BC difference? How much does it matter?

[Ketosan]

Had a discussion with a friend about just how much does it matter when you start comparing BC numbers?? For example: a Hornady ELD-M 208 Gr bullet has a G-7 of .348 and a Hornady ELD-X 212 Gr has a G-7 of .334. Is this difference something to take into account? and if so is there a % improvement with an increasing G-7 number? In the example above is the .014 increase in BC significant? Now I realize these are two different bullets--one match and one hunting but the question is more about just how much does BC matter?
My discussion friend in this matter seemed to think that the BC numbers where extremely important and he would place emphasis on that when selecting a bullet. My thoughts were they were important only to the extent that one produced tight consistent groups with a given bullet/load combination.
Just looking for everyone's thoughts on this--I'm sure there is no right or wrong answer--

 

[CharlieNC]

The best way to address your specific case is to run the cases through a ballistic calculator at the velocities you expect, and the distance/wind conditions you expect to encounter. It will compute the results which you can decide if are significant or not. Especially wind effect.

 

[Ned Ludd]

You can see the difference in elevation required to hit a specific POA at 300 yd for bullets with G7 BCs that differ by as little as 2-3%. This difference is within the range of what you'd expect between unpointed and pointed bullets. However, depending on the type of shooting, small differences in elevation adjustment may not mean very much in practical terms. The main reason most shooters want increased BC is the increase in resistance to wind deflection that goes along with it, not the decrease in elevation adjustment, although there may be an exception for some that want the "flattest" trajectory possible for a given cartridge.

The easiest way to determine whether a difference in BC will be meaningful to you is to actually plug the two BCs into a ballistics calculator such as JBM. Using your specific setup values (MV, distance, etc.), you can see whether the difference in wind deflection between the two in a full value 10 mph wind at some specified distance is large enough that you can reliably shoot the difference. If "yes", the higher BC bullet might be worth consideration. If "No", you're not going to gain anything by switching. In general, if I can't see at least 0.1 MOA difference at 600 yds, I cannot reliably shoot the difference. Using the same procedure, you can easily back-calculate how much the difference in the BCs of two bullets needs to be to generate a specified difference in wind resistance at a specified distance. Typically, I think you'd need at least a 2-3% increase in G7 BC to be meaningful and an increase of that magnitude might only net you an extra point or two in a match every now and then. In other words, not a huge difference and rather difficult to prove the effect beyond a shadow of a doubt. If the difference goes up to 5-10%, then the gains will be more noticeable.

The final caveat to all this that the higher BC bullet must be able to be loaded in your setup so that it shoots with at least the same degree of precision as the lower BC bullet. A high BC bullet in a load that shoots with poor precision is counter-productive.

 

[Scott Harris]

...the higher BC bullet must be able to be loaded in your setup so that it shoots with at least the same degree of precision as the lower BC bullet. A high BC bullet in a load that shoots with poor precision is counter-productive.

^^^THIS^^^

BC is nice, shooting small is essential.

 

[Ledd Slinger]

Without considering accuracy, which isn't even the subject anyhow, BC isn't as significant as most people would think.

It's all relative to how far you want to shoot. One thing a lot of folks don't remember is that a lighter bullet with a much lower BC can travel with a trajectory that matches or even drops less than a heavier bullet with a much higher BC out to a certain distance. Why? Speed.

Trajectory has everything to do with maintained velocity over distances. A heavy high BC bullet will not drop less than a light lower BC bullet until it reaches a range where it's lesser rate of speed loss overcomes the initial disadvantage in trajectory it had at the shorter ranges. The lighter bullet gets to shorter ranges much quicker with less drop, then begins to plummet faster at longer ranges. The heavier bullet dropped more at shorter ranges and has to make up the drop deficit it initially had with the lighter faster bullet over a long distance before it exhibits a flatter trajectory from there on out.

