Long Range and BC - What Difference Does It Make?

[rsterne]

I started this thread so I wouldn't pull another off track.... There are a lot of misconceptions about what the Ballistics Coefficient can and cannot do for you.... Here is the summary....

1. It makes little difference in trajectory, until you really start stretching out in range.
2. It makes a huge difference in wind drift. Twice the BC, half the wind drift.
3. It makes a huge difference in retained velocity and energy.

For the shot criteria I used a 75 gr. bullet at 980 fps, which is 160 FPE of muzzle energy, and the rifle is sighted at 100 yards.... I then plotted Drop, Drift, Velocity and Energy vs. the BC, for four values of BC.... 0.05 (a typical pellet).... 0.10 (a large cal, low SD bullet).... 0.20 (a smaller cal, mid SD bullet).... and 0.40 (a small cal, high SD bullet, used for comparison purposes only).... Note that each BC is twice the previous one.... Here is what happens as you increase the BC....



Note that the biggest difference in drop is between pellets and bullets, and even that is not really significant until you push over 200 yards....



Wind drift is inversely proportional to the BC.... If you double the BC, you basically cut the wind drift in half....



The higher the BC, the less velocity is lost as the bullet goes downrange.... Once again, the difference between pellets and bullets is huge.... and BC becomes more important as range increases....



This is probably where BC makes the biggest difference.... Consider these comparisons, starting with a muzzle energy of 160 FPE (a 75 gr. bullet at 980 fps)....

If the BC is 0.40, the retained energy is 119 FPE at 400 yards....
If the BC is 0.30, the retained energy is 119 FPE at 300 yards....
If the BC is 0.20, the retained energy is 119 FPE at 200 yards....
If the BC is 0.10, the retained energy is 119 FPE at 100 yards....
If the BC is 0.05, the retained energy is 119 FPE at 50 yards....

There can be no doubt that bullets are far superior to pellets for reduced wind drift, retained velocity and retained energy, because they have roughly twice the BC.... If you double the BC again, because of careful selection of caliber and bullet design.... you can reap those gains again....

Bob

[Tofazfou]

Great visuals Bob.

This is why i've choosen the LBT 90 gr LFN to replace the Lyman 257420's in my particular gun.  With some very rough and limited range numbers, the LBT catches in FPS and passes the lyman at roughly 150 yards but surpasses it in FPE from them muzzle to infinity not just because of the weight but because of the BC.

[nielsenammo]

I have guns I shoot both pellets and slugs in and you can really tell the difference when you shoot in the wind.  The pellets move so much and the slugs still move around in the wind but noticeably less.  I like the flatter shooting they provide as well.  I like the graphs for a reference.

I still will take a more accurate slug over a higher BC slug all day long - we need to find the magic compromise that gives the best of both of these.  We can get it with custom guns and bullets made to shoot with each other but manufactures need to recognize that is what some of their customers want and make guns that shoot what we want to shoot.

[rsterne]

Agree 100%, accuracy is everything.... but if you can have both, then why not opt for the higher BC?.... For the most part, the BC is proportional to the SD, so for a given weight, and therefore FPE level (because we tend to shoot mostly in the 900s), this favours smaller calibers, with longer, thinner bullets.... Even if we keep the SD a constant, so that we are dealing with the same barrel length and pressure, the advantage still lies with the smaller caliber, but in that case the bullet weight and therefore FPE will decrease.... and the benefit is less air used as well....

Generally, how much FPE to you need to kill a Varmint?.... I can see the day coming, likely not far off, when we will have .224 cal rifles shooting 60-70 gr. Spitzers that will deliver all the power you need for varmints to 200 yards.... with pinpoint accuracy.... All it will take is the custom PCPs guys to realize not everyone wants a 500 FPE monster....

Bob