the wind for 5mph you have a 2mph plus or minus window to shoot .this is just a small insight hope it helps i have been doing this for over 20yrs .You want go far wrong way looking at F.Class calibres they are always looking for the best bc

[onehole]

Al ,,,highly agree with points made by Steve and Gbal,,,I would want to shoot the highest BC possible out of any given cartridge when going beyond 300 yards to leep the horizontal part of the cone of fire as narrow as possible and help negate the small wind changes that can occur from one minute or one second to the next.

If I were to thnk about building a "224" rifle at this moment in time and application for medium to longer range then I would thinking fast twist and in ascending order,,,,223,,,223 Ackley,,,22BR and using 75/80 Amax. ,,,,Regds ,,,,,O

[AnthonyR]

 

[AnthonyR]

 

Yes - The 20 BR launching the very high BC 55 grn Berger will easily out muscle a 223 shooting standard 55 grn bullets.- That's a given. You have obviously and carefully selected this calibre and bullet combo to do this.

 

As with all over bore cals ( which the 20 BR most certainly IS) The sacrifice is, you will probably get little over 1000 shots of best accuracy out of your tube. My pal shooting the same calibre and bullet got 800 rounds and his barrel was totally shot out - Albeit , he pushed his harder.

 

I run a 223 - shooting 55 grn SKB's at 3400 fps - I also run a 22.250 that launches the 80 grn Amax at 3320 fps.. The 22.250 is a totally different beast and the first shot hit ratio at 500 + yrds is significantly higher. My 22.250 has similar ballistics at 200 yrds , too Steve's 223 AI at the muzzle...

 

I am in the same boat - the 22.250 will have a shortish barrel life compared to the 223 (or 223 AI) - but the big 22 cal gives fantastic long range performance and is great in the wind - My previous tight twist 22.250 was still shooting crazy tight groups at 1200 rounds when I re-barrelled it into 6mm cal ( big mistake) - The 22.250 but did have fire cracking in the throat but still shot fantastically well.

 

For ranges under 400 yrds I find that the 223 is easily sufficient - I just take note of the wind conditions - If its howling the 223 stays in the cabinet - and the 22.250 is used.

 

As said by Steve and Gbal - for shortish ranges - 300 yrds and less - a high velocity bullet will work in all but the worst of conditions,

 

 

ATB

S

 

 

Which bullets and what load where you using in the 22-250. Also what was the twist rate of your barrel.

 

I am looking at going down this route as long range vermin gun but I have also considered the 20BR with 55gr Bergers and a 6x47 as well. 22-250 would be much easier as I already have one that is nearly shot out after about 1600 rounds.

[gbal]

Anthony,243 is just 'as easy' and a heavier bullet with superior BC and a bit more velocity (200fps approx at 800y) is going to win out ballistically-assuming there is no trade off against accuracy. Hence the larger capacity 6mms for 600+ varmints-where permitted.

It isn't essential,but it is superior.And just about as 'shootable',moderated.

gbal

[Big Al]

Anthony,243 is just 'as easy' and a heavier bullet with superior BC and a bit more velocity (200fps approx at 800y) is going to win out ballistically-assuming there is no trade off against accuracy. Hence the larger capacity 6mms for 600+ varmints-where permitted.

It isn't essential,but it is superior.And just about as 'shootable',moderated.

gbal

 

What would you consider the appropriate 6mm vermin capable bullet for this sort of thing be George and what would its speed, drift and drops be at 600yds?

[jcampbellsmith]

Anthony,243 is just 'as easy' and a heavier bullet with superior BC and a bit more velocity (200fps approx at 800y) is going to win out ballistically-assuming there is no trade off against accuracy. Hence the larger capacity 6mms for 600+ varmints-where permitted.

It isn't essential,but it is superior.And just about as 'shootable',moderated.

gbal

 

I don't have George's experience, but I do agree. http://www.accurateshooter.com/cartridge-guides/243win/ is an interesting read. Regards JCS

[camo304]

105gr Amax @ 3046 does the job

[gbal]

Re bullets in 6mm: JCS' recommended read -Accurate Shooter- 243-pretty well gives an exhaustive list of the options.Thee are genuine issues with some -115Dtac -as 'varmint/vermin' suitable,in terms of terminal performance,especially at distance.There isn't really much of a case against that bullet on ballistic grounds from a 6mm.

