Help understanding bullet BC

[CBB1]

So I was looking at bullet BCs today and I noticed that Hornady shows the exact same G1 and G7 numbers for the 6mm 108gr ELDM as the .270 143gr ELDX. Can someone explain to me why the 108 is so highly thought of and the 270 is made out to be a bowling ball?


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[Wrench]

Bc is simply a bullet's drag resistance. It is not caliber specific.

 

[Macintosh]

If Im understanding the question, its more “why does everyone talk trash about the 270 for longer range when this bullet option has the same BC as everyone’s LR sweetheart the 6cm”?

 

[CBB1]

If Im understanding the question, its more “why does everyone talk trash about the 270 for longer range when this bullet option has the same BC as everyone’s LR sweetheart the 6cm”?

That’s a better way of putting it. I just bought a 1:8 243 to shoot the 108eldm. Is less recoil the only thing I’m gaining by not sticking with my 270? Assuming I’m moving them at roughly the same MV.


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[hereinaz]

Because the 143 is not really the bullets they are talking about. Isn’t it relatively new?

Loaded ammo for the .270 under factory SAAMI specs is what gets “bashed” as low BC.

 

[hereinaz]

That’s a better way of putting it. I just bought a 1:8 243 to shoot the 108eldm. Is less recoil the only thing I’m gaining by not sticking with my 270? Assuming I’m moving them at roughly the same MV.


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Less recoil and some case efficiency/precision are gained.

You lose some wind drift with the 6cm smaller bullet.

 

[Wrench]

The 270 win wasn't twisted hard enough to take advantage of the truly magical bc bullets.


Yet still remains a legend.

 

[CBB1]

Correction, it is the 145 eldx


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[CBB1]

Any more clarification on this would be greatly appreciated.


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[Formidilosus]

Any more clarification on this would be greatly appreciated.


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The 145gr ELD-X is probably the best bullet on the market for standard 270win. However to match a lowly 6mm or 243 you need 20 more grains of powder, and right at double the recoil. For what?
Another way to look at it, is for the same recoil of a 270 win/145gr ELD-X, you can shoot a 6.5 PRC with a 140gr or 147gr and be measuravly better in wind drift and external ballistics.


The 270 is cool, and if someone has one and wants to use it the 145gr ELD-X is the choice. But to start over with a new rifle in 270, yeah no.

 

[CBB1]

Thank you Form, that clarifies things. Cartridge efficiency is the difference. I’m working my way into the smaller, more efficient cartridges but I have a couple of 270s that are hard to let go of.


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[bnewt3]

Im assuming you are talking about a modern 6mm not 243. I would bet because both 243 and 270 were designed with relatively short bullets, and both of those bullets in question are longer than typical, they will both eat into case capacity and you will get similar reduction in velocity.......where the modern 6mm are designed with the longer bullets from the beginning.

 

[blkqi]

Your original question is conflating a .270 bullet with the the .270 Winchester cartridge.

Give any of those Winchester cartridges a fast twist and long throat and they will absolutely hang with modern long range cartridge designs.

 

[bnewt3]

To further illustrate @blkqi point
270WSM
vs
6.8 Western

both CAN be loaded with the same high BC bullets but the 270WSM case was not designed for it so you eat up case capacity with the longer bullet losing velocity and trajectory. along with 270WSM never came in a factory rifle with a twist rate to properly stabilize the long-for-caliber bullets.

 

[CBB1]

I guess I don’t understand it enough to clearly ask the question. But looking at 2 different caliber bullets of different weights that have the exact same BC listed on the box, why is it the 243/6mm 108gr bullet is loved and not the 145gr 270/6.8 bullet.

The way I think I understand it now is that you have to pay the price of recoil to achieve the same results. Only other question, what terminal difference does the additional 37 grains of bullet weigh make. Based on what Form has said on the S2H podcast maybe a couple inches in wound channel diameter?


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[bnewt3]

Idk the answer to that.
I personally don't subscribe to this "let's see how small a bullet we can use to take the biggest game possible" game people are playing these days.

That being said making game die as quick as possible should be the point and dead is dead.

 

[Shortschaf]

why is it the 243/6mm 108gr bullet is loved and not the 145gr 270/6.8 bullet.

It probably IS loved by those who shoot .270cal

Maybe you see disparity because for every 1 person that shoot's .270cal there are 100 people who shoot a 6mm, 100 that shoot 6.5mm, and 100 that shoot 30cal

 

[wind gypsy]

Your original question is conflating a .270 bullet with the the .270 Winchester cartridge.

Give any of those Winchester cartridges a fast twist and long throat and they will absolutely hang with modern long range cartridge designs.

Hang with to the point that most all of us won’t be able to detect any difference, I agree. Still, even the limited heavy for caliber bullet options in 277 are inferior on paper compared to 264 and 277 options so they are a less attractive option IMO.

 

[z987k]

So I was looking at bullet BCs today and I noticed that Hornady shows the exact same G1 and G7 numbers for the 6mm 108gr ELDM as the .270 143gr ELDX. Can someone explain to me why the 108 is so highly thought of and the 270 is made out to be a bowling ball?


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Almost entirely recoil. If you have the exact same muzzle velocity, then their trajectories will be identical.

 

[bnewt3]

One extremely minor detail is the sectional density of each.
.261 for the .243
.2699 for the .277

So assuming they hit at the exact same velocity, the .277 will penetrate a bit deeper.