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Denser core material?

 
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  #22  
Old 09-03-2003, 10:25 AM
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Re: Denser core material?

Mercury being a liquid at room temp would pose some serious problems with core integrity, not to metion trying to make them.

Try getting those approved for use on a range. If you could get your hands on some depleted uranium, would be very interesting. You may not live too long, but it would be very interesting.

I think the best new tech are poly tipped bullets. They provide a very sharp nose profile and move the CG of the bullet back. With more copper/jacket then lead, these bullets have been made significantly longer for the same bullet weight. You still have to be able to launch these things.

I think that higher BC bullets will come from the invention of a stronger lighter jacket material that will allow "longer" bullets for the same weight. At some point, being able to stabilizing and getting resonable vel will be a limiting factor - time for new powders too.

As to my understanding of BC, weight is not part of the calculation. BC is a non dimensional unit of measure to indicate a projectiles drag as compared to a standard (BC of 1.00). Weight and cal. are not relevant. That is why you can have such varying bullets with the same BC.

Remember a 30 cal 200gr Round nose is not going to fly as well as a 155gr palma bullet even though the weigh is higher.

Weight will play a role in momentum of the object. This may have a small impact on things like wind drift but overal, BC/drag of an object is based on its shape and how it flows through a fluid.

Jerry
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  #23  
Old 09-03-2003, 11:01 PM
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Re: Denser core material?

Oh come on now! Weight and caliber (diameter) are certainly major factors in the calculation of ballistic coefficients...

BC is directly related to sectional density, which is directly related to weight (mass).

Here...

C = SD/i

or

C = w/i * (d squared)

where

C = ballistic coefficient
SD = sectional density
i = form factor
w = weight of bullet, lbs.
d = diameter of the bullet, inches.
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  #24  
Old 09-03-2003, 11:35 PM
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Re: Denser core material?

Jerry,

You've been misled I'm afraid.

Form and mass are key.

A thinner jacketed lead core bullet with the same outside form, thus dims will always have a lower BC because it's weight is less, so is it fact that a higher density core material than lead in the same form and dims will up the BC too. Jumping from lead to Tungsten for instance would be a huge jump too. There's a really good article on Corbin's website you'd like, actually quite a few of them there that are quite enlightening. Liked the ones on rebated boattails too.

Oh ya, melt down the mercury they put in all our teeth, tell the bunny huggers that's where you got the stuff if they ask!

That stuff is one, if not the most toxic stuff on earth I'm told. Wait, I think that was flouride! You know, the other toxic waste they feed us that they have to get rid of somewhere, under the guise its good for your teeth! Glad I don't have city water...

[ 09-03-2003: Message edited by: Brent ]
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  #25  
Old 09-04-2003, 05:03 PM
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Re: Denser core material?

Brent, yep, looks like I got the math wrong BUT since I usually compare bullets of the same weight, mass is constant. I am concerned then about form and the BC value of such.

That is where I draw my conclusions about the poly tipped bullets and their benefits to increase BC. Also, all the newer controlled expansion/bonded bullets like Scirocco, Accu and interbond, SST which are much longer due to less lead then conventional hunting bullets of similar weight.

This increased length and bullet construction also changes the effective SD of these bullets. They give the same performance on game and target as much heavier conventional bullets. Pretty hard to give the same on game SD of a Barnes X and an Amax.

I think the direction of increased core mass will quickly run into problems due to the difficulty of obtaining super dense material, their cost, and ease of manufacture. Plus most are extremely deadly.

The increase of BC through the use of tough light jacket material should be easier. We already have companies like Lost River making lathe turned bullets with super high BC numbers. Since twist rate is very simple to adjust/increase, there would be little issue in launching these bullets. Slow powders is the final link.

Is there an Aluminum alloy that is tough enough to make the trip? How about a carbon fibre bullet?

Jerry
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  #26  
Old 09-05-2003, 03:00 AM
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Re: Denser core material?

I have heard that Mercury compresses and becomes more dense under extreme pressure and colder temperatures. Perhaps it could be compressed and encased in molten copper.

It could even make a potentially devestating hunting cartidge. The bullet would explode inside the animal. The compressed mercury would expand after being released from its jacket and send showers of expanding Mercury throughout the animals internal organs and flesh.
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  #27  
Old 09-05-2003, 05:44 PM
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Re: Denser core material?

I think I posted a link to this somewhere, but here's a good explantion everyone here should read concerning bullet design, what alters BC, why, and other considerations as to accuracy etc.

The following was copied and pasted here from Corbin's BR article.

Why use a secant ogive at all? The secant ogive lets us fool Mother Nature just a little bit. We can shorten the axial length (linear, down the middle of the bullet) of the nose, so the bullet still fits our gun and still requires normal spin rate, but join the long thin nose to the shank at a slight angle that doesn't generally create a shock wave. If we keep increasing the angle, soon we have a secondary shock wave generated at Mach I (speed of sound) bullet velocity and above, and the advantage of the lower drag co-efficient is lost. One shock wave is bad enough, and you can't design around that...no point designing in a second one to add more effective drag. The problem with shock waves is that they are related to a variable, the speed of sound. This is not a constant value, but varies with effective air density (which also varies with moisture and barometric pressure). So, if you push the secant ogive bullet design to the edge on a good day, it may work fine, but as soon as the weather changes, the bullet follows a different trajectory because it now generates that secondary shock wave that was absent before, and the BC drops as a result.

As you may know, if you have a vast number of bullets of all calibers and shapes and weights, but they all happen to have the same BC, then firing them all at the same initial velocity will result in them all following exactly the same trajectory. A .17 caliber and a .50 caliber will follow the same trajectory if they have the same BC. It's the meaning of BC, the relative rate of retardation compared to some standard bullet. But having delved into this aspect of bullet design, it's time for a reality check.