So we have the 105 Amax-generally accepted as an accurate bullet BC .5,and effective-might be marginal in some 243s (but so are all the heavy 224 bullets in slow twist barrels).In all cases we will need an appropriate fast twister.In a 243 AI,3300 is hottish.In a 6mmrem,3225 isn't hot;and an AI might run 3400fps. There are a very few hotter options,but that's getting specialised(though600+ crows is unlikely to be routine either).

105 scenars are often very accurate. Hornady's 100g BTHP with BC .53 might/not be suitable.The 87Vmax and older87 HPBT (BC.4,.38) are options with varmint credential designs. Bergers?

 

Some commercial loads indicate 6mmrem with 100g BC around .4 ,and 3250 fps give 17/12 D/D (10mph) at 400y and 60/29 by 600....(with a 204R managing 13/15 and 51/38 ).

 

More bang,powder,wear,and clout-of course-none of which might be desirable/necessary.

 

By 600+ any advantage starts to look attractive (hence 6.5s-though a 264 win mag 120g .46 BC @3250 only buys 16/10.2 at 400...56/25 at 6000.....but it's diminishing returns in 'efficiency' terms...

 

There's always something new coming along-green tip Sierras 90g,eg. A 115g 6mm varminter would be something!

 

gbal

[Sherlock]

 

 

Which bullets and what load where you using in the 22-250. Also what was the twist rate of your barrel.

 

I am looking at going down this route as long range vermin gun but I have also considered the 20BR with 55gr Bergers and a 6x47 as well. 22-250 would be much easier as I already have one that is nearly shot out after about 1600 rounds.

 

A few years ago , I also looked at the 20 BR firing 55 grn Berger bullets. In the end I decided against it.

Mostly due to the fact, IF the 55 grainers wont shoot accurately - or Berger discontinued them , as they have with so many bullets in their line up. There was not another bullet that had anywhere near the BC of the 55 grn pills and would expand reliably.

 

But no doubt this cal would be superb as a long range vermin round , but a bit of a risk. Plus as I run several calibres, I didn't fancy the fek about sizing 6 BR brass to 20 cal , when there was some excellent Lap 22.250 brass on my shelf ready to use.

 

The 22.250 was the logical choice for me, as I already had dies and a good working knowledge of the 22.250 having owned 5 or 6 rifles in this calibre. The addition of Lapua cases and using the high BC Amax bullets lifts the 22.250 performance into that of a larger calibre.

 

In fact I ran a 243 ( 8 twist) for some time and the 22.250 is actually better on both drop and drift than the 243 shooting 105 Amax. Examples below in 10 mph cross wind

 

 

500 YARDS

 

243 win - Bullet 105 grn Amax - MV = 3030 fps - DROP = 43.2 inches DRIFT = 16.5 inches

22.250 - Bullet 80 grn Amax - MV = 3330 fps - DROP = 35.2 inches DRIFT = 15.5 inches

 

600 YARDS

 

243 win - Bullet 105 grn Amax - MV = 3030 fps - DROP = 70.5 inches DRIFT = 24.6 inches

22.250 - Bullet 80 grn Amax - MV = 3330 fps - DROP = 58.2 inches DRIFT = 23.3 inches

 

 

The load I use at the moment is 35.2 grns of Elcho 17 behind a 80 grn Amax ( or 75 grn Amax) in an 8 twist LW tube I have also had great success with IMR 4350

 

 

ATB

S

[Big Al]

I shared the same concerns about the 20BR Sherlock but the right rifle came up at the right price so it was worth a punt for me, Ive managed to get 500 of the 55r Bergers and I know where there is another 300 sitting so all being well that will last a good while.

