Long-range trade-off? Better BC, or more velocity?

T

tobnpr

New member
Where does the advantage lie?...
I've developed our most accurate loads at shorter range (200M) and we're now stretching out from 600 to 1000.

Just discussing generalities, not related to specific caliber.

Larger bullets have higher BC's, but obviously lower velocities.
Smaller bullets have lower BC's, but can be pushed faster.

I realize every rifle has it's own preferences...

But is there a fundamental rule of external ballistics that would favor one over the other, or is there no such rule, and it's just the usual trial and error method of load development?
 
Better BC at useful velocity.

To whit: In a .223 Remington, the 52gr match bullets can scream (3200-fps) while you're pretty well topped out around 2700-fps with an 80gr bullet (all 20" barrel speeds). But I assure you the 80 will shoot far, far better at 600 yards than the 52 will. Better BC, better flight.

Also, consider the 69, 75 and 77gr "magazine" bullets in .223. While these are better than the 52s out to 300-500 yards, they're still not quite to the class of the 80gr Matchkings or 75gr A-Maxs (or any of the true VLD bullets). You can push the 69s to 2800-2900 fps with a 20" barrel, while the 75-77s can again creep up to the 2700 mark with the right powder.

Sorry I'm not including the exact BCs for any of these bullets, but as I recall the 52s are under .3, the 69s are in the .33-35 and the 75/77s are around .37. The 80s are in the range of .42-45.
 
Most people only think of bullet drop when considering long range shooting, but the effect of wind is a lot more variable and a lot harder to dope than drop is. Velocity helps, but ballistic coefficient is the real tamer of wind drift. Go with the higher BC if shooting beyond 400 yards.
 
Velocity does not equal accuracy.

If you've got an accurate load for your rifle and you want to reach a bit farther, adjust your sights.
 
It's a combination of both since BC usually increases with the weight of the bullet but for the most part i'd rather run a higher BC bullet at 2600fps than a lower BC at 2850fps. Just my preference.

“Muzzle velocity is a depreciating asset, not unlike a new car, but BC, like diamonds, is forever.” - German Salaza
 
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Most people only think of bullet drop when considering long range shooting, but the effect of wind is a lot more variable and a lot harder to dope than drop is. Velocity helps, but ballistic coefficient is the real tamer of wind drift. Go with the higher BC if shooting beyond 400 yards.
Click to expand...

This is a valid point...
But playing Devil's advocate, the smaller, faster pill (with the lower BC) is going to get to the target faster, and so, wind has less time to affect trajectory.

Seems there is a (-) to every (+)...

So you feel this tradeoff goes to BC?
 
Yes by far retained velocity downrange (1000yds) is far more important than the initial velocity of a lighter projectile. Remaining supersonic and stable is again very important, as is bucking the wind.
 
There is no tradeoff. BC is most important, by a wide margin.

But playing Devil's advocate, the smaller, faster pill (with the lower BC) is going to get to the target faster, and so, wind has less time to affect trajectory.
Click to expand...

BC effects velocity retention as well, and the difference in flight time to the target is negligible. Running some numbers, for my rifle at my home range:

6.5-06,
.264 140AMAX @ 2818 FPS, 4400ft alt, BC .550

Velocity @ 300 2394 1.5MOA/10mpg F/V wind .34 sec flight time
Velocity @ 500 2130 2.5MOA/10mpg F/V wind .61 sec flight time
Velocity @ 1000 1551 6.3MOA/10mpg F/V wind 1.43 sec flight time
Subsonic @ 1575 yards

.264 95gr VMAX @ 3400FPS 4400ft alt, BC .365

Velocity @ 300 2692 1.9MOA/10mpg F/V wind .29sec flight time
Velocity @ 500 2273 3.4MOA/10mpg F/V wind .54sec flight time
Velocity @ 1000 1412 8.4MOA/10mpg F/V wind, 1.38sec flight time
Subsonic @ 1300 yards

The 140 load is my actual numbers for my long range rig. I have found them to be remarkably(surprisingly?) accurate.

The flight time difference to a 500 yard target is a whopping .07 of a second, and to 1000 is even less, .05 sec, as the 140 grain bullet is going faster at that point. The velocity is equal at about 725 yards. From that point on, the 140 grain bullet, that started 600 FPS slower, is traveling faster.

If your theory is correct, the lighter faster bullet should have less wind when it is traveling faster, but even then it comes up short, with .4MOA more wind at 300 yards, and .9 MOA more windage at 500, even though it is still traveling as much as 300 FPS faster.

In fact, if you set the table steps to 25 yards, you will see the lighter bullet has more windage from as close as 50 yards.
 
Most of my experience is with the '06. The 110-grain bullet starts off a bunch faster than the 180, but the 180 has a better trajectory for 500-yard shots. The 110 slows down more quickly: Poorer BC.
 
If I remember correctly, and maybe I don't, wind drift is proportional to the drop in velocity as opposed to the time of flight. So the faster bullet that loses velocity fast will drift more than one that holds its velocity better. That would indicate that the BC is the more critical of the two. I am not sure why that is true if it is, but I do remember reading that in some ballistics manual.

I am willing to be straightened out on this.

I suppose we could go to one of the ballistics program and crunch some numbers and find out.
This one might do it. http://huntingnut.com/index.php?name=PointBlank

Jerry
 
Emcon,

Thanks for running some numbers.
Looks like somewhere past 500 the higher BC bullet, because of superior velocity retention, passes the smaller pill. Even though the heavier bullet leaves the muzzle slower, the smaller pill loses it's velocity faster due to the lower BC.

