BC. How important is it?

Don't be concerned that you only have VV powders.
After lots of experimentation with powder choices, I have found that N140 turned out to be the most accurate powder for my two latest .308s with 150, 155, 168, 175, 190 and 200 grain bullets. I have tried Sierra, Berger, and Nosler bullets.

Also, don't conclude anything before you shoot the particular bullet in your particular rifle. The bullet shape, especially how much of the bullet is actually touching the rifling, has a lot to do with how your particular rifle performs with that bullet. BC matters after the bullet is out of the barrel, but only if the rifle likes the bullet shape and weight to start with.

My two .308 rifles are both Savages - they shoot better than I can but they have preferences for bullets, even bullets with the same weights.

One Savage has its best overall average with 175 SMK bullets then with 200, 150 and 190 SMKs all averages for all loads shot for each weight are with N140 powder and are at or under 0.48 inches. The best load for the 175s is 0.295 inches at 100 yards.

The other Savage has its best overall average with 155 Bergers and then 155 Noslers followed by 175 Noslers followed by 150 and 190 SMKs - also all with N140 powder. However, all of its top 5 averages are under 0.456 inches with the best load a 0.296 with the 155 Bergers. This Savage actually shoots slightly better on average than the first one but not with the same bullets.

You will have to determine what your barrel shoots most accurately if you are looking for accuracy alone. However, from a long range shooting perspective, you will probably find that what works really well at 100 yards may work out to 300 yards but may not hold up when you move out to 600 yards and more.

In addition to finding out that technique is crucial when you shoot at longer ranges, you might find that there is a big trade off between initial shorter range accuracy and longer range stability with the added factor of being able to read the wind. BC helps but as Bart said, the bullet can't find its way back onto the target at longer ranges if it initially strays off the intended path.

Bart is a much better source of knowledge on the long range technique part of the equation than I will ever be.
 
I mostly agree with the other posters. 308 is capable of 1000yds but there are better choices. Since the OP is a question about BC I'm a little surprised that no one has mentioned 7mm bullets. I have been trying to reach out to longer distances with my 308, and it's got me looking around for a 7mm Mag. The BC on those 7mn bullets is way above anything comparable in 30 cal (unless your interested in lobbing 210gr++ bullets downrange). IIRC a 308 175gr SMK has a BC of .502. A 7mm 175gr SMK has a BC of over .6!!
 
BC has some import, but not as much as matching the bullet, OAL, velocity to your barrel. Also, realize that some bullet manufacturer's are a bit optimistic about the BC they publish. The BC is actually variable (slightly) based on many parameters. When I have shot onto ballistics cards from 100m to 300m, I found that the BCs, for that given set of conditions could vary by as much as 0.04 from the published numbers, but usually no more than 0.015 or so.

When a bullet leaves the barrel, for some length, it is flying supersonically backwards. The gases accelerate around the slug and at some point (5 to 10 feet out) the bullet breaks the sound barrier as it surpasses the speed of the gases by the local speed of sound (why comps and suppressors "can" increase accuracy and change POI). Then you have nutation to worry about, and then somewhere downrange, the bullet goes trans-sonic again. Lighter bullets, based some on the SD and the spin rate, tend to be disrupted more due to crossing the sound barrier (both times), than heavier bullets. While there are a lot of variables with an effect, in reality, that is the biggest reason that the heavier bullets, if properly stabilized, are more accurate at range. If you do the math, a light bullet fast has a worse BC, but less time in the wind while a heavy bullet slow has more time in the wind. In most cases, if your ballistics calculations properly account for atmospheric, twist rate, changing BCs, etc. it is a wash inside the 2nd trans-sonic point.

Due to nutation, the average trajectory is kind of the shape of a coke bottle. The cone opens to a point, but then when the bullet has settled, basically you have a cylinder for a period of time, and then it reverts back to a slowly opening cone and then at the 2nd trans-sonic, a quickly opening cone.

All that said, the .308 is fine out to about 1000m, but, you will find some less expensive bullets that are just as accurate out to about 600m. I would never pick a bullet solely based on BC. I pick a bullet weight and work a few powders and bullets around my target velocity. Once I find one that works okay and call it a midpoint, then I start to vary crimp, OAL and 0.1 grain variations until I get the best I can out of that rifle for that barrel. Switch barrels, I go back to that midpoint and work back up from there. I tend to steer folks towards 155 Palmas at about 2700 fps to work on their technique and increasing range. Depending on how good you want to be, and/or how much you can get to the range, you could very well be halfway through the barrel life shooting 155s before you even need to really consider heavies and moving out to or past 1000m. Just realize, you want to keep tabs in your notebook on that "midpoint" load and maybe every 500 rounds, shoot a group at 300m. This should keep you centered in reality, help you track your improvement and most importantly, let you know when the rebarrel is due (or check your crown, change your cleaning procedures, etc.).
 