 

Its nice to see that the little .20 cal is there or thereabouts with the big boys for around 32gr of powder

 

500 YARDS

 

243 win - Bullet 105 grn Amax - MV = 3030 fps - DROP = 43.2 inches DRIFT = 16.5 inches

22.250 - Bullet 80 grn Amax - MV = 3330 fps - DROP = 35.2 inches DRIFT = 15.5 inches

20BR with 55r Bergers 3600fps 30.0 16.8

 

 

600 YARDS

 

243 win - Bullet 105 grn Amax - MV = 3030 fps - DROP = 70.5 inches DRIFT = 24.6 inches

22.250 - Bullet 80 grn Amax - MV = 3330 fps - DROP = 58.2 inches DRIFT = 23.3 inches

20BR with 55r Bergers 3600 fps 50.5 25.4

 

 

 

 

 

[gbal]

The post has raised some good points and there is good stuff here.I would not worry unduly about an inch or two in the ballistics-well within individual rifle variability,even if nominally same barrel length etc.

But more widely,it touches on strategic v tactical decisions.

 

I mean,there is little real doubt that ,at their bests,the 6mm is ahead of the 224 ballistically-not evry 6mm and every 224,but in overall potential. But that's strategic,not tactical.

The 6mm completely dominates the 224 in precision tactical shooting (various distance gongs etc,out to roughly 700y.) The 6mm dominates in 'across the course' three positional shooting at 300 and 600y,for score-and much R&D has gone into developing 6mms for the AR platform.I

The 6 is a better hunting cartridge in most applications(tho not all),and is more 'legal'.

The 6 is capable of competitive long range performance (1000y) where all the 224s really struggle-and are not contenders in any conditions.

6PPC is extraordinarily accurate.

OK-but in general the 6s are greedier on powder,needlessly potent in energy terms for some uses-generally small targets-alive or inanimate.They may be more restricted in UK for some purposes

by licensing. They are louder,recoil more and so on and so on.

 

Strategically then, a 6mm is the general preference-with perhaps a few exceptions.But at a 'tactical'level,it's not so straightforward.

Sherlock's post is a great example of this. The potential superiority of the 6mm is mitigated by the absence-perhaps temporarily-of a really good 'rabbit' bullet...target no problem (115Dtac) or Deer(no problem),And his data shows clearly that this reduces the 6mm to about par with one of the best 224s-the 22/250,because that does have a high BC and suitable bullet.There may/not be issues of "off the peg' availabiulity of suitable launch platforms-some 6mms are pretty much custom/expensive options only (6BR). Who can foretell future availability-I see no real problem if Varget never reappears,but others will see this possibility as needing some action. I general,continuity is not assured-though to be fair,the trend is to more and better components.But no 115 g 6mm varmint bullet-leaving the 22/250 to fill the niche for now-potentially a little less outstanding,but available now-though not an 800Y clear first choice-what is?Of course accuracy is another-largely unknown -factor-see end.

You could of course throw in minor considerations- is there a better 150-200 yard fox cartridge than the 222 (economical in rifle and ammo-and with old exposed lead soft points,even?)- and so on-but it's somewhat subjective and minor-the 223 will do it as effectively,as will PPC,BR etc.And yoy may need to consider individual differences-eg recoil tolerance,possibly local conditions etc,authority to possess,....etc

 

In theory (ballistics), theory and practice should be the same,but in practice they can differ for a variety of local/tactical reasons,most of which will prove transient over the longer term.

 

Just a final thought on accuracy/precision-there is variation within 224s and within 6mms and of course individual rifles within each. What I have not seen is a reasonably convincing-or any- study of possible distance interaction effects. By that I mean,eg-we know that you cannot assume that precision/group size is pro rata with distance (1/4 moa at 100y is not guaranteed to be one inch at 400,or 2 inches at 800-indeed the raft of dispersion variables and a wealth of experience says it is not-groups get progressively worse with distance.But is this a uniform degredation-I mean,do some calibres/bullets etc simply do worse than others and degrade more? Suppose calibre X 'resists' the shot dispersal over distance better than calibreY - that would need to be factored into any decision for distance accuracy.

 

Is a 1/4 moa 224 more or less likely than a 1/4 moa 6mm to hold 1/4 moa way out there ?