When the only consideration is accuracy, issues such as the BC are secondary. There is an unfortunate tendancy among shooters who do not have a physics or engineering background to equate the ballistic coefficient with the accuracy of a bullet. That is, a high BC is sometimes thought to be necessary for one hole groups.

Ballistic coefficient is primarily a comparison of the drag or rate of velocity loss of a given bullet with some other bullet that is selected as a standard or 1.0 on the graph. It has no meaning in absolute terms. To say that one bullet has a BC of .830 and another has a BC of .345 only has meaning if we are absolutely certain that both bullets were compared to the same standard. This is not always the case, since the number has become popularized beyond its strictly mathematical usefulness and is now used as a marketing tool.

Assuming that the standard bullet is specified, then a comparison of BC values for two bullets would have meaning. It indicates how closely the samples perform in overcoming air resistance (usually compared to a 1-inch boattailed spitzer artillery projectile). All other things being equal, a higher BC is desirable, but not at the expense of accuracy. The BC is determined by multiplying a coefficient called the "Ingall's number", which represents the inverse drag of the air upon the bullet, times the mass divided by the square of the diameter.

The BC goes up with an increase in weight, down with an increase in diameter, and up with a lowering of the air drag on the bullet. If a person were to strive for high BC, here are some of the ways to accomplish that:

1. Use a high density material, such as gold, tungsten, iridium, or osmium. High density puts more weight into a smaller package, so that the mass is increased for a given diameter without making the length excessive. This has the disadvantage of increasing bullet cost. Powdered metals can be compressed with normal swaging pressures, but have lower density than solid or sintered metal. Osmium, which vies with iridium as the heaviest stable metal, can produce deadly fumes under certain conditions. Gold and iridium are safe to use but rather costly. EZ-Flo Micro-Fine Tungsten powder is available from Corbin in 7,000 grain, 35,000 grain, and 70,000 grain flasks as well as by 50-kg pail, and is used by a number of custom bullet firms and government groups.


2. Make the bullet longer for a given diameter. This adds mass, but has the negative effect of requiring faster spin rate to keep the bullet pointed nose first. More spin amplifies any imbalances in the bullet radial parameters, such as slight differences in jacket wall thickness. Accuracy can become far worse from either high required spin rate, or from a bullet becoming too long for the barrel twist and thus unstable. High BC can in this case lead to less accuracy.


3. Reduce the included angle of the shock wave for bullets traveling above Mach I (the speed of sound) by making the ogive more sharply pointed, and reduce the turbulence at the bullet base by using a rebated boattail (which avoids generating a ball of gas through which the bullet must travel, like a conventional boattail). A longer nose requires a higher minimum weight, and a longer counter-balancing shank, so that as the ogive becomes more and more pointed, the bullet becomes longer and longer, and eventually the required spin rate to stabilize it becomes excessive. In a single shot bolt action rifle, the physical length of the bullet nose isn't a factor in functioning of the gun (assuming the chamber and leade were designed with the long bullet in mind). But spin rate puts a limit on practical ogive length.


Typically, benchrest bullets for under 200 yard shooting don't need to exaggerate the BC, and can gain more by using the lowest practical spin rate. Therefore, a 6-S ogive would be entirely practical. Many clients choose a 7-S custom ogive, or the 8-S ogive. A few choose the ULD (Ultra Low Drag, developed by Corbin for military and Treasury department sniper applications many years before the very similar VLD popular with civilians). But even though the ULD is our design, we feel strongly that it is not appropriate for medium and short range (100-300 yard) target shooting simply because it forces the shooter to use a longer bullet than necessary, which in turn requires a faster twist barrel, which in turn exaggerates any jacket wall eccentricity. So why do it? Who cares about the BC, if you are not shooting in a gale wind, at 100-300 yards? If you can read the mirage and the wind flags like a high power shooter, then you can certainly take advantage of the slower spin that stabilizes a normal weight 6-S bullet.

But the ULD design will help at 500-1000 yards (and of course, with 50 caliber benchrest at 1000-2000 yards, it will become a necessity as soon as enough other good shooters catch on). At some point, the bad effect of more spin balances the bad effect of wind drift on a lower BC bullet, and you choose the lesser of the two evils. This is no different from other bullet design fields, where you are always choosing between two contradictory values and trying to balance their bad effects in order to get the most use from their good effects.

Here's the link to the whole article. http://corbins.com/benchrst.htm

[ 09-05-2003: Message edited by: Brent ]
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  #28  
Old 09-05-2003, 11:26 PM
MAX MAX is offline
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Re: Denser core material?

The nexus of this issue in my eye, and I think the reason S1 et al pursue the tungsten core goes directly to the issue of BC AND GS. BC is weight related in a big way, it is also and issue of form. It has very little to do with bullet length. The penalty of long bullets is the shift to the rear of CG vis-a-vis CP which requires a faster twist to stabilize the bullet. GS is a function of angular momentum, and the required amount can be achieved with high rpm or more mass. High rpm projectiles are more influenced by "spin drift/yaw of repose" issues. As forward velocity decays quickly, rotational speed deminishes slowly and this leads to an increasing GS which compounds yaw of repose. Tractibility of a bullet is inverse to GS as well.

What a mess! [img]images/icons/shocked.gif[/img]

Some of this has been hotly debated here before, and I do not presume to settle the matter. There is more than one way to skin a cat as they say, the question remains however, at what range? There may well be exterior ballistics issues that I'm unaware of, but my take favors the heavier core material at this point. Problem seems to be difficulty of manufacture and expense. I think the jury is still out...
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