It is important, however it is not the end of the world if the bullet you are using is not the best BC available. I ran some numbers, using your 155 AMAX, and since I had the Hornady manual handy, a couple other flavors of .308 AMAX.

Listed it the calculated drift for each bullet at a few ranges:

155 AMAX @ 2600 FPS. BC 0.435 G1 (subsonic @ ~950 yds at sea level)
10mph full value wind
300 yds: 8.4 inches, 2.7 MOA
500 yds: 25.4 inches, 4.9 MOA
700 yds: 54.7 inches, 7.5 MOA
1000 yds: 125 inches, 12 MOA

178 AMAX @ 2400 FPS .495 G1 (subsonic @ ~975 yds at sea level)
10mph full value wind
300 yds: 8.2 inches, 2.6 MOA
500 yds: 24.5 inches, 4.7 MOA
700 yds: 52 inches, 7.1 MOA
1000 yds: 117.1 inches, 11.2 MOA

208 AMAX @ 2300 FPS .648 G1 (subsonic @ ~1200 yds at sea level)
10mph full value wind
300 yds: 6.5 inches, 2.1 MOA
500 yds: 19.1 inches, 3.6 MOA
700 yds: 39.7 inches, 5.4 MOA
1000 yds: 88.1 inches, 8.4 MOA

Frankly, I am surprised how good the 155 is compared to the 178. I expected the difference to be greater.

In reality though, if you call the wind correctly, BC does not matter, provided the bullet is supersonic all the way to the target. If you call teh wind perfectly and adjust accordingly, the result is the same, a hit.

When it does help greatly is when you get the wind call wrong. For example, if you call 10 MPH @ 90º and the real value is 7 mph @ 75º, how bad will you miss?

This is how far your bullet will land from where you think it should go based on the wind call, using the same velocities and environment as above.

155 AMAX
500 yards, 8.2"
1000 yards 40.5"

178 AMAX
500 yards, 7.9"
1000 yards 38.1"

208 AMAX,
500 yards, 6.2"
1000 yards 28.7"

If it was me, I would figure out a load that works in my gun and is supersonic as far as I wanted to shoot, and call it good.
 
If you fix all the variables and only change the BC then it will give us a feel for how much of an effect the BC has.

Value:
Zero distance: 5 yards
Sight height: 0 inches
Muzzle Velocity: 2000 FPS

This is basically thinking of a rifle as a cannon, or shooting down the barrel and not down the sights.

Time of Flight in Seconds = TOF

BC = 0.1
100 Yards: TOF: 0.18, Vertical: -5.6", Velocity: 1336
200 Yards: TOF: 0.45, Vertical: -31.0", Velocity: 1014
500 Yards: TOF: 1.59, Vertical: -368.9", Velocity: 624

BC = 0.25
100 Yards: TOF: 0.16, Vertical: -4.6", Velocity: 1705
200 Yards: TOF: 0.35, Vertical: -21.3", Velocity: 1446
500 Yards: TOF: 1.12, Vertical: -195.5", Velocity: 1014


BC = 0.5
100 Yards: TOF: 0.16, Vertical: -4.4", Velocity: 1775
200 Yards: TOF: 0.33, Vertical: -18.9", Velocity: 1705
500 Yards: TOF: 0.92, Vertical: -143.4", Velocity: 1336

These are G1 ballistics that I calculated with my Gun Log SPC app on my iPhone. I wrote the calculator myself.

The BC is all about drag, the slowing down in the atmosphere. The slower a projectile goes, the longer it takes to travel a given distance, and since it takes longer it has more time to fall and therefore it drops more.

BC is important.
 
If it was me, I would figure out a load that works in my gun and is supersonic as far as I wanted to shoot, and call it good.
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Then I think I need to eventually move on to N540, N550 or the like.

I will need the extra oomph to keep any bullet I choose/can find supersonic for 1000m!! With the latter a 155gr Scenar would have a muzzle velocity of 2950fps according to Lapua (test barrel, twist all the same as mine)...

Very interesting numbers though: thanks for taking the time.

If I take a step back, I think that due to my early (very early) success, or degree there of, with my OCW charge investigations, I've started finding what my rifle can do and it seems like it could do a lot for me. This means that I am now looking to what can bring me closer to my 1km goal. As another member said, beware of running before walking.

I still want to explore all these options, but the apparent time and upfront money investment for bullets and powders, I may put the brakes on a bit and stick to the 155s for now, although I want to explore the Scenar 155 HPBTs.

It may turn out that I don't need to go much further. It certainly seems the mid-weights are not the best, taking those figures as examples.
 
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Furthermore, your rifle, sight height, and zero distance would be a fixed, a constant, a value that doesn't change between loads.

