I�m trying Barnes Triple X in 169 grain in .30 out of my 300 WSM and 135 and 140 grain out of my 270 WSM. Have all of them laying right here next to my keyboard.

It hit me a few days ago that perhaps the theory of sectional density may be outdated with these new bullets. My short cut thinking to describe sectional density has always been, how many lead or copper molecules are behind the lead molecule, the first molecule to hit the target. In other words, how long is the bullet compared to its diameter? My favorite example; the 180 grain .30 caliber compared to the 180 grain Whelen.

But looking at the new grooved bullets like the Triple X forces a reevaluation.

I take for granted that sectional density assumes a straight bearing surface. That is no longer true with grooved bullets and that alone may obsolete the concept. If anything, grooved bullets are more a kin to sabots. I have samples of the Triple X next to regular Barnes X so I can contemplate the difference. The .30 Triple X is just a tad shorter than the 180 grain X BT. The 130 grain Triple X 270 and the 140 grain 270 Triple X are the same length. Barnes achieved that by fattening front of the 140. The copper cut away at the grooves has to go somewhere and the nose is where the engineers put it. The 140 XXX and the 130 XXX are just about as long as the 150 X FB.

So is sectional density dead?

With the new premium bullets, sectional density is no longer of much use in predicting bullet performance.Bullet construction is far more of a factor.

RogerK,

Sectional Density is a measurement of the mass of a bullet. All .308 150 grain bullets have the same SD. Shape, or construction has nothing to do with it. In standard constructed bullets, SD was an indicator of how deeply a buller would penetrate. It will still serve that purpose with bullets of the same type. In the Nosler Partition bullets, a 180 grain will usually penetrate deeper that a 150 grain bullet. If the Partitions are compared to any other make of bullet, all bets are off. Good luck.

I`ve a feeling that SD still applies. The SD changes the second the bullet hits and starts expanding. The new mono bullets expand slower and have a smaller frontal area in relation to the old std constucted slugs, possibly leaving them longer and narrower with more retained wgt than the heavier jacketed bullet resulting in a greater SD while inside the target.
The old thinking on SD in jacketed bullet constrution took it for granted the bullet behaved the same in the target; if one was heavier and they both expanded the same the heavier one was still longer and had a greater SD.

Just an opinion, I don`t know it to be true.

[ 08-04-2003, 04:52: Message edited by: Ol` Joe ]

Sectional density is part of the equation. Other parts of the equation can be improved, but sectional density is not going to disappear.

H. C.

RogerK --- Sectional Density may be dead for you, as you perceive it, using the X bullets. How about average joe hunter out there that has never shot the X bullets, is it dead for him or her. ---- Many lives have been saved by a good Sectional Density bullet used on dangerous game, by hunters who had no idea what the term was in the first place. The fact that the bullet penetrated and disabled, was the important factor, rather than the theory, or the understanding thereof. Just my .02 worth. Good shooting.

Of course it still matters. It is true that premium bullets allow you to step down in weight for a given caliber, but the added advatage in trajectory of a 165gr 30 cal over a 180gr is minimal, but given two bullets of the same brand, I'd stick with the 180s because of greater SD and penetration. I guess it's a yes and no type of answer. jorge

Sectional Density is not dead, but it is pretty much irrelevant. The only really relevant number is Sectional Density AFTER IMPACT. If you were to develop a formula, it should involve "post impact" SD with the frontal expansion ratio (150% of caliber, e.g.). Combined with impact speed, these should give a reasonable forecast of wound channel dimensions. JMO, Dutch.

Not at my house it isn't. Although I agree with Dutch most of the time, Not here.

Sectional density is relevant before impact. While people talk of Ballistic Coefficient, if one looks at a lot of ballistic charts in reload manuals, one would notice that if bullets having similar designs ( Eg, Boattails, Flat Base, RN)
two bullets of different calibers but the same sectional density, shot at the same muzzle velocity will have the same trajectories.

Although, I can see some people getting finite over this and start to argue a tenth of an inch at 100 yds, for all practical hunting I find this useful. Not all bullets list their BCs or are in books with published trajectory charts. If I have a sectional density, then I have a trajectory by comparing to a known bullet from another chart.

I also rely on sectional density as a factor for penetration.

This is my own personal use of it, and it is share/able with anyone who wants to use it.

Roger,
You are both right and wrong...the monolithic has changed or rather bent the rule of SD, but only to a degree....given a .308 monolithic that weighs 180 or another weighing 125 for big game I would go with the 180 and its higher SD as you still need a heavy base to push a bullet...regardless of the hype...

Now I will agree that a 165 gr. Monolithic is the equivelent of a 180 gr. conventional premium bullet....

My experience does not subscribe to a 120 gr. 7x57 monolithic being a better game bullet than a 175 gr. Nosler...as many monolithic bullet manufactures would have you believe...

