The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

This is the data for the Sierra Match King bullet that I propose to load in my .303. What use can I make of this data? The penultimate column is the Sectional Density and the final column the BC.

I've tried to Google and read articles in Wikipedia but I'm struggling a bit so grateful for guidance.

Watcher

BC is the more important figure as you need this to work out elevation come-ups using a Ballistics Calculator, as long as you have the velocity info

Hth
Alan

Probably the most useful way to think of Sectional Density without getting into the 'math' is in terms of 'Penetrative power' in a hunting context.

For example a 6.5mm bullet has a fairly high SD and , given a suitable construction for hunting, should penetrate better than a bullet with a lower SD...... not hugely important in most cases of UK hunting!

As for BC... its effectively a measure of bullet 'slipperyness' through the air and also of retained down-range velocity...... try to find the G7 value rather than the G1 (it is more representative of actual 'drag' on the bullet over range & speed changes until it hits the target) and use this in a ballistics program to help calculate bullet drop and scope clicks required to get on target.

Thanks Dave,

That helps. I'm not clear of the difference between G1 and G7; where would I find that?

W

Watcher wrote:Thanks Dave,

That helps. I'm not clear of the difference between G1 and G7; where would I find that?

W

G1 is typically quoted as the BC 'Standard' and its related to what is called a standard projectile (Old fashioned flat-based bullet that looks like what you would think of as an artillery shell)..... BUT..... it is not a truly valid value except at a given speed (High/Max Muzzle velocity) and it does not account for changes in that G1 BC value as the bullet slows...... therefore it is an approximation of what is really happening.

G7 values reflect a modern projectile shape (typically boat-tailed) and most accurately reflect the true drag on the bullet between it leaving the muzzle and slowing as it goes downrange.... so by using this you get better results from a ballistics program.

You should be able to find these on the web (manufacturers sites or reloading books in some cases) I will try to provide the G7 for you ...what bullet was it?

Dave,

You're very kind. Its the Sierra Match King 174 grain .311 inch (Part No 2315).

W

Can't immediately find a G7 for your chosen bullet but will keep looking.

If no luck then you can enter the range of velocity related G1 values show by Sierra to programs like Bulletflight to reflect a 'degrading' BC as the bullet slows down in flight.

Any 303 shooters out there that can help short-cut the search for a G7 value on this bullet?

There is a free web site which is called JBM Ballistics,I think you may find a lot of information your looking for there

Thanks for all your help chaps; appreciate it.