What does change is the BC and the Muzzle Velocity. Those two factors will make the difference on bullet drop.

Energy is effected by bullet weight, so if you wanted a certain impact energy at a certain distance then you would have to work with bullet weight, muzzle velocity, and BC.
 
Can you run that calc again for say 0.45 to compare to the 0.5? The would give the OP a better understanding of picking one or the other just based on BC. :)

I don't even shoot pistol bullet with a .1 BC and most of the choices in a given caliber and weight vary by maybe .05 or so.
 
sirgilligan said:
Those two factors will make the difference on bullet drop.
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I am not disagreeing with you, but need to point out that drop is not important in fixed range LR shooting, provided your sighting system has enough elevation adjustment to get on target.

As long as the sights can get you there, it really doesn't matter that the 155 AMAX takes ~42 MOA to get on target at 1000 yards and the 208 AMAX takes ~41. All that matters is the wind.

It is interesting to note though, and a good example of the importance of BC. The ~25% heavier bullet starts 300 FPS slower, yet arrives at 1000 yards faster (1.800 vs 1.859 sec flight time) with more velocity and less drop.
 
BC. How important is it?
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Very.

If you want to see how dramatic BC can affect ballistics take a look at shotgun pellets or .22LR projectiles versus .338 whisper.
Most shotgun pellets start at a velocity over or around 1300fps. And .22LR usually has a MV in the 1050-1300fps range. While a .338 whisper will fire a 300 grain bullet at around 1050fps.

.338 whisper would be able to shoot over 500m
A shotgun load or .22LR would not even be close to that. Good luck getting anything on paper. The wind is going to have a field day with those low BC projectiles and they're going to lose a ton more velocity.
It takes about 200 yards for a high BC 300 grain .338 bullet to lose 50fps from the initial 1050fps MV. It takes about 20-30 yards for a 40 grain .22LR bullet fired at 1050fps to lose that same 50FPS.
 
Can you run that calc again for say 0.45 to compare to the 0.5? The would give the OP a better understanding of picking one or the other just based on BC.
Click to expand...

Again, zero at 5 yards, sight height at 0.0", muzzle velocity of 2000 fps.

BC 0.45
100 Yards: TOF: 0.16, Vertical: -4.4", Velocity: 1832
200 Yards: TOF: 0.33, Vertical: -19.2", Velocity: 1675
500 Yards: TOF: 0.95, Vertical: -148.5", Velocity: 1282

BC 0.5
100 Yards: TOF: 0.16, Vertical: -4.4", Velocity: 1848
200 Yards: TOF: 0.33, Vertical: -18.9", Velocity: 1705
500 Yards: TOF: 0.92, Vertical: -143.4", Velocity: 1336

p.s. Remember that ballistic drag is not linear. A projectile might be slowing at rate "X" at one instance and then "7/10ths of X" at another instance. That is a reason it is tricky to estimate the flight of a projectile.
 
I am not a long range shooter. I do not play one on TV either.

I would think that the things that matter are:
  • A setup that is accurate. That means a rifle and load that are tuned to work together.
  • A scope that can show you the target and have enough adjustment for windage and elevation.
  • An accurate measurement of the wind and its actual direction. Remember that wind can move in all three dimensions, it is not just horizontal.

This is beyond my research into the topic, but I am pretty sure the rotational direction of the bullet effects the amount of wind push (deflection) if the wind is hitting the bullet directly in the side from the right side or the left.

A bullet rotating clockwise with a wind from the right would be biting down on the air and the same rotating bullet with a wind from the left would be biting up on the air. Too many variables for my brain to think of right now.

Then there is the rotation of the earth and so many other factors.
 
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Silly question, and possibly obvious, but:

Are you planning to hunt animals, or merely paper targets, at long range? Because that will constrain your ultimate choice of projectile.

I would buy and read Bryan Litz's books on long-range shooting, preferably several times, regardless of which it's going to be. (You can get them from his website, as I did; if you ask, I think he even signs them for you if that's what floats your boat.) Not to say that he is the all-knowing infallible God-King of Long Range, or that his writings and conclusions are applicable to everyone, but it does give one a perspective and a base to work from.

If all you plan to hunt is paper targets, you have at least eliminated two important factors - the amount of ENERGY with which the bullet must arrive and the behaviour of that bullet when it strikes a solid object. If you're planning long-range big game hunting, the requirements suddenly become a lot more demanding and BC has to take a back seat to terminal performance considerations.
 
Paper.

I don't hunt, but if I did I certainly would not shoot an animal at that distance.

If I do end up hunting I don't think I would shoot beyond 200m. In any case Estonia is very flat and heavily forested so the terrain and environment do not allow for hunting over much greater ranges.
 
