That's not what I'm reading.

Still the case. Same weight, higher BC = moving faster down range = penetrates better.

That's the way I'm seeing what Derrick is saying. And I'm on the same page with him.

Yes I am actually saying both, don't think you can have one without the other, but I did a bad job of explaining it at 10 AM before church...

So BC is essentially equal to Sectional Density/Coefficient of form. Representing the projectiles ability to overcome resistance, which dictates its ability to maintain muzzle velocity and affects penetration.

Sectional Density is essentially the mass of a projectile/the cross sectional area. You are correct in saying that this is typically used in terminal ballistics to derive penetration. However unless I am missing something when you look at BC compared to SD as SD increases so does BC.

So what I was saying is if you have a 7 mag bullet that is 180 grains and a 30 caliber bullet that is 180 grains. The 7 mag bullet is going to have a higher BC therefore will reach the target with more velocity. Thus more energy. Bullets being equal, more penetration, given they are both launched at the same speed.


I am not a ballistition so let me know if I a wrong

You're right.

It really depends on other stuff. Bullets tend to open up more quickly at higher impact velocities which in turn can actually diminish penetration. You might get better penetration with something like a Ballistic Tip if you slow it down from 3100 fps to 2700 fps, for instance.

My point is that upon impact, the original BC of the bullet is moot, for obvious reasons. Penetration then becomes a question of velocity, which is changing, and sectional density which is also changing because the bullet's frontal diameter is changing.

But Diminishing penetration = Energy transfer and that brings us back to bang flop... which I like thats why I like the set type bullets, to me its not 100% about penetration its about energy transfer. Your "other stuff" really explains it actually there are a ton of factors, easiest to compare on a market level is BC.

All depends on what the bullet is designed to do at a range of impact velocities. BC can extended that range of the impact velocities

Best penetrating bullet just means you poke a hole. Right impact velocity, with right SD combined with a bullet designed for that impact velocity means you blew a hole right through....big difference.

I have a creedmoor but have only killed a few piggies so far. So cant comment on its on game performance

What you said is "All things equal a higher BC will penetrate better than a low BC bullet of the same weight, just like it cuts wind."

What I said is BC has nothing to do with penetration (outside of its effect on impact velocity as JG astutely pointed out) and I have explained why.

Here we go on the physics discussion again.

Yes, once projectile impacts target, BC is out the window. However, itis arriving with "x" velocity. Penetration necomes a question of velocity, yep, same as I see it. I look at it like the 2" x 4" traveling at 20 mph hitting the power pole, 2" x 4" bounces off, power pole wins. Move the 2" x 4" at 200 mph, then what happens?

Could I force a .45 cal expanded hollow point, from a 45-70, through an elk at 50 yards better than I could 300 yards? Well at 300 it has lost much velocity. Say it expands the same for conversation sake, at what distance is the same bullet carrying more velocity and therefore more energy delivery? 50 yards of course. Same illustration holds true for streamlined bullets. Higher BC yields higher velocity at distance, yields more energy delivery. But maybe I'm relying on hydrostatic shock more than contact, projectile trauma.

That's the way I see it... The deer I have shot at 700 yards with the Same bullet flip is using felt the same way... Bang flop

bc and sd used as a reference to determine penetration is moot and irrelevant.
a 45-70 will out penetrate just about anything on the planet and has poor bc and poor velocity, just saying. it does however have high sd
to many variables, bullet design, impact velocites, sd, bullet weight, all play a part.

Can't go with ya on that.

That is awesome

Interesting statement because you did not define a distance.at 100 yards yeah at 500 yards no..
At 200 yards the 6.5 creedmoor has over twice the energy, just run the Calculator on it A bc of .175 compared to .489 is a big difference

Impact depth, IE Penetration is derived from the formula Impact distance = Projectile length x (Density of Bullet/Density of target). That formula assumes that the velocity of the bullet is met with equal velocity of the target.

That being said run those formulas and I think you would be surprised that sectional density (density of the bullet) and BC or profile/ Length of projectile both do effect penetration

Where did you get that formula?

bc has nothing to do with penetration, sd i can agree. arguing bc does because of higher velocities down range is misleading, i can over come that with sheer velocity. a 220 swift aint gonna outpenetrate the 6.5 and its because of sd not bc. i can overcome sd with bullet design as well.
media being penetrated also plays a part. 220 swift will penetrate steel where the 6.5 cannot. to many variables.

thats newtons formula for impact depth

Okay. So now show me where BC exists as a factor in the formula.

Not so true...
BC uses mass/ SD in the formula so it does matter. Look at your swift argument

220 swift with a 55 grain bullet at 3680 vs my 22 creed shooting 75 grain amax at 3350.

at 400 yards, Both have a drop of about 3.4 MOA but the 220 is going 2354fps and 677 foot pound the 22 creed is 2584 fps and 1112 foot pounds

at 600 yards the 220 has 8.7 MOA drop at 1822 FPS and 405 foot pounds the 22 creed is 7.9 MOA 2247 FPS and 840 foot pounds

So at 600 its double the energy and 425 foot faster even though it started out 330 feet slower

Its indirectly when comparing bullets IT is projectile length that is used in BC calculation as the coefficient of form.

So when you look at BC you are looking at a conglomeration of factors. the form and the density both.

That poor, poor horse...Congrats TexFlip!

none of that has anything to do with penetration

I'll help you out a bit.

All 6mm 100-grain bullets have the same sectional density, but we can all agree that at the same impact velocity, they don't all penetrate the same. The TTSX compared to a BT is a perfect example. Different construction causes different expansion behavior which influences penettation.

BC has NO influence on penetration.

I'd suggest that Newton's formula does not take projectile expansion into account.

You're really reaching here.