Bullet making for more speed and better BC

[3gunF1guy]

I know just enough about bullet making to be dangerous, and I have a question.

For instance Burger bullets are made using J4 jackets, they then use lead wire, cut to a specific length, then formed in a die. The lead is then pushed into the jacket at a high pressure. The bullet is then formed in a series of dies to shape it for size and to close the point of the bullets. Pure lead is usually used in the making of the bullet. (I think??)

I shoot the 140gr 6.5 cal VLD bullets with a G7 bc of .303, The 120 gr match has a bc of .232.

Why don’t bullet manufactures mix tin with the lead to lower the density and use the 140 dies to make a 120gr bullet with the 140 bc. Tin is about 64 percent less dense (455.67 lb per sq foot) than lead (707.96 lb per sq foot) and on the Mohs scale of hardness of metal, it has the same hardness as lead (Mohs 1.5)

In my 6.5 CM a 140 going 2800 fps has a drop of 32.63 moa (341.69 inches) and 6.18 moa (64.68 inches) of windage with a 10 mph wind, at 1000 yds.

A 120 gr bullet with the same bc and shot at 3000 fps would give a drop of 27.96 (292.83 Inches) and 5.51 (57.74 inches) of windage.

 

[FCS]

You would want to go the other way, increase density to improve BC. Reducing density, having same cross sectional area for wind to push on is counter productive and is going to be lowering your BC.

 

[Milo 2.5]

I bet cost comes into play also. Waterfowl shotgun loads, Tungsten, even steel compared to lead?

 

[Greg Langelius *]

I don't know and I think it's an interesting question.

My initial response would be that bullet makers are very good at what they do, and generally have very sound reasons for their decisions.

My second response would be that live performances tell us more than calculations to multiple decimal paces; there are a lot of small variables out in the shooting environment that add up/cancel out, and are well beyond the reach of either the shooter or bullet makers to have direct influence upon.

Finally, the kind of weight/BC relationship you suggest is probably to be found more easily by working with solid copper bullets. Always base your bullets selection with an eye to twist rates, which are based on bullet length, and not on bullet weights.

This question is probably better addressed to the bullet makers themselves. The have tech support folks who have probably seen this question before. If you get a better answer, please share it with us.

Greg

 

[TimeWillTell]

Don't forget that the bullet weight is taken into account in the calculation for BC. So lowing the density of the core material will result in the same form factor of the projectile but because the weight is reduced you will have a lower BC. FCS is correct in his point that you would want to use a more dense core material in the same form factor.

When looking at form factor and comparing the 155 berger hybrid vs the 185 berger hybrid, the 155 hybrid has a lower form factor (0.945) than the 185 hybrid (0.958). Lower is better when looking at form factors so the 155 hybrid actually has less drag than the 185. So if you could make the 155 hybrid the same shape as the 155 hybrid but make it weight the same as the 185 hybrid, then you would be onto something. This, however, will require a metal such as tungsten to accomplish and be prohibitively expensive.

Read Bryan Litz's book Applied Ballistics. Very informative.

 

[DAVETOOLEY]

Depleted uranium cores work as well but that's another story.

 

[Bear24]

I'm no expert by any means but there are limitations on every caliber of bullets

if you take a 140g hybrid and keep the same exact outside dimensions but drop the density down to 120g you have decreased the BC of the bullet.

Density has a large effect on the BC as does the dimensions of the bullet. Lighter weight bullets lose speed at a faster rate than heavier projectiles and also get pushed by side forces easier considering the same surface area.

This is just my understanding, Litz may chime in and blow my theory out of the water

 

[blackfoot]

Look at JLK website. The do exactly what you are talking about with some of their bullets. The 6.5 130 and the 6.5 140, for instance, have the same dimensions made in the same die, with a different weight core. BC is lower on the lower weight bullet.

 

[pawprint2]

I'm no expert by any means but there are limitations on every caliber of bullets

if you take a 140g hybrid and keep the same exact outside dimensions but drop the density down to 120g you have decreased the BC of the bullet.