I don't think the extra dough spent on high BC, VLD's is worth the dough for you.

JMHO, but my own experience is that inside 500-600 meters is not much more difficult than shooting at 100 or two...

You can't practice long-range wind calls at a couple of hundred meters. You need to actually be there doing it, at long-range. The bullet's still humming along at 500, affected by external influences but still mostly a "dial and press" deal.

As long as you've got the basics of form, trigger control and breathing down pat you'll hit consistently. It's beyond 500-600 or so that the wind really starts to move that bullet not just sideways, but up/down as well- and you won't get that knowledge from a ballistic computer.

No point wasting money on bullets where you'll never realize their potential at the range you're shooting. Load development often takes but a couple of trips to the range unless the rifle's really finicky.
 
tobnpr said:
You can't practice long-range wind calls at a couple of hundred meters. You need to actually be there doing it, at long-range. The bullet's still humming along at 500, affected by external influences but still mostly a "dial and press" deal.
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Well, you can't, but you can.

At sea level, a 22LR Federal 40gr Match bullet at 1080 FPS in a 10 MPH full value wind has about 3.9 MOA of wind at 100 yards, which is roughly the same as my 6.5-06 Long Range rig at 625 yards (140AMAX @ 2818 FPS). At 200 yards it has about 9 min, which matches my 6.5 at about 1200 yards.

To compare it to his .308 with 155AMAX, the 22LR at 100 has as much wind as his .308 at about 420 yards. At 200, it is roughly equal to his .308 at 800 Yards.

So you can't practice reading the wind with your .308, but you can practice.

On edit:

tobnpr said:
and you won't get that knowledge from a ballistic computer.
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Truth. Trigger time, trigger time, trigger time. Preferably with good coaching.
 
Mr. Pond,

I must remark, before I comment, your contribution to this forum, helps me realize how fortunate we are, us Americans to realize the liberties we do. The costs of material, and the regulations you are required to adhere to, makes your effort to this pastime most impressive.

A high ballistic coefficient is great, but at the range your limited to , it's really insignificant. The prices you quote for bullets and powder would make me consider, doing the best I could at the range you're limited to.

Flat based bullets are easier to manufacture precisely. 100yd benchrest shooters don't use BT bullets. They use flat based bullets because they are more consistent and they are less expensive.

Have you considered that the same skills that you apply to improve ability will apply at 1000yds, as well as 300yds. If you master the lower B.C. bullet, you might easier master the end bullet, at range. The most important factor is the shooter.

What I'm really getting at here, I wouldn't buy VLD type bullets for shooting at your range.

The differences in B.C. between bullets can be calculated for and compensated for enough, to get your first few rounds in sight, when you do get to shoot at long range. The rest is just fine tuning.
 
Flat based bullets are easier to manufacture precisely. 100yd benchrest shooters don't use BT bullets. They use flat based bullets because they are more consistent and they are less expensive.

Have you considered that the same skills that you apply to improve ability will apply at 1000yds, as well as 300yds. If you master the lower B.C. bullet, you might easier master the end bullet, at range. The most important factor is the shooter.
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First of all, thank you for confirming what my wife has long maintained: I've completely lost touch with reality when it comes to spending on my hobbies. If I'm wearing the same tired looking T-shirts 15 years from now, you'll all know why!!

Meanwhile, you raise a good point about flat base bullets. On the one hand I want to develop my ultimate LR load now and use it regardless of the distance, making me very familiar with its performance. However, you are right. If the 155gr Amax is €35 per hundred, the 150gr FMJFB is only €25.

I could no doubt get cheaper-than-Scenar Lapuas (€34 per 100 as opposed to €46) too or even PRVI (also €25/100).
If the 100-300 range is really not that demanding on the .30 calibre, then I could well practice with those. Being utterly broke after the Christmas break I at least have time to mull over my next purchase.

I think I will, nonetheless, explore the 155gr Scenar bullet as I have some already loaded up that I could incorporate into an OCW string, and others I could pull to reload at the missing string charge weights.
 
I am not sure of your goal, whether you want to develop the most accurate load or to do accurate shooting.

But consider barrel life. I am sure Bart can say more on the subject than I know. But every shot fired in an OCW string is a shot not fired for record.
 
Given the choice of a bullet with a .550 BC that produces 1 MOA accuracy at 1000 yards and 9" drift per mph of cross wind or a bullet with a .500 BC that produces .75 MOA accuracy at 1000 and 10" drift per mph of cross wind, I'll pick the lower BC bullet with better accuracy. Shooting 10 shots with a 2 MPH spread in cross wind will produce a smaller group at 1000 with the lower BC bullet shooting more accurate.

You can practice reading the wind with any cartridge. Those with more drift per mph of cross wind makes it easier; you can see the effects of subtle changes in wind speed a lot quicker.
 
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