 

My guess is that the faster/higher BC (actually i7) bullets -OK 6mm-might do better,but do we actually know anything about this? Did/does 'buck the wind' have hidden factors,not simply 'drift'?

 

gbal

 

 

 

 

 

 

 

 

 

gbal

[Alycidon]

Running 55s at 3600 is a pretty high pressure load. I run 50s at 3500 and 39s at about 3650, using N150 I expect a barrel life of 1500 rounds, I doubt you will get 1000 rounds with your load.

 

N150 is my first choice powder for the cartridge having also tested N550 and N160.

 

A

[CZ Varminter]

Can I just ask,would it have made a difference if you had a scope that was on a mil based system. This click value would have been closer and not as "coarse". This why I am saving up to change my scope to a mil mil system.

 

Just putting it out there. To me theoretically, you would have had a smaller margin for a miss, if that makes sense.

 

CZV

[jcampbellsmith]

CZ. An interesting article on your question - http://precisionrifleblog.com/2013/07/20/mil-vs-moa-an-objective-comparison/ Regards JCS

[gbal]

Can I just ask,would it have made a difference if you had a scope that was on a mil based system. This click value would have been closer and not as "coarse". This why I am saving up to change my scope to a mil mil system.

Just putting it out there. To me theoretically, you would have had a smaller margin for a miss, if that makes sense.

CZV

CZ,do you mean how much does each scope click adjust POI-the finer the adjustment the more precise the adjustment possible?

 

Yes,but not sure that mil has any advantage per se over moa,since these measuring systems( cf metric/imperial) in themselves are not defining the amount/value of one click.

Target shooters often chose moa scopes (whatever advantages the mil system might have,they don't apply to fixed targets at known range). These are often 1/8 moa click value- so one click is 1/8 th of an inch at 100y....do we need any finer adjustment than that?

Offhand,I don't know how fine a click can be in the 'mil' system,but I'd imagine Bench Rest shooters might have moved to that system if it offered finer adjustment?

For field shooting though,there will be a pragmatic limit on just how small an effect on target a click produces....not least because eg 1/16 is getting very pernickety,and means an awful lot more clicks needed to dial in.....

Stalking rifles are often 1/4 moa per click....1/4 inch at 100y is not much change in POI on a deer,1/8 would be way too fussy.....

 

There is a very good case for more magnification for precision.The mil system may well be ok-but doubtful if it will offer more precise adjustment.Tactical mil scopes probably are 'coarser' by design,and tend to have less high end mag (over 25x) just as are stalking moa scopes,but overall is it not the calibration of the 'click' that matters,for purpose,not the measuring system?

Shooters of course may have preferences that have little to do with technicalities,though some do-as in reticules-the finer the better for target shooting,and likewise second focal plane.This may not be so for stalking ,esp in low light,or rapid tactical shooting at variable distances...

Better quality is always an advantage-eg a click is a click,reliably the same value.

 

gbal

PS had my morning fix of caffeine, and of course its easy to quantify,thus:

At 1000y (pro rata of course for less-500 is half ) click and poi impact relationships are:

1/10 mil gives 3.6 inches

1/4 moa gives 2.6 inches

1/8 moa gives 1.3 inches

 

so clearly the typically available moa clicks are 'more precise' IF you need/want it.

[Big Al]

Can I just ask,would it have made a difference if you had a scope that was on a mil based system. This click value would have been closer and not as "coarse". This why I am saving up to change my scope to a mil mil system.

 

Just putting it out there. To me theoretically, you would have had a smaller margin for a miss, if that makes sense.

 

CZV

 

No, it would not make any difference.

 

The issue I had was the amount of wind drift from that particular bullet and velocity combination.

[Big Al]

Can I just ask,would it have made a difference if you had a scope that was on a mil based system. This click value would have been closer and not as "coarse". This why I am saving up to change my scope to a mil mil system.

 

Just putting it out there. To me theoretically, you would have had a smaller margin for a miss, if that makes sense.

 

CZV

 

No, it would not make any difference.

 

The issue I had was the amount of wind drift from that particular bullet and velocity combination. Wind deflection will remain the same in real terms regardless of what unit of measurement you use to measure it.