I think the monolithic is a great advance in bullet making and gets better all the time, but I don't buy off on a lot of BS that surrounds them either....

My experience is when they perform properly they are an awesome bullet, but when the fail, they fail miserably...I believe there is room for both in my hunting and I believe SD will always be a criteria in choosing bullets....

I also believe there is a place for the half monolithic bullet such as the Northfork, which will do much more internal damage than say a Barnes X, or any other bullet, but I think the Nosler and BarnesX will out penitrate the Northfork, Woodliegh, and Bearclaw. they also have a very much smaller cross section at expansion for this very reason..So take your pick.

Today bullets are so good it is hard to go wrong, the last 10 years have been the heyday of good bullets from the bullets I used many years ago where every shot was a crap shoot...

I have chosen the Northfork, Nosler and Woodleighs as my standbys in conventional form and have had fantastic luck with the GS Customs.

I'm looking forward to trying the Groove bullets and the Bridger hollow points...I have a lot of the Brider flat nose solids and I know they will perform, but will prove that in a about another three weeks in Tanzania on some big old dugga boys...

Its a smorgasbord of great bullets out there today. It just doesn't get any better than this.

Other than the Barnes claims that a smaller bullet of theirs will do what something more will from a SP, the SD is still the same for a 165 grn bullet. But since the need for "X" bullets was spawned from Johnny Magnums "need" for more velocity than everyone else, he also "needs" to go up one size to satisfy his run away testosterone, which offsets the Barnes claim, and therefore the relevancy of SD is the same as it ever was.

Might want to check out Al Marion's recent article in "The Accurate Rifle" concerning TSD - Terminal Sectional Density. TSD calculates sectional density using expanded diameter and retained weight. Other people including Veral Smith have worked with the idea over the years. I'm sure others have too.

Hammer

Physics has not changed. But, the new bullets are pointing out different principals of physics. One of the ways the new wonder bullets get their penetration edge is by reducing malformation. Just shoot a real crooked arrow. Another is to reduce the frontal exposted area and or add cutting leafs to reduce resistance. Weight, in line, pushing a given frontal area. The truth still exists; the measure of effectiveness is the damage done and at what point during the penetration of the animal. Thats why the Nosler partitions and Swifts still get alot of support. I mirror and support Mr Atkinson's experience.

[ 08-06-2003, 04:13: Message edited by: Old & Slow ]

Those savvy old shooters of resteryear knew that heavy for calibre bullets worked long before the term "sectional density" was ever coined.

Well, I'll be a monkey's uncle! Seafire is actually right about something!

Just messin' with ya man.

The BC of a bullet is directly proportional to its sectional density. So, for a given shape, the heavier for caliber the bullet is the higher its BC.

Like he mentioned it's useful for comparing bullets that don't have published BC's. It's also useful for "what if scenarios." What if Nosler made a 220 30 cal Accubond? .588 X 220/200 = .647 BC. As long as the tips, ogives and bases are the same you'll be very close. Since the same bullet will have a slightly different BC from rifle to rifle and at different velocities, close enough.

That's why light for caliber bullets are at a big disadvantage for shooting at long range--regardless of how aerodynamic they are. You've got the same basic shape causing the same amount of drag. This force will decelerate the bullet. F=ma. The heavier bullet decelerates at a lower rate.

There have been some manufacturers lately (especially of Mono Metal bullets) that have confused people a bit by exaggerating the advertised BC's for their light bullets--cough, cough, Barnes is a good example, cough, cough--making many think the length of the bullet gives them a better BC. There is a small component of the Form Factor called Skin Drag--but it gets worse as the bullet gets longer. But it is a very small percentage of the overall BC. If the tip, ogive and base are the same you can basically ignore it and be very close.

For resisting wind drift and retaining energy at long range, heavy bullets rule.

(Unless, of course, you go and put a round nose on the thing like Seafire would!)

Jon A:

Thanks Buddy!! Hats off to you for the info and explaining it.

Course my Round Nose stuff, I limit that to 250 yd shots anyway, so round nose or not does not really make a big difference.

However when I do carry a Round Nose load in the field, I also carry the same load with a Spire Point of the same, just in case the Opportunity D'Jour requires the potential of a longer shot.

I just always believe a Round Nose is a little more Nimrod proof. Hope you and your family have as good of a deer season this year, as your luck was last year.

I ended up with a second Elk tag this year in Oregon. I might just load up some 220 grain Matchkings in my 300 and Carry it afield on the second Elk hunt in YOUR Honor and just see what it will do. Course I will also load up some 220 gr Nosler partition just for back up or a second shot.

I might not agree with all your ideas on here, but I do respect your opinions, especially when you take the time and the courtesy to the rest of us, and explain it in engineering terms, yet keep it where the rest of us can understand it.