Sectional Density?

[Duster]

Fellar's just how much weight should a body put on this SD thing I am always hearing about. I have always been a fan of bigger bullets verses the little hotter ones.

My question is like if a hunter was shooting say a 338 caliber bullet out of a .340 Weatherby using a 225 grain bullet. Now lets say there is another fellar that has a .358 magnum type shooting the same weight bullet with the same velocity behind both rifles mind ya. The sd on the 225 gr .338 caliber bullet is .281 and the sd for the .358 caliber is .250---So lets say the target or bull elk is at 500 yards (just saying OK) how much of a difference is there going to be on a quartering away shot??? I don't really know myself, but think it is a good thing to know about.

 

[danr55]

Well Duster, How about Captain Dan's 2 minute drill on terminal ballistics? Here goes:
When a bullet strikes a target, the criticality of the resulting wound is a combination of three elements: 1. Terminal velocity; 2. Target density; 3. Momentum. The first two are pretty much self explanatory. The third one is where a lot of people get confused. Momentum is a combitnation of form factor of the projectile, weight, velocity in it's relationship to cross sectional area, jacket construction and core compositon (as it applies to the deformation of the bullet). Sectional density is the relationship between the cross sectional area of the bullet and it's weight. The higher the 'sectional density' of a bullet, the higher the momentum factor will be and the better penetration characteristics you will have at any range and/or velocity. The high sectional density is one of the factors that give the 160 and 156 grain 6.5 bullets their magnificent terminal performance. It can generally be said that the higher the ballistic coefficient of a bullet, the higher the sectional density will probably be. Both are relationships between diameter and weight. Although one accounts for form factory and aerodynamic characteristics and how they change at different velocities.

I know that's a little technical, and I wish I could explain it in simpler terms. All I can say is that higher sectional density will yeild better penetration characteristics at equivalent velocities.

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Dan AZ www.huntandlodge.com

 

[Duster]

Hot Damn Bcat! You best let the pentagone know we got us one of those rocket scientists doing the moderating over uon this forum of Moosie's.

Dan55 you sure got the talking part down good, you ever try selling vacuum cleaners or used cars? I am just kidding some hope you know.

So Dan you are saying the the 338 bullet will do the job better (penetrate further)than the .358 bullet which makes a bigger hole right? Now is there any way of knowing what that difference would be like in terms of inches?

 

[danr55]

Duster, That's not exactly what I'm saying. What I'm saying is that if you are shooting at distances where the terminal performance may be marginal, the bullet with the higher sectional density will generally have more momentum than the bullet with the lower sectional density and thus you should see better penetration. Now if you shoot an Elk with a 35 Whelen or a 338 win mag at 250 yards, either one should do the job. If you extend that distance to 600 yards, then you have to consider several additional ideas. You asked about sectional density and I gae you infomation on sectional density. It's kind of like ballistic coefficient. It don't mean nothing if you don't use it right. It's not rocket science. It's called the Science of Ballistics.

 

[Duster]

OK DAN, so now that we got through the school work, which one of the calibers above would do the best job at knocking down an elk at that 600 yards??? I am voting for the 338 mag right?

 

[danr55]

Well, Comparing the .340 Weatherby with the 358 STA, both with a muzzle velocity of 2900 fps, both shooting 250 grain Nosler Partitions, the kinetic energy at 500 yards would be 2209 for the 338 and 2105 for the big 35. With the two of them being so close, I would say that the advantage would be with the higher sectional density and the greater retained energy of the 338. But that is about as close a call as you can get. Even with that little difference, SD paid off. Now let's stretch it. With a 200 grain 6.5mm bullet and a 30 caliber 200 grain bullet, given that the muzzle velocities were equal at about 3000 fps, the clear advantage would be with the 6.5 after only 200 yards. As you approach your 500 yard mark the 6.5 has retained almost 60% more velocity and energy than the 308 pellet. The greater the spread, the more telling the difference.

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Dan AZ www.huntandlodge.com

 

[Duster]

Gee Whiskers Dan55, I do kinda understand what you are saying about the SD thing OK and thanks for taking the time to help out.

