Re: Non-tox long range shooting
My experience and take on mono metals and jacketed lead are:
1: The general accepted rule is mono metal bullets made of copper, brass etc....typically require a bit more twist than a jacketed lead bullet equal weight for equal weight. This is due to the lower specific gravity of these metals than jacketed lead. In other words, it takes more length to to make a 180 grain copper bullet than a jacketed lead bullet all else being equal. To validate this idea I have taken a 12x barrel 308 and fired 200 grain SMK's or SGK's in any conditions just fine. When shooting 200 grain Barnes out of the same rifle and they hit the target sideways at 10 yards every time. There are also mathematical formulas to validate this idea.
2: I have found that some mono metals have higher BC's per weight than jacketed lead and some that are lower. Mono metals are typically longer than jacketed lead for a given weight especially when they have the same nose and boat tail profiles.
Bullet length in and of itself does not add to the BC value. The longer the bullet to form factor ratio the more it actually decreases the BC a bit. If you have a jacketed lead bullet and a solid copper bullet the same caliber, same nose profile and tip and the same boat tail, they would have nearly the same BC dispite the mono metal bullet being longer with an ever so slight advantage to the jacketed lead bullet due to less 'bearing' surface in the air. Nosler makes the AB and the Etip. Both are close in form factor and 180 30 cal for 180 30 cal they advertise the BC to be higher for the Etip. I am not sure why they did this unless the nose profile is sleeker which if it is my eyes cannot see it. I have not measured it so I cannot say. What I do know is the last time I ran the 180 AB over double chronies I came up with .524 which is nearly identical to their published number for the Etip. Maybe they had a different test barrel or ran them over a different velocity range. In any event, it seems out of place. When you compare the 180 TTSX against the 180 AB, the TTSX is a tenth of an inch longer. The published BC for the AB is .507 and the published BC for the TTSX is .484. I realize it isnt quite apples to apples due to the noses and boat tails not being identical or the bearing surface due to the grooves in the TTSX but it still give an idea of the BC/Sectional Density/Form Factor relationship. Then when you look to some of the GS bullets and the cutting edge bullets you find super high BC mono metal bullets. They also have very sleek forms. The 200 grain SGK's I shoot are conciderably shorter than the 180 AB, 180 TTSX etc.....yet have a MUCH higher BC. Even though some of this is due to a better boat tail, most of this is due to the higher sectional density.
The only reason mono metal bullets have a reputation for having higher BC's is because when you have a longer bullet you can afford to lengthen the nose and boat tail and still have sufficient bearing surface in the barrel. There is only so much you can do with a 30 cal 155 be it all copper or jacketed lead. You are stuck with a pretty low BC but with a 175-200+ grain there are alot more options and possibilities. When you make them longer such as with mono metal bullets, there are even more possibilities. This is how Cutting Edge bullets makes such high BC 338 bullets and 308 cal bullets. You can take a 180 grain mono metal bullet and make it the same shape and length as a 208 AMAX. A 180 now has a pretty substantial BC even though it will be conciderably less than the 208 due to the lower sectional density. Mathematically the 180 grain with the same length and form as the 208 would only have 86.5% of the 208's BC. Or about .561-.563. You cant take a 180 jacketed lead bullet and give it the same length and shape as a 208 but you can with a 180 using all copper. It is in this sense that mono metal bullets have higher BC's than jacketed lead. It is this principal that is one of a couple that leads shooters to think that leads many shooters to believe that longer means higher.
BC is a function of sectional density and form factor. Sectional density is a function of weight and diameter. Form factor is the nose profile and tip, bearing surface, grooves or no grooves and boat tail. The only time more length helps the BC is when it is used to make the nose and boat tail sleeker. Nothing more nothing less.
Technically, BC = (drag deceleration of the standard bullet) / (drag deceleration of the actual bullet). The reference of the standard bullet used is 1.000.
The below statements are not all there is to BCs. rather, the info below is BC in its most simple state used for comparison purposes to show the relation between sectional density and BC.
BC is (for the most part) a simple function of Sectional Density and Form Factor.
SD = Bullet weight (in pounds) / bullet diameter^2
BC = SD / FF
Change the SD and not the FF and you change the BC plain and simple.
Bullet length with a specific form factor made of a material that has a given specific gravity will make up it's weight. Make it longer and the BC goes up due to the added weight and subsequent SD. When we take two different bullets of equal weight and equal form yet one is a smaller caliber such as in the case of a 180 30 cal and a 180 284 cal the smaller caliber will always yeild a higher BC. This is because the weight to caliber ratio offers a much greater sectional density. Remember, increase the SD and the BC goes up all other components being equal. The side effect is that the bullet with the smaller diameter will be that it will be longer. This is partly where the idea comes from that longer bullets have higher BC's.
Two bullets of identical demensions where one is made of aluminum (specific gravity of 2.69) and the other is tungsten (specific gravity of 19.62) the tungsten will have a MUCH higher BC. If you have a jacketed lead bullet and an all copper bullet of identical demensions, again the jacketed lead bullet has a higher BC. You could have an aluminum bullet twice as long as a tungsten bullet utilizing the same form and the tungstun bullet will still win. It would take an aluminum bullet 7.3 times longer than a tungsten bullet to surpass the BC of the tungsten bullet. So if a bullet made of tungsten was 1" long, it would take an aluminum bullet of 7.3" to surpass the BC of the 1" tungsten bullet.
Regardless of how long the bullet is, bullet length in and of its self does not equate to a higher BC.
Granted there will be other factors at play where the BC is concerned such as bore quality, velocity, stability factor etc.........The above is geared towards the basic mathematical components where all other factors such as bore quality, velocity etc.... are equal. Also it should be noted that the above statements are based on the G1 drag model. It is somewhat difficult to compare ballistic properties of different bullets if the BCs are refering to different drag models. With all the computers in the world, as powerfull as they are and what knowledge of mathematics we have, there is no substitute for measuring BC accurately without firing tests. Be it doppler, TOF (by way of bullet activated relays), double chronies, or drop tests. We can predict them with a reasonable degree of accuracy. Accurate enough to get on a big peice of paper anyway to be fine tuned.
So in short, in a sense, bullet length has alot to do with a bullet's BC but not in and of its self. Only how it relates to the overall bullet weight which in turn gives life to the SD.
Clear as mud??
As far as accuracy, the theory is that they have better accuracy potential due to having no jacket concentricty issues. The fact is that most decent manufactures have pretty high tolerences so I cannot say it is entirely true but I guess it makes sense. I have found mono metals to be quite finicky albiet I have not worked with them as much as I should. I know plenty shooters that use them with great accuracy results. Personally I think it boils down to using the right twist for the right bullet. That said, it applies to both mono metal and jacketed lead.
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Last edited by Michael Eichele; 02-12-2011 at 05:06 PM..