Case in point, if you were to take a 7mm Berger 168gr VLD (G7 .316) and launch it from a 7mm Rem Mag at 3000 fps, then take a 7mm Berger 140gr VLD (G7 .256) and launch it from the same rifle at 3200 fps, the larger higher BC 168gr VLD would not begin to show a less drop until it reached about 800 yards.

That is a G7 BC difference of .060, yet the larger bullet does not drop less until after 800 yards. Until then, the much lower BC bullet has less drop in its trajectory.

 

[284winner]

BC is certainly a factor but not typically until beyond 500 yards in most cartridges we see used for long range work. Obviously putting a 45/70 up against any shouldered cartridge, BC will have a tremendous amount of consideration. Typically it wont until many football fields down range.

 

[DocUSMCRetired]

Elevation is easy to account for. Wind can take much more skill to manage. Higher BC = Less Wind Effect.

But some good points were brought up, you need to be able to load and shoot them reliably in your system. Also if range, or lack of knowing the range (varmint hunting comes to mind) is unknown. A flatter trajectory can be beneficial.

 

[SheepDog]

Wind effect is still time dependent. The faster a bullet gets to a given range the less time the wind has to move it.
The common denominator in drop and drift is time.

 

[Mr.Knowit all]

Had a discussion with a friend about just how much does it matter when you start comparing BC numbers?? For example: a Hornady ELD-M 208 Gr bullet has a G-7 of .348 and a Hornady ELD-X 212 Gr has a G-7 of .334. Is this difference something to take into account? and if so is there a % improvement with an increasing G-7 number? In the example above is the .014 increase in BC significant? Now I realize these are two different bullets--one match and one hunting but the question is more about just how much does BC matter?
My discussion friend in this matter seemed to think that the BC numbers where extremely important and he would place emphasis on that when selecting a bullet. My thoughts were they were important only to the extent that one produced tight consistent groups with a given bullet/load combination.
Just looking for everyone's thoughts on this--I'm sure there is no right or wrong answer--

I agree with you completely What good is a ultra-high BC bullet if it won't group for shit??? At least for the type of shooting I do.

I think some of you/us are getting of track. My question basically is (to the few that went of on a tangent) how much will you be off using a G1 BC on a G7 bullet?

Thanks Doc for the links you posted and to all you guys for taking the time.

 

[284winner]

I agree with you completely What good is a ultra-high BC bullet if it won't group for shit??? At least for the type of shooting I do.

I think some of you/us are getting of track. My question basically is (to the few that went of on a tangent) how much will you be off using a G1 BC on a G7 bullet?

Thanks Doc for the links you posted and to all you guys for taking the time.

Yes you make a great point. That really WASN'T the question was it ? This question is beyond my knowledge level. I know conversion for G1 to G7 but it's pretty much irrelevant to me. I simply use one form and stick with it. It's been working fine for me. This is where you will find the answer tho.

 

[JPeelen]

No global number exists that can tell us how much the result will be off when using G1 instead of G7. Both curves have different shapes and the difference between them varies continuously with velocity.
An example: Lapua .224 S538 (BC 0.251 G1) bullet with 3133 fps muzzle velocity:
At 300 m G1 will show 1985 fps remaining velocity, while in reality it is only 1907 fps.

But any other bullet (different velocity, different air drag, different sectional density) will show other numbers.

 

[IdahoSharpshooter]

G7 BC is like diamonds
MV is like coasting on a level surface. You get an initial push, then immediately begin slowing down.

 

[Derrick]

Some of us get hung up on one particular part, me included. I once though only the high BC bullets are going to be more accurate. With that said, as mentioned above, wind and distance, is what I would be concerned with. If you shoot long distance the majority of the time I would run the higher BC projectile. If you are trying to produce the smallest group size at 100 yards, I would shoot a projectile that matched the twist of the rifle. NOW With heavier projectiles should come with higher BC's, the projectiles you mentioned above, the heavier one has less G7 BC so I would go with the lighter bullet with the higher BC's. Then again you should input your MV into a ballistics calculator and see what you would gain. I hope this helps. I know my explanation was not the best.