While mulling over the caliber for a new barrel for one of my model 70 classics. .338 06 or 35 whelen. The .338 bullets have slightly better BCs and SDs. But I already have a whelen, and I really like it. I prety classic wood stock one would be nicer than the synthetic one I have now. looking at the nosler manual, I see that The sectional Density only seems to take into account the bullet Diamiter and weight. If SD is a measure of a bullets ability to penitrate It seems to me its at best a loose guide line. Certainly not usless but the SD of a 225 gran .338 Balistic tip and a .338 225 grain partition is the same . and certaily the design of the 2 bullets make one a much better penatrator than other, so my Question is how much stock do you put into sectional density ? ...tj3006

The general rule of thumb (as read by me in some book somewhere) was that an SD over .300 was a good indicator of penetration potential. If you work out the SD's of say a 400 grain .416 caliber bullet, a 300 grain .375 caliber bullet, a 250 grain .338 caliber bullet, 175 grain .284 caliber bullet, a 220 grain .308 caliber bullet, you will notice that they all possess that magic SD over .300 and every bullet weight/caliber combination has a history of excellent performance, sometimes even compensating somewhat for poor bullet construction. I don't think I would make a caliber choice based on SD, I make bullet weight choices based on SD. For just about every caliber there is a bullet weight that makes an SD of .300 or over. If your cartridge/rifle cannot shoot a bullet with an SD of .300 or over than I would probably not consider it a good all around combination for Africa, for instance.

Sectional density is only a guide. Bullet construction will make a more profound difference in a bullets ability to pentrate.

Sectional density is a good inidcator of pentration if the bullets you are comparing are of the same type. A 180 gr .308 Corelokt bullet will out penetrate a 150 gr Corelokt bullet for a couple of reasons. It is shot at a lower velocity and Remington designs them with heavier jackets etc.. to work better on heavier game. The same is true for most manufacturers.

With conventional cup and core bullets sectional density has some merit.However bullet construction is far more important.

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With a SD of .375, I wonder how these would penetrate?

Sectional denstity was the only number one need worry about, that was until the monolithics came along. Without mass and velocity, or the retention of it, there is no phisical way to keep a slug moving forward after it meets a certain amount of resistance. This would be true too for the bonded bullets, not because they loose mass, but rather because they provide a larger frontal mushroom that will cause even more resistance than a bullet that might loose a petal, like the X bullet, or the front core like the partition. Remember too, that monolithics are longer than lead core bullets when equal weight comparisons are made.

With that said, sectional denstiy is important, because without proper mass, read S/D, a bullet would arrive at target with insufficient energy to transfer for a clean kill. Given a cartridge of sufficient power to drive said bullets at reasonably flat trajectories, bullets of the same shape but with more weight in relation to their diameter retain more energy downrange.

SD gives us an idea of penitration of two LIKE bullets in the same target at the same velocity. The SD changes though when the bullet hits and starts deforming. A premium such as a Partition or Triple Shock will normally show a smaller frontal area and a longer shank then a commonly constructed bullet and keep a higher SD IN the target. This gives better and more straight line penitration, and explains why a step down in bullet wgt with a premium often gives the same results as a heavier copper/ lead core bullet.

I think SD was more relavent back in the day of cup/core bullets & dubious "solids". With todays monsolids & "premium" bullets, it isn't as important. I still like heavy for caliber bullets for big game, but I'm a bit old school.

Sectional density is more than just a diameter and weight ratio that folks relate(incorrectly) to penetration. For a bullet to put some whomp on a critter it has to have some speed left, and BC for a given form is directly proportional to SD. SD relates to interior/exterior and terminal ballistics, but the latter is largely dependent upon what the bullet does when it strikes a target. Big mushrooms reduce SD very quickly, small ones not so much. FMJ's or solids retain SD in the terminal phase IF they do not tumble.

If one thinks that an X bullet and a Corelokt of the same SD will penetrate equaly, they are very much mistaken.

Sd's and BC's are of course related. You won't get high numbers of one without the other.

I am certainly not a expert on this but I have found from years of reloading and shooting that I don't really care for any bullet less than approx .279 on a SD. I prefer over .3 and teens behind the 3 is better, but there aren't many of these bullet weights around.

Don't know if its right or wrong but the above rule has always worked for me. ( this DOES NOT apply to handgun bullets ). The .279 is not a hard and fast a a point or two varition is OK, but it is always my min. starting point.

That 300gr Woodleigh is too heavy for his proposed 338-06.

Ken Waters wrote in 1987, "Beginning around 200 yards and extending out to 300 yards and beyond, it is a ballistic fact of life that .338-inch bullets launched at the same speed as .358-inch bullets shoot flatter and hit harder, giving the .338-06 an undeniable advantage over the .35 Whelen...If we are realistic, it must be conceded that the .35 Whelen and the .350 Rem mag are excellent big game cartridges but the .338-06 possesses two important advantages; not such as to invalidate either cartridge, mind you, but sufficient to claim mostest and fustest."

The diff. in SD between the .338 & .35 is almost negligent. Either hits hard on game.

(How much stock do you put in sectional density ?)

What a penetrating question! However you answered it yourself. "All other factors being equal, highter SD means more bullet to Penetrate the target" would be my statement on the subject.
Partitions and other premium bullets change the rules.
Happy New Year!

quote:

Originally posted by fredj338:
I think SD was more relavent back in the day of cup/core bullets & dubious "solids". With todays monsolids & "premium" bullets, it isn't as important. I still like heavy for caliber bullets for big game, but I'm a bit old school.

Ditto for me.

-Bob F.

quote:

Originally posted by onefunzr2:
That 300gr Woodleigh is too heavy for his proposed 338-06.

Ken Waters wrote in 1987, "Beginning around 200 yards and extending out to 300 yards and beyond, it is a ballistic fact of life that .338-inch bullets launched at the same speed as .358-inch bullets shoot flatter and hit harder, giving the .338-06 an undeniable advantage over the .35 Whelen...If we are realistic, it must be conceded that the .35 Whelen and the .350 Rem mag are excellent big game cartridges but the .338-06 possesses two important advantages; not such as to invalidate either cartridge, mind you, but sufficient to claim mostest and fustest."

But I wonder what it could do in a 338-378?? And yes that bullet would be traveling too slow to be of any use in that 338-08, especially cause it probably has a jacket 1/8" thick being a woodleigh and all...

I try not to angst too much about that sort of stuff. While its great stuff for the hot stove league, I think your time would be better spend at the range.