Density has a large effect on the BC as does the dimensions of the bullet. This is just my understanding, Litz may chime in and blow my theory out of the water

^^^^^
This is right on, I believe in this case, you would lower the BC by around 14-15%, increase the cost, because of several factors, the cost of material, the cost of the higher temps used in the melting of lead and tin, harder core requires more work to shape.
I do take exception with the statement, "Lighter weight bullets lose speed at a faster rate than heavier projectiles and also get pushed by side forces easier considering the same surface area." This just is not true. One only need to look at BC tables of bullets, lighter bullets with a better design, often have a higher BC than a heavier bullet. Bullet "tipping" can improve BC without changing the weight at all, in fact if one trims the meplat, prior to trimming, not only will the weight go down (the amount trimmed) but the BC will go up. The smaller the caliber, generally speaking, the greater the effect. But with all that said, Bear24 is right on regarding the reduction in weight, without any other modifications to the size/shape of the projectile. There is some good evidence that a harder core, generally delivers a more consistent group (accuracy) but to quantify the hardness would require great bullet companies such as Sierra to divulge their exact formulations, you know the MK line has a very hard core-antimony or like is added to the lead.

 

[bax]

I don't know how Berger does it. I make 6mm bullets using the technique that the OP described. There is a certain amount of force required to squirt cores, seat cores, and point up the bullets. The squirt die is nothing special but the seater punch is sized to a tenth so that the lead doesn't squeeze between the punch and the tapered jackets.

If I recall correctly, adding tin to the lead makes it harder and less ductile and that would change the amount of force required to make the bullet. I would have to apply a lot more force to insure that the core was completely seated into the bottom of the jacket. Because of their shape, my existing core seat punches are probably not strong enough to work with a material that is harder than straight lead. I would also question the strength of the punch I use in my point-up die.

It is not clear to me that you could change the bullet core material without re-engineering the dies, presses, and maybe the jackets. For every problem there may be a solution but I think that describes the problem for the custom hand-made bullet crowd.

 

[gewehr]

I thought most bullet cores were a lead antimony alloy


Sent from my iPhone using Tapatalk

 

[pawprint2]

I don't know about every bullet company, but Sierra publishes 5 different cores, 4 of which are alloys: 6%antimony-4%tin/6%antimony/3%antimony/1.5%antimony and pure lead.

 

[3gunF1guy]

I'm fairly sure that the BC is strictly a function of how aerodynamic the bullet. Isn't the BC the same as the Coefficient of Drag???

If I use the same bc and just change the weight of the bullets, I get, with my gun, about 50" less drop at 1000yds. The wind is close to the same, about 7" of drift less.

If I am wrong about the BC and the CD then maybe we can change this thread into how the BC works and the relationship between weight, aerodynamic drag, drop and wind calculations.
Unless I need to hire Adrian Newey to explain it to me.

 

[Bear24]

I'm fairly sure that the BC is strictly a function of how aerodynamic the bullet. Isn't the BC the same as the Coefficient of Drag???

If I use the same bc and just change the weight of the bullets, I get, with my gun, about 50" less drop at 1000yds. The wind is close to the same, about 7" of drift less.

If I am wrong about the BC and the CD then maybe we can change this thread into how the BC works and the relationship between weight, aerodynamic drag, drop and wind calculations.
Unless I need to hire Adrian Newey to explain it to me.

No, the BC is a function of mass, diameter, and Drag coefficient.

BC= mass/diameter^2 * coefficient of form

 

[pawprint2]

I'm fairly sure that the BC is strictly a function of how aerodynamic the bullet. Isn't the BC the same as the Coefficient of Drag???

If I use the same bc and just change the weight of the bullets, I get, with my gun, about 50" less drop at 1000yds. The wind is close to the same, about 7" of drift less.

If I am wrong about the BC and the CD then maybe we can change this thread into how the BC works and the relationship between weight, aerodynamic drag, drop and wind calculations.
Unless I need to hire Adrian Newey to explain it to me.

Sir, I don't believe you've "got a handle on it", as BC is not a static number or property but changes with velocity, I don't believe you can give an example of two identical BC bullets with different weights, that exhibit 50" less drop at 1000 yards given the same start velocity. You're not taking into consideration the continuous change in BC, along with the continuous change in velocity. Sierra has published some really good info on BC in their 5th Edition loading manual (and I'm sure in many other spots), in fact they have dedicated an entire chapter to the subject, the Doppler radar measurements, as they relate to BC are particularly interesting.