Ballistics analysis: Sectional Density Ballistic Coefficient

[ron]

The Hornady LEVERevolution pointed projectiles with the flexible tip are seen as a great breakthrough enabling flatter trajectories with POrojectiles of the sme weight traveling at the same velocities in lever action rifles due to the development of pointed projectiles with flexible tips. Lever actions with tube magazines were formerly limited to flat-nosed bullets which were less aerodynamic. Soon after introducing the different rifle calibers, Hornady came out with bullets for the 357 and 44 mag pistol rounds.

And when that happened, I immediately went out and got a box of the 140 grain 357 magnums and found that they were very accurate on my six inch barreled Smith and Wesson Highway patrolman and also noticed when shooting them at an indoor range that they had very low muzzle flash compared to other ammo that I fired.

So I was happy with the ammo and also had this idea in the back of my head that if I ever wanted to do any long range shooting, I'd have that capability using that ammo. Then I tried some of that ammo in my 45-70 and qwhen I went to reload the cases I discovered that they were almost an eighth of an inch shorter than my other cases. Hmmmm...

Then I decided to look into loading some of this 265 grain flex-tip bullets meant for the 444 marlin in the 44 mag, and since I have both a 444 marlin and a 44 mag handgun I though that would be just dandy since I used to load the 265 Hornady flatnose in the 44 mag and it worked very well. But in doing some research, I found out that you can't use the 265 grain flex-tips in the 44 mag because that pointy nose is too long and that's why Hornady loads a 220 grain flex-tip in the 44mag in their factory ammo. I also found out that the length of these bullets is why their 45-70 ammo has the cases trimmed short or other wise if wouldn't function in repeaters which it has trouble doing anyway, so I found out trying it in my friend's Marlin and Hornady warns right on the cartridge box that you might have to alter your gun to use that ammo in a Marlin.

Then in researching further, I found out something unexpected. While the rifle ammo does have a significant greater ballistic coefficient than the flatnose or roundnose rifle ammo, the pistol ammo does not! And ballistic coefficient is what determines a projectile's aerodynamics. And so the only advantage the pistol ammo really has is that Hornady load them up nice and hot using special canister powders. In the 357 mag, the flex-tips have only a slightly better BC than the only otrhe bullet I comnpared it to, But with the 44 caliber, there are other conventional bullets that have a greater BC.

Here is the data I found on the comparative ballistic coefficients and sexual densities of the Hornady flex-rips compared to similar conventional projectiles. Note that the 160 grain Hornady 30-30 bullet has a BC of 0.330 while the Nosler partition 170 grainer has a BC of only 0.252 even though it's a slighty longer heavier bullet with greater sectional density.

Nosler Partition Bullets 30-30 Winchester (308 Diameter) 170 Grain Round Nose

Sectional Density: 0.256

Ballistic Coefficient: 0.252

Hornady FTX Bullets 30-30 Winchester (308 Diameter) 160 Grain Flex Tip

Sectional Density: 0.241
Ballistic Coefficient:0.330

Big difference, right? but with pistol bullets, not so! the only reason they migh shoot flatter is that Hornady load thgem to the maximum allowable pressures with the most efficient slowest burning powders.

Hornady FTX Bullets 38 Caliber (357 Diameter) 140 Grain Flex Tip

Sectional Density: 0.157
Ballistic Coefficient:0.160

Sierra Sports Master Bullets 38 Caliber (357 Diameter) 140 Grain Jacketed Hollow Point
Sectional Density: 0.157 Ballistics Coefficient: 0.155

Barnes XPB 44 Caliber (429 Diameter) 225 Grain Solid Copper Hollow Point
* Sectional density: 0.175
* Ballistic Coefficient:0.195

Sierra TournamentMaster Bullets 44 Caliber (429 Diameter) 220 Grain Full Profile Jacket
* Sectional Density: 0.187
* Ballistics Coefficient: 0.193

Hornady FTX Bullets 44 Caliber (430 Diameter) 225 Grain Flex Tip
* Sectional Density: 0.174
* Ballistic Coefficient:0.150

Sierra Sports Master Bullets 44 Caliber (429 Diameter) 210 Grain Jacketed Hollow Point
* Sectional Density: 0.163
* Ballistics Coefficient: 0.160

Oh and just for fun, Here's the SD and BC figures for the .41 magnum for comparison to the 44:
Speer DeepCurl Bullets 41 Caliber (410 Diameter) 210 Grain Bonded Jacketed Hollow Point Box
•Sectional Density: 0.178
•Ballistic Coefficient: 0.183


Ballistic Coefficient (BC) is basically a measure of how streamlined a bullet is; that is, how well it cuts through the air. Mathematically, it is the ratio of a bullet's sectional density to its coefficient of form. Ballistic Coefficient is essentially a measure of air drag.

Sectional density (SD) is the ratio of an object's mass to its cross-sectional area with respect to a given axis. It conveys how well an object's mass is distributed (by its shape) to overcome resistance along that axis. Sectional density as it relates to firearms ballistics, is defined either as a projectile's mass divided by its cross sectional area, or as a projectile's mass in pounds divided by the square of its diameter in inches. Greater sectional density enables greater penetration and also aids stability in flight.

[timbertiger]

Not sure that title is what you had in mind!

[bladebum]

"Sectional density"... Damn auto correct.

[ron]

"Sectional density"... Damn auto correct.

Yes. Sexual Density is when you're 15-16 years old and you know what you want but you don't quite know how to go about getting it. And conversely, SECTIONAL density has to do with the abilty to be able to penetrate.

[RLHas]

You notice how the really clever stuff only takes a few sentences?