Advancements in bullet design...

[Fig]

...are all moving towards one thing. Setting aside all terminal ballistics, and only focusing on flight:
Bullet designs have gotten incrementally better since I started shooting in the 1970s. New bullets come out with a slightly higher BC. Yet...

The physics is the physics. We have known, both theoretically/mathematically on paper and through testing, what shape has the lowest drag coefficient and therefore the highest BC since 1947. The Sears-Haack body is the shape of an object with the lowest possible fluid drag.

The more a bullet looks like that the higher BC it's going to have and the slower the delta of speed as drag acts on it as it moves through air. There simply AREN'T "advancements" in bullet design when the most efficient shape possible has been around for 75+ years. Yea, there are materials, bonding, etc., but none of that is going to make it fly any better. Why isn't there a VLD that is literally a Sears-Haack body? Why isn't every competition bullet a Sears-Haack body? Is the symmetrical ogive at the rear some manufacturing or reloading problem? Am I missing something obvious? Really, as I look at the progression of bullets I've used I can literally see them getting more and more like a Sears-Haack. Is there something stopping us from just going directly to it? Is it too costly, or is it not possible to point both ends? I mean, there must be some valid reason I'm missing, because it's not like the best possible shape is a secret. Hell, if it is some manufacturing process problem then why not just weld two flat back bullets together? There is always going to be a market for the best, and we have always known exactly what that is.

Is someone somewhere crafting these for their own use? People are turning monolithic bullets, but I haven't seen one that was literally a Sears-Haack. Why, or are they out there?

Maybe this whole line of thinking is dumb, I don't know, but I've seen a thousand posts about a new bullet design, when there's really only a single one, and every bullet that doesn't care about terminal ballistics wants to be that one design.

​

 

[diggler1833]

Man, imagine the case capacity something like that would eat up. Not to mention that you'd probably run into magazine length restrictions.

I'm sure that there are more factors that the engineers can detail.

 

[rlsmith1]

I would guess stability is an issue and the rear facing "point," or whatever the scientific term is for it, would get deformed under pressure at ignition. Boat tails try to do this to a degree and I'd be interested if boat tails are 10% or 80% effective compared to the image above.

Hornady has stated as well that a benefit of the ATIP is more consistency with the really pointed bullets and they actually reduced the "pointiness" to gain consistency. I'm sure a bullet like that would have to be turned

 

[Supersubes]

Without some fancy sabot, I dont see how the shape would work in our current cartridges. Seems it would also take some incredible twist rate despite having very little bearing surface.


It would be interesting to see how it would scale for an actual benefit. For example, is the BC so good that it could be a 80 grain 6.5 and outperform a berger 156 at the same velocity? Or is the reality that its 10% better, and the challenges with loading and shooting it far outweigh the small advantage?


I didn’t stay in a holiday in express last night.

 

[Macht]

In-bore tilt would be obscene, CG location is also not doing you any favors. Low drag doesn't mean it will shoot small groups.

ETA: Thinking further, the CG location isn't a help but the extreme projectile length is even worse.

 

[Fig]

I get what you're saying, but how far off are modern competition bullets really? I mean, they're getting there...slowly. Every new bullet design for BC and flight characteristics is moving one direction, to one design. It's the design that physics determines is the best one.

It is the vaccum created by the air behind the flat surface at the rear of the body that causes the most drag. It's also what disturbs the air the most and causes light to refract when you see trace. This is what is literally pulling backwards on the bullet like one foot on the gas and one foot on the brake. While this would look like a big jump back in the day, it seems like we're almost there now. The Sears-Haack brings the molecules sliding along it's surface back together at the rear eliminating this vacuum as much as possible.

I am not a physicists or a bullet manufacturer. The actual equations involved may as well be Chinese to me, but I am literate, and grasp the concepts, and can certainly see what the body looks like and why it is the most efficient.

The case capacity argument seems moot to me with the short/fat cases with long necks that we now have, and the VLDs protruding into them with no ill effect. I don't think a longer neck to contain the body is a deal killer. Yes, you will probably get less life out of your cases, but I'll bet every single ELR shooter (and most LR steel shooters) wouldn't care.

I also don't believe that the tapered back is going to deform in a barrel. From my experience the only part of a bullet that deforms prior to impact is bearing surface which contacts the lands to impart spin. Once the bearing surface makes contact there is an effective seal. The explosion behind it doesn't care what shape it's imparting the force to as long as it's not escaping along the bearing surface. I don't see why eliminating the heel and base of the bullet would have any effect.

Maybe I'm wrong, but that's how it seems to me.

 

[Fig]

Just eliminating the base and turning it into a point rather than a flat would be the next logical progression, and I'll bet would significantly advance the BC. No, it's still not the actual SH body, but it's a jump closer.

In-bore tilt would be obscene, CG location is also not doing you any favors. Low drag doesn't mean it will shoot small groups.

Again, it's all been moving this direction and while maybe not practical for a true SH Body, straightening out the ogive to have a longer bearing surface doesn't seem like it would have a huge effect (the exact design we have now), but why a flat back? Why not point the back to get closer to the ideal? Why the incrementalism? Bullets are one use. It's not like you can get our customers on the refill cartridges or upgrades. There doesn't seem to be any fiscal purpose for a bullet manufacturer not to try and get as close as practical. Are there bullets available with a pointed base (no base)? Isn't that the next step of "bullet advancement" or rather closer to the ideal of SH Body?

Is center of gravity in the center of the bullet a bad thing? Is it possible that with much less drag and little or no vacuum behind the bullet it would require LESS spin to stabilize? Where is the CG on modern LVDs? I'm asking...

 

[Fig]

With all the Ballistics experts on this site this is all I get.

 

[Tokay444]

Any twin spindle Swiss turning machine could crank that shape out of copper solid en masse.