Now so far you say it is a real close match up between the two, if I follow you right.

So the other thing is what about the fact that the .358-STA has in fact a bigger diameter over the .338-Win mag??? How much you think would this play in the final effects of being able to put down the big elk??? So I can get a better picture and make a proper choice in the future perhaps.

 

[danr55]

Duster, I don't thing that .020 difference in bullet diameter will amount to a hill of beans if you hit an elk. If you are asking about the 35 whelen and the 338 Win Mag, the win mag wins. If you are asking about the 340 Weatherby and the 358 STA, I don't think you could measure the difference in terminal effect. If it were me, I would build an 8X62 Durham Magnum and not worry about either one of those woosy commercial rounds. If you don't reload, then pick the factory one that fits you best. That's always the best choice.

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Dan AZ www.huntandlodge.com

 

[Duster]

OK DAN, Now what is a 8x62 Durham caliber?

Do you have the ballistics on that round and could you let me know how it stacks up against the .340 Weatherby Dan.

 

[danr55]

So....I trolled the jig and you bit. HOOK UP>>>>>>
8X62 Durham Magnum is a wildcat that was developed by Charlie Durham of Denver Colorado about 1968. If you have a copy of PO Ackleys book, it's on page 456 of volume one. "It aproximates the standard 375 H&H in killing power." I push a 220 grain Sierra bullet at about 3050 or a 200 grain Nosler partition at about 3190 fps. I shoot it out of a 25 inch barrel on a surplus Mauser action. The case has minimum body taper and a fairly sharp 30 degree shoulder. I like that feature because the cases don't stretch. The brass is formed out of either 300 or 375 H&H, 8mm Rem Mag, or any of the full length magnum cases. I like it because it is efficient and accurate. It is my favorite 600 yard Elk rifle. Average group size for my rifle is about 3/8 inch @ 100 yards. If you choose to go after really heavy game, there is a 264 grain bullet available from RWS.

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Dan AZ www.huntandlodge.com

 

[Duster]

So you thought you caught a FISH hey fisherman! Well I suppose that is a lot of stopping power for sure. I just don't know if my shoulder will take the punishment handed out by such a massive deliverer of energy. I did have an idea to have a personal like long range elk gun. I might even take it out to Bcat's neck of the woods and drag race it with the chopper copter freind of his, who has the cannon on wheels according to Bcat.
I sure do like the idea of the .338 bullets, since I got a ton of them bought already Dan. Oh well, it will give me something to think about besides the pain in the bones ha.
I will see about getting the PO Ackley book you mentioned though for sure.

 

[danr55]

Gee duster, did I forget to mention that I build one hell of a muzzle brake? I'm sorry. You don't think that I would intentionally put my self behind something like that without on do you? Not a chance. Another guy wanted to try it without the brake about 6 years ago. Damned thing broke his nose. No, I'm old and fat, but I ain't stupid. No way would I try to catch that thing coming back without some help.

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Dan AZ www.huntandlodge.com

 

[Duster]

Danr55 I am sure glad you filled me in on the muzzle break end of things. I put that information over the radio and the boys (I can't say what they said, its off color) remarked in a round about way that you must be "one tuff big SOB" to be able to handle that Bozooka! I didn't know that there were so many wildcat cartridges out there until I looked at a couple of Paul's books he brought over for me to browse through.
I guess I will just go back to thinking about the old 300 win mag with a 180 grn bullet. It will do 3100fps with the 180 grn bullet I know. I can shoot it all day long (well at least 20 rounds from the bench) I don't like muzzle breaks and hate to put anything in my ears at all. Besides I look funny just walking, can ya imagine what I would look like hunting and pulling a rifle on wheels behind me. ha ha he he I'll dream on Danr!

 

[Slamfire]

It is sometimes helpful to think of sectional density as an experssion of length. Bullets with the same sectional density will be the same length, provided they're made of the same materials. This is true without reference to bullet diameter. The 150 grain .308 bullet is not as long as a 140 grain .264 bullet. Every thing else being equal the bullet with the most sectional density should penetrate farther in the same target.