El Lobo
You are correct, it's all theory and approximation...use 3 different drag models, with all things being equal, they will produce 3 different trajectory(s)
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El Lobo
You are correct, it's all theory and approximation...use 3 different drag models, with all things being equal, they will produce 3 different trajectory(s)
And if you're using 3 different models, at least 2 of them will be wrong for the application anyway ;)
The real issue is that no one noticed the big mistake in my density theory...it was sort of a trick question.
Two 6mm bullets of equal shape & size ( was using the 117 DTAC for my example) one weighing the normal 117 gr and the other 234 gr, made out of something of with specific gravity greater than Tungsten, could never have the same BC because they have the same form factor.
The 234 gr version would have a BC of around 1.4 because of the double density, or twice that of the 117 gr DTAC, which has a .700 BC. It's the direct proportional correlation of density/weight to BC
BC by definition is the ratio of a bullets sectional density to its coefficient of form or form factor and it can be written as:
C = SD/i = w/id2
Where C = ballistic coefficient
SD = sectional density
i = form factor
w = weight of bullet, lbs.
d = diameter of the bullet, in. Sq
Form factor can be found in design by precise measurement of the projectile or by using a chart. In practice it's confirmed by doing a controlled environment/range firing of the bullet with two chronographs positioned in the trajectory and/or radars.
Now if we run the 6mm 234 gr DTAC with 1.4 BC through a Ballistic model? :cool: I just wanted to make sure everyone understood weight really does directly impact BC when all other things are equal.
If you want to read a good article on density, twist rates, and external ballistics Daniel Lilja has a great one:
http://www.riflebarrels.com/articles...al_bullets.htm
I was working under the assumption that the BC was held constant meaning, by definition, that for the bullet weight to increase the form factor number had to get worse. Happens in the real world all the time.
Howa's 1500 in .223 is sold in a 1:12 twist rate. Stevens 200 in .223 uses a 1:9 twist rate. Can anyone make a guess why the two companies use radically different twists for the same caliber?
Jamie I knew that it did I just posted they article since I thought it was an interesting read, I have been saying it for a long time and have my own personal data to back it up.
Tanks Dean
Your definition is ture only if the form factor increases, but with the correct design form factor normally decreases. By caliber the lowest form factor bullet will have a very high SD, and therefore weigh more.
Try reviewing the highest BC bullets by caliber, as the BC increases, so does the sectional density of the bullet, plus the form factor stays close to the same or is reduced. Form factor is completely related to bullet shape, but it takes material to design it.
That's how the heavy bullet does better in the wind rule got propagated and misunderstood, the rule is true when form factor is not disregarded.
With two pieces of information about a bullet, caliber & BC, one can extrapolate the bullets form factor number.
Again, I suggest reading Dan Lilja's article...
WOW ,no two barrels are EXACTLY the same , TOO MANY VARIABLES , it should slow the bullet down (fast twist ) BUT in real life poa to poi I think other more important factors should be trained for .
Excellent to see others as I am .
Gary macdonald
So while I have your attention , and not wanting to change this thread about velocity , did anyone read the new one about lead free primers and velocity loss and excessive barrel wear ? The thinking behind this one is the lead in the barrel (primer) lubricates and reduces friction much the same way leaded gasoline use to . I hope someone else read it . And no i didnt bring it up to raise blood pressure,just because by your responses you have a much greater grasp on these subjects than most .
Thanks Gary
Howa sees their rifle as a varmint rifle and Savage/Stevens sees theirs as a more flexible rifle able to be used as a varmint rifle or for longer range work with the intermediate length/weight match bullets or able to shoot the longer monolithic bullets that some folks like for deer.
I understand everything in the article. I also understand the relationship between form factor, bullet weight and caliber. My point was that just because bullet weight increases the form factor number doesn't automatically get better and the BC doesn't necessarily increase. In some cases it does. Hornady has done some really interesting design work in the last few years along with Berger in optimzining form factor to make bullets that have a very high BC but are not super heavy. The .224cal 53gn Vmax is one example and the .308cal 208gn AMax is another. In both cases the bullet ends up with a BC that is equal to or higher than heavier bullets in the same caliber. Their relatively light weight and short bearing surfaces mean that they can be shot much faster than a heavier bullet and their high BC means that they do a very good job of retaining that velocity and resisting wind drift. The little Vmax will almost mimic the trajectory and wind drift of the 69 SMK out past 500yds. The 208 Amax will vastly outperform pretty mcuh any other .30cal bullet at long range.
The idea that heavier bullets do better in the wind is completely born of the gross lack of understanding that most shooters have about external ballistics. Guys that have studied the long range shooting challenge have a better understanding than most, but even some of them don't get it.
I have two 6-284s one is a 1-8 and the other is a 1-10 because of the range of bullets that they will shoot and the type of shooting I do with each one....
I also have a 22-250 that has a 1-14 and a .243 with a 1-10 each work for what I do with them, and every barrel is a custom order, with 27 inches as the shortest of the barrels....
Best advice, decide what you are going to shoot with it, majority of the time, look at the barrel makers charts, study and understand the bullets available, and the subsequent ballistics for the sum of the components....