Excuse for my english, I'm from Italy.
My question is about B.C. vs bullet weight.
I don't know if high ballistic coefficent means best crosswind resistance or bullet weight is more important.

Ex. 6.5 x 55 140 Sierra MK (B.C. .526) 2650 fps
308 W 168 Sierra MK (B.C. .462) 2650 fps

Which bullet pay more for crosswind deflection?

Thank you guys

Great forum

Genoa,

Put you numbers in JBM Balistics Calculator.

http://www.eskimo.com/~jbm/bibliography/bibliography.html

At 600 yards a 10 MPH crosswind will move the -
6.5/140 SMK 28.9"
308/168 SMK 36.0"

Looks like the B.C. is the more important factor.

A better way to compare would be to eliminate most of the differences between the bullets, leaving only the BC as the determining factor.
Say a Speer 165gr rnsp (BC=.274) and a Nosler 165gr BT (BC=.475)

To keep it simple, BC is a measure of how much a given bullet slows down when compared to a "standard" bullet launched at the same velocity over the same distance under the same conditions.
A bullet that slows down 4 times as much has a BC of .250, one that slows twice as much has a BC of .500 and one that slows only 1/2 as much has a BC of 2.000. Caliber and weight are not part of the BC calculation formula.

All else being equal a bullet with a higher ballistic coefficient will fly flatter and be less affected by wind than a bullet with a lower ballistic coefficient. This because it retains velocity better due to its shape.

Bullet weight and velocity comes into it as well.

A better comparison would be 2 bullets of the same weight but different styles.

Example, 2 x .308 150gn bullets both leaving muzzle at 2500 feet per second.

Round nose bullet with a Ballistic Coefficient of 0.227 is still doing about 1324 feet per second at 400 yards and has dropped about 72 inches and in a 30 mile per hour cross wind from 9 o'clock has gone sideways about 103 inches.

Hollow Point Boat Tail match bullet has Ballistic Coefficient of 0.417 and at 400 yards is still doing about 1701 feet per second and dropped about 58 inches and drifted sideways in a 30 mile per hour cross wind from 9 o'clock about 53 inches.

Both bullets same weight, calibre and starting/muzzle velocity.

See website www.exteriorballistics.com which is a site by Sierra Bullets ( www.sierrabullets.com ) and is excellent.

I did these figures on the Sierra Infinity Ballistic calculator. You need to buy it, its not free but worth the money and easy to use. You can set it to work in metric measurements, not sure about the language options.

Ran the figures for the bullets you mentioned at muzzle velocity 2650fps.

6.5 at 400 yards velocity is about 2016 feet per second, drop is about 48 inches and wind drift about 35 inches using a side wind at 30 miles per hour from 9 o'clock.

.308 as above at 400 yards velocity is about 1906 feet per second, drop about 49 inches and wind drift about 42 inches.

Regardless of what the computer says best to check on targets! Having said that I have found the computer is pretty close every time.

Thank you very much for your help!!

I use the free Point Blank Ballistics Program which I down loaded from http://www.huntingnut.com Take a look at it ,I think its the best Iv found on the net.

Genoa, I installed the Sierra Infinity ballistic program onto my notebook computer, mainly so I could observe the installation process.

There are a number of language options at the installation stage including Italiano so this may be of interest to you. Once installed you can switch between metric and imperial units as you wish which may also be of interest.

I also ran the numbers on the 2 projectiles that you mentioned but at 600 yards and with a 90 degree a0 miles per hour cross wind as RaySendero did and got results within half an inch of his so both programs are in good agreement.