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Bullet BC variation
Posted: Tue Mar 26, 2013 11:45 am
by Norm
Has anyone done any testing to see what the BC variation is from one bullet to the next out of the same box? In particular 6mm to 7mm bullets.
Seems to me that with bullets in the same box, varying in length, weight, meplat diametre etc. small differences in BC would result.
I know bullet pointing can raise the BC a bit but was wondering what the natural variation in BC there is in a box of bullets.
Posted: Tue Mar 26, 2013 12:15 pm
by johnk
I suspect that one would face a challenge trying to remove or allow for other variables.
Posted: Tue Mar 26, 2013 3:21 pm
by Norm
johnk wrote:I suspect that one would face a challenge trying to remove or allow for other variables.
You are not wrong!
The reason I am looking at this is that I will be shooting at Coonabarabran out to 1500 yards with a 7mm and am trying to determine what the "Normal" vertical dispersion should be for variations in BC over and above that for my load.
At 1500 yards, small changes in BC show up as greater amounts of Vertical dispersion than what is experienced at 1000 yards, so is of greater importance.
Just how much does a 1% or 2% normal variation in BC result in dufferences in drop at such distances and what can be done about it if anything.
Posted: Tue Mar 26, 2013 4:08 pm
by johnk
In that case, why not punch it into a good ballistic table, if you can find one that goes to 1500 yards.
Posted: Tue Mar 26, 2013 5:48 pm
by daj
Norm,
According to JBM Ballistics, for a 180VLD at 2850fps MV, varying the BC by 1% gives you around .2MOA change in elevation at 1500yds (Coonabarabran 518m)
Posted: Tue Mar 26, 2013 6:07 pm
by mike H
Norm wrote:johnk wrote:I suspect that one would face a challenge trying to remove or allow for other variables.
You are not wrong!
The reason I am looking at this is that I will be shooting at Coonabarabran out to 1500 yards with a 7mm and am trying to determine what the "Normal" vertical dispersion should be for variations in BC over and above that for my load.
At 1500 yards, small changes in BC show up as greater amounts of Vertical dispersion than what is experienced at 1000 yards, so is of greater importance.
Just how much does a 1% or 2% normal variation in BC result in dufferences in drop at such distances and what can be done about it if anything.
Norm,
I wouldn`t worry about it,the horizontal movement/wind drift, will be a bigger factor,assuming your velocities are reasonable in extreme spread.
Mike.