Marcus,
Bear in mind that "Ballistic Coefficient" takes into account the length and form (shape) of the bullet. For equivalent diameter and weight bullets between jacketted-lead and totally-copper it is obvious that the totally-copper bullet will be longer because, as you've said, it is less dense. Being longer, and usually of a more sleek profile, the totally-copper bullet will have a higher B.C.. Therefore it will drop slightly less and loose slightly less velocity.

Whether the totally-copper bullet will kill better than the jacketted-lead bullet once it arrives on target is a whole 'nuther discussion. I've never used the X bullet so I can't say. I like Nolser Partitions though...they are reliable expanders that will also penetrate.
Jerry/AK

Midflight trajectory involves only 2 things, muzzle velocity and wind resistance. The higher the BC, the lower the wind resistance, the flatter the trajectory at any given MV.
Density of material dosn't come into play until you enter the "Terminal Balistics" phase, IE when the point meets the skin.

Unless I am mistaken won't a bullet such as a solid copper vs lead core being longer be more affected by the wind? If I am mistaken I would like to know why. At this point I will stick to lead core jacketed bullets.

The amount of drift depends mostly upon time of flight, but yes, I agree there would also be some difference due to a larger or smaller profile for the wind force to act against.
Jerry/AK

http://www.lostriverballistic.com./LRB/CategoryShow.cfm?CNum=10
What about these bullets?The BCs are really high.
.672 for the J36 .308-180 grain bullet f.E.
Any experience with these bullets?

Ballistic coefficient is the product of form factor and sectional density.

Where the solid copper bullet would gain is with very light for calibre bullets.

Lets take an extreme and compare aluminium to lead and use a 200 grain 458 bullet.

With a lead bullet the 200 grain weight would be so short in relation to its diamter we could not give a nice tapered ogive. But we could if it was made of aluminium.

So the 200 grain aluminium and lead 458 bullets will both have the same sectional density but the aluminium bullet can be given a much better form factor.

I think the Barnes X's poorer BC would be caused by what amounts to a small flat point.

Mike

I'm in Savage99's camp on this. For a seemingly simple question as posted it treads on a LOT of factors relating to exterior ballistics. Here's some facts for you:



C= W/IxD^2, where:



W = weight in pounds

I = form factor

D = diameter(squared)



Note that LENGTH has nothing to do with this calculation. Bullet nose form accounts for most of the form value, base is around single digit percentages, shank drag almost nonexistent for practical purposes. Also observe that Weight is the Numerator in this calculation, and it has very large influence. For a given form BC is directly proportional to Sectional Density, which is factored into the equation by Diameter. SD is purely a valuation based on weight and diameter. Any body that doubts the influence of weight should compare the .44 cal 300 gr XTP by Hornady against the .17 cal 25 gr spitzer by the same company.



Wind drift is more of a calculation of drag influence than TOF.



D= W(T-Tv) where:



D = Deflection in Feet

W = Wind velocity in fps

T = TOF at distance in question

Tv= TOF in vacuum



Drift is really a DEFLECTION , but if you like the term DRIFT, okay fine. Just know the difference.



Know ye all, I do not like the use of BC's but it is what is available for the most part. Coefficient of Drag is better...when you can find it. BC as commonly represented by bullet manufacturers is overstated IMO. What is certain is that YOUR conditions will not be the same as theirs, and theirs are calculated or established, then advertised in a standard atmosphere environment. It is a number that changes with temperature, humidity, and atmosphereic pressure. That said, BC represents a relative measure of how a bullet will fly as compared to a standard benchmark, often the G1 form. BC is the fundamental touchstone of both trajectory and deflection/drift calculations.



Now where it gets screwy is the actual influence of bullet material in regards to BC. Having said that Weight and Form are biggies in the BC world, some will still look at a long needle shaped bullet and say, "But..." The only thing you draw from length is the ability to increase the nose length in form suitable to reduce drag. Remember, form is but one part of the Denominator in the BC equation. What you pay is the requirement to have a quicker twist(see the Greenhill Formula), which is of small consequence at short range, but then, so is BC. At long range though, it creates additional ballistic contortions related to Gyroscopic Stability Factors which in fact will diminish BC values due to Yaw of Repose and in extreme cases, Tractability issues as well.



Well, I could go on and on, but I think I won't. Hope this hasn't muddied the waters too much. In answer to the question posted by Marcus, don't worry too much about your bullet choice based on published BC's or bullet material. There is not a great deal of difference inside of 300 yards between RN designs and spitzer designs regarding trajectory, though the same cannot be said regarding "Drift". Terminal performance is another subject entirely, and if your concern is found there, I would say that if your rifle will shoot a Barnes X/TSX and you want to use it, by all means do so. BC's are NOT influenced by bullet material in a meaningful way as far as hunting big game is concerned. It IS influenced by weight to sufficient degree that it may be worth considering.



PS: Yes, the meplat diameter is used to calculate form factor, so it does have some value, albeit small.







.

Barnes exaggerates their BC's relative to other manufacturers as any side-by-side test will show. They've fooled a lot of people.



Length does matter a tiny bit as it makes up some of the form factor. But it's just a tiny bit and it usually goes against what most would guess--length usually hurts the form factor (all else being equal) due to increased skin drag.



Weight, however is not a small factor. It's huge. For a given caliber and shape the BC is directly proportional to the bullet's weight. Doesn't matter if its made of balsa wood, it's the mass that matters.



The long Lost River bullets have high BC's because of their tiny meplats, long boattails and very aggressive ogives.



I disagree somewhat with DD on Cd's for anybody but complete ballistic nuts (like us). With accurate BC information you can get as accurate info as anybody could want. It's just easier.



Most people are confused enough (sometimes to the point of disbelief) with BC's. If companies published Cd's, people would be all the more confused. Because to do anything with the Cd, you'd need to take into account the diameter of the bullet (frontal area) and its weight. That's much too much math for most people.



BC's do this for people with the form factor (analagous to Cd) and sectional density. This gives one single number that describes how a bullet will hold onto its velocity and all the calculations that result from that. Tell somebody that two bullets with the same Cd are going to fly vastly differently and they'd just throw up their hands and call it all Witchcraft!



And it should be mentioned that BC's do change with air density. Cd's don't. There's nothing wrong with that. You need to take air density into account before you can do anything with a Cd, anyway. So you still need to do it if you want accurate results.



BC's just do more of the math for you. You can get the same results but it's more idiot-proof.

Well said Jon, sometimes I disagree with myself too.

My preference is based solely on the belief that Cd's are a more stable value that, as you mentioned, doesn't change with the phase of the moon. I suppose it depends on whether you'd rather walk to lunch or carry your work?

We use BC's because they are available, and many use the info well, and at great distances. I think they find a lot of those numbers don't stand up to close scrutiny though. I did not mean to imply they were without merit.