Got it...
 
The velocity is equal at about 725 yards.

For a more extreme example, lets loot at 20 gr .172 VMAX from a 17 Remington, fired at 4300 FPS, and compare it to the same 6.5 140 AMAX above, but fired from a 6.5X50 Japanese at a relatively light loaded 2150 FPS.

Even though the little bullet has twice the muzzle velocity of the big one, it is only equal in the wind for 50 yards, with .4 MOA drift in a full value 10 MPH Wind. By the time it gets to 75 yards, the .17 is already up to .7 MOA drift, where the 6.5 is only .5 MOA.

The .17 also sheds about 500 FPS between the muzzle and 100 yards, the 6.5 loses only ~130FPS.

Again, this is an extreme example, the .264 140GR AMAX is a really good bullet ballisticly (BC .550), and the .17 is about as bad as a bullet gets with a BC of only .185, but it does show that now matter how fast you push it, velocity won't make up for crappy ballistics.
 
BC after 200 to 300 yards. Drop is a constant you set your scope up for the drop if you know the distance/velocity and it will always drop the same amount. Wind drift is changes and can change between the time you pull the trigger and when the bullet hits the target. Wind can be at the target yet not at the line or somewhere in the middle or different at all three.

2 other things to consider. The fastest load is not always the most accurate load and when shooting you have to stay above the transonic barrier or the bullet becomes unstable. The last usually only becomes important at 1000 and better for any cartridge used in LR
 
here is a comparison of a .204 shooting a Hornady Vmax at 4150 and a .308 shooting a Berger 155.5 at 2750. The 204 is a factory load using God knows what for powder , I cant get within 200FPS of that speed with handloads w/o pressure signs.The 308 data is my most accurate handload for that bullet, I could squeeze another 200FPS out but would sacrifice accuracy.

Notice that out to 400 yards (good varmint range for most of us) the wind drift difference is negligible. At 1000 though....



Code: 
+----------------------------- Program Inputs ---------------------------------+
|                                                                              |
+---- Bullet Inputs -----+----Atmosphere Inputs ----+-------Sight Inputs ------+
| Caliber: 0.308 inches  | Temperature:  59 degrees | Sight Height: 1.5 inches |
| Weight: 155.5 grains     | Pressure: 29.92 inHg     | Zero Range: 100 yards    |
| G7 BC: 0.464 lb/in^2   | Humidity:   0 %          | Look Angle:   0 degrees  |
| G7 Form Factor: 0.505  | Density: 0.07647 lb/ft^3 |                          |
| MZL Velocity:  2750 fps| Wind Speed: 10 mph       |                          |
|                        | Wind Direction: 3 O'clock|                          |
+------------------------+--------------------------+--------------------------+


+----------------------------- Program Output ---------------------------------+
       Range    Velocity    Energy     Trajectory         TOF          Drift
      (yards)     (fps)     (ft-lb)     (inches)         (sec)       (inches)
          0      2750        2611          -1.50         0.0000         0.00
        100      2650        2425           0.00         0.1111        -0.36
        200      2552        2249          -3.45         0.2264        -1.46
        300      2457        2084         -12.23         0.3462        -3.35
        400      2363        1928         -26.78         0.4707        -6.07
        500      2271        1781         -47.55         0.6002        -9.66
        600      2182        1643         -75.06         0.7350       -14.19
        700      2094        1514        -109.88         0.8753       -19.69
        800      2009        1393        -152.62         1.0216       -26.24
        900      1925        1279        -203.99         1.1741       -33.90
       1000      1843        1173        -264.73         1.3334       -42.73
Code: 
+----------------------------- Program Inputs ---------------------------------+
|                                                                              |
+---- Bullet Inputs -----+----Atmosphere Inputs ----+-------Sight Inputs ------+
| Caliber: 0.204 inches  | Temperature:  59 degrees | Sight Height: 1.5 inches |
| Weight:  32 grains     | Pressure: 29.92 inHg     | Zero Range: 100 yards    |
| G7 BC: 0.210 lb/in^2   | Humidity:   0 %          | Look Angle:   0 degrees  |
| G7 Form Factor: 0.523  | Density: 0.07647 lb/ft^3 |                          |
| MZL Velocity:  4150 fps| Wind Speed: 10 mph       |                          |
|                        | Wind Direction: 3 O'clock|                          |
+------------------------+--------------------------+--------------------------+


+----------------------------- Program Output ---------------------------------+
       Range    Velocity    Energy     Trajectory         TOF          Drift
      (yards)     (fps)     (ft-lb)     (inches)         (sec)       (inches)
          0      4150        1224          -1.50         0.0000         0.00
        100      3898        1079          -0.00         0.0746        -0.41
        200      3649         946          -0.79         0.1541        -1.69
        300      3404         823          -4.20         0.2392        -3.95
        400      3164         711         -10.61         0.3307        -7.32
        500      2930         610         -20.51         0.4292       -11.94
        600      2705         520         -34.46         0.5357       -17.97
        700      2489         440         -53.17         0.6513       -25.60
        800      2283         370         -77.51         0.7772       -35.03
        900      2087         310        -108.53         0.9146       -46.50
       1000      1901         257        -147.56         1.0652       -60.29
 
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