Wind drift verses Area verses speed.????

[native hunter]

G"Day All
I am not a expert on this subject, hence my question.
There has been plenty of talk on many forums about how wind effects bullet drift and what effect it has on different diameter bullets and the effect as opposed to the speed of the bullet.
IE-A smaller diameter bullet will have less side area so there fore it should be less effected by side wind, also if this bullet is travelling at a considerable faster speed it will have less travel time to be effected by wind.
In saying that a larger diameter bullet will retain more speed further down range and having a bigger suface area it should be effected more by wind.???
So why are all long distance rifles larger calibres.???
Would it be better to use a smaller calibre.???
I know there is a Ballistic co-efficient(spelling) that comes into play here but dont know much about it.
So what are everyone thoughts on wind drift verses bullet area verses bullet speed.?????
Regards
Damien Webb.

[Ned Kelly]

G'Day native,
I'm no expert but am dabbling in LR shooting, from what I see, you must consider the inertia of the bullet, heavier bullets need more force to move them sideways lighter bullets do not. So they accordingly have less wind drift when shot side by side.

So the speed that you can push any bullet plus their BC go towards whether they are a wind beater or not. Also the faster you drive a bullet the more fouling you may get and the loss of accuracy to fouling will negate any gain from speed. So barrel burning speeds seem to be avoided and moderated 2800-3100fps are the norm. If you can clean regularly after say 10-15 shots you can drive them harder like they do in 500m fly and LR BR. Most VLD bullets seem to prefer the 3000-3200fps as a max anyway probably due to the risk of them blowing up if driven harder

Whether the BC is related to the inertia I dont know but the BC always seems to be higher in heavier bullets, therefore less drift. BC seems to be the rule of thumb for long distances.

the F class forum http://www.ozfclass.com/ can help with this subject.

hope this helps,

Cheerio Ned

[Tony Z]

Without going into the why and wherefores of wind drift too much, very simply wind acts on a projectile during its time in flight to the distant target. The difference of a starting velocity and an ending velocity at the target or the shorter the time taken to reach a given target the less wind drift there is or less time for the wind to work its force on the projectile to put it another way. So there are two ways to tackle this effect, take a given bullet and drive it hard or take a bullet of higher BC and let its sleek profile cheat the wind. BC can be simply explained as a bullets abilty to shed velocity from a given launch speed to a terminating speed. The less velocity shed gives that bullet a higher BC and vise versa. So in effect it is time of flight. A bullet of a low BC driven to 3500 fps and a bullet of a higher BC driven to 3000 fps could show similar wind drift. But take the lower BC bullet and launch it at the same 3000 fps and the wind drift becomes worse compared to the higher BC bullet. What has changed is the time of flight even though they have started off at the same speed.

The problem all long range shooters face is getting the balance of BC and accuracy right for the task ahead. Many first timers at LR go for the .600+ BC bullets and then try to fit that to a hyperspeed cartidge. I have rarely seen this combination work. A common choice is the 338 cal 300 grain SMK at .690 BC in a case like the 338 Lapua Mag. High BC coupled with high velocity should equate to high performance at LR. The reality is that i have not seen this work and the statistics in this country show it. My advice for LR is a bullet of .500 BC or therabouts at around 3000 fps or thereabouts is the area that should be looked at and once you have that, concentrate on accuracy both of the cartridge and of the shooter. 6 BR, 6.5/284, 284, 30/284 are all good and proven choices in a LG application with a whole array of bullets to choose from.

To answer your point directly, BC is more a measurement of time of flight than anything else and the books and experts tell you that a 6 mil 107 SMK at 3000 fps with a .525 BC will show the same drift and drop as a 30 cal 190 grainer also of .525 BC at 3000 fps. Personally i don't agree entirely as i believe that RPM and twist rates play a very big part in the whole scheme of things and my preference has and always will be to go with the lower RPMs which usually means slower twist rates and also usually means the bigger calibers. But not when it comes to .338. There is an anomally there somewhere.

Tony Z.

[Rinso]

Native,

TonyZ as usual explains it all pretty well. As you may have noticed from time to time those of us shooting 30cals bait the 6mm or "pop gun" brigade pretty badly.

You will also notice that things like the 6mm Dasher are "popping" their way into more and more podium finishes. A good example would be the Batemans Bay NSW shoot in June past when a 300 Win Mag won over a 6mm Dasher by a mere 2 points.

There are several schools of thought on the how's and why's as Tony discussed and it all gets fairly complicated.

Any Fullbore shooter will tell you that a 223 with a 1-8 twist barrel shooting 80grn pills with a good load will match a 308 1-13 twist shooting 155's.

I have seen almost every calibre you could imagine and a few you couldn't tried at Long Range BR some work better than others and as Tony says the ballistics tables and maths all go out the window in some cases. A massive overbore like the 257 Banshee (8x68 necked down to 25 cal or 30-378) dont seem anymore succesful than the rest even though they produce a small bullet at very high speed. Then again neither does the 338L with 300 grn MK stand above the field.

At the end of the day you need to decide wether you are happier with a small bullet ie 6mm or a big bullet ie 30 cal .. each has its merits. Also a factor are things like speed over BC. If the bullet gets there quicker the wind has less effect ... if the bullet is bigger with a better BC the wind has less effect .. So why is aJR shooting 187BIBs in the 300RN shouldn't he be running lighter bullets that go faster ???

If these maxims were absolute we would all be shooting the biggest fastest calibres we could find with the lightest pills we could manage, but then explain a 30BR turning up at Townsville and shooting small group and highest scoring target ... Not fast, not small ... go figure.

It all comes down to operator error at the end of the day IMHO The really good shooters will still do well with whatever they have and the rest will still struggle for that one really good score no matter what they have. Equipment IS important but it only does so much .. the biggest variable in any rifle is not in the rifle or the quality of ammunition or the type of rest used but rather in the shooter. Technique, wind reading, patience and good temprament will do you more good than slightly better BC's or equipment.

That does not really help you much I know but then thats why Long Range BR is so much fun .. you could win with a bent pipe and blow dart if you pick the right condition to shoot on.

cheers
Rinso

[Tony Z]

"If these maxims were absolute we would all be shooting the biggest fastest calibres we could find with the lightest pills we could manage, but then explain a 30BR turning up at Townsville and shooting small group and highest scoring target ... Not fast, not small ... go figure."

Sometimes even a blind squirrel finds an acorn on the forest floor. Bob M may not agree .

Tony Z.

[Ackley Improved]

deleted

[Ackley Improved]

DANG.. the blind squirrels are finding some acorns !











Come on, thats worth a giggle.. isn't it???

[Dr G]

DANG.. the blind squirrels are doing well !











Come on, thats worth a giggle.. isn't it???

umm....


Nope

[Ackley Improved]

Dr G.. not a popgun shooter huh?? Not a blind squirrel either then?


How I see it, BC vs wind drift.... for LR, BC over .5, velocity at around the 3000fps, then its all up the trigger puller!

Cheers
AI