 

[6.5SH]

Just eliminating the base and turning it into a point rather than a flat would be the next logical progression, and I'll bet would significantly advance the BC. No, it's still not the actual SH body, but it's a jump closer.

Again, it's all been moving this direction and while maybe not practical for a true SH Body, straightening out the ogive to have a longer bearing surface doesn't seem like it would have a huge effect (the exact design we have now), but why a flat back? Why not point the back to get closer to the ideal? Why the incrementalism? Bullets are one use. It's not like you can get our customers on the refill cartridges or upgrades. There doesn't seem to be any fiscal purpose for a bullet manufacturer not to try and get as close as practical. Are there bullets available with a pointed base (no base)? Isn't that the next step of "bullet advancement" or rather closer to the ideal of SH Body?

Is center of gravity in the center of the bullet a bad thing? Is it possible that with much less drag and little or no vacuum behind the bullet it would require LESS spin to stabilize? Where is the CG on modern LVDs? I'm asking...

Spend the ~$10 for this eBook:

https://www.amazon.com/Ammunition-Demystified-Bubbas-Guide-Really-ebook/dp/B09YWDB1NW

 

[Fig]

I will get it.
Have you read it?
Does it talk about this or the reasons bullets must have a flat back?

 

[Tokay444]

I get what you're saying, but how far off are modern competition bullets really? I mean, they're getting there...slowly. Every new bullet design for BC and flight characteristics is moving one direction, to one design. It's the design that physics determines is the best one.
View attachment 8592550View attachment 8592552View attachment 8592557
It is the vaccum created by the air behind the flat surface at the rear of the body that causes the most drag. It's also what disturbs the air the most and causes light to refract when you see trace. This is what is literally pulling backwards on the bullet like one foot on the gas and one foot on the brake. While this would look like a big jump back in the day, it seems like we're almost there now. The Sears-Haack brings the molecules sliding along it's surface back together at the rear eliminating this vacuum as much as possible.

I am not a physicists or a bullet manufacturer. The actual equations involved may as well be Chinese to me, but I am literate, and grasp the concepts, and can certainly see what the body looks like and why it is the most efficient.

The case capacity argument seems moot to me with the short/fat cases with long necks that we now have, and the VLDs protruding into them with no ill effect. I don't think a longer neck to contain the body is a deal killer. Yes, you will probably get less life out of your cases, but I'll bet every single ELR shooter (and most LR steel shooters) wouldn't care.

I also don't believe that the tapered back is going to deform in a barrel. From my experience the only part of a bullet that deforms prior to impact is bearing surface which contacts the lands to impart spin. Once the bearing surface makes contact there is an effective seal. The explosion behind it doesn't care what shape it's imparting the force to as long as it's not escaping along the bearing surface. I don't see why eliminating the heel and base of the bullet would have any effect.

Maybe I'm wrong, but that's how it seems to me.

Pressure in a fluid is exerted at right angles. That's a large part of why bullets have flat bases. While the pressure building behind the SH shape will eventually move it out of the barrel, I don't think that acceleration will be nearly as efficient as with a perpendicular surface to push against.

 

[6.5SH]

I will get it.
Have you read it?
Does it talk about this or the reasons bullets must have a flat back?

It discusses all of the common designs and even theoretical. Also quite a bit about sabots which such a design would require.
Some of the bullet points (Har!) have been touched on here but it has more to it that is way too long to type out. The number of interactions and design compromises required for a bullet to work well are staggering, it is amazing that much works as well as it does.

 

[Fig]

Pressure in a fluid is exerted at right angles. That's a large part of why bullets have flat bases. While the pressure building behind the SH shape will eventually move it out of the barrel, I don't think that acceleration will be nearly as efficient as with a perpendicular surface to push against.

I see your point. I somewhat agree, and I think there might be some sort of measurable change in terms of efficiency, but Pascal's Law also states that the pressure is uniform throughout and exerts the exact same pressure at right angles everywhere. There is nowhere for the pressure to go in a barrel except to move the projectile down the barrel. The pressure acting at a right angle to the bullet does not rise any more than it does where the bearing surface meets the lands, because it is uniform and moves the bullet forward to relieve the pressure as the path of least resistance (by a wide margin). The same charge in a .50 round ball ML gives me almost the same velocity with a 270gr, flat back Mine Ball. I'm sure there's a difference in efficiency, but it is not enough to notice without special equipment. I don't notice it when shooting ML. What I do notice is how much a round ball sucks, and how a 270gr, .50 round ball leaving the barrel at 1,700fps looses half it's velocity and goes sub-sonic at less than 100 yards. The explosion does not seem to effect the back of a round ball bullet much at all even though the only place the pressure is acting at a pure right angle is the point on the bullet closest to the breach. Even the soft lead is not deformed or altered discernably, as the path of least resistance is to force the bullet down the barrel by an extremely wide margin. If the bullet was a cylinder, with a perfect flat back, I expect there would be no discernable of observable difference either without special equipment.

The pressure on the parts of the bullet behind the sealed bearing surface are not going compress or deform. If this were otherwise it would deform the boat tail and the heel (all receiving the same force as the base) on a flat back VLD bullet, but it doesn't. I would think that whatever the change was it could be compensated for with either a reduced or increased charge depending on which way it went. There would be no reason to try and increase the pressure of a bullet not disposed to slow down because of the vacuum behind it, and I would think you could run lower and slower and stay super sonic for far, far longer distance.

 

[Ledzep]

TLDR: Most things that you do to reduce drag cause accuracy issues either out of the gate or down range. Manufacturing slowly gets better and better and allows us to "get away with" more and still have the bullets shoot but that projectile would be extremely erratic for a number of reasons.

1. Tangent radius transition into a boat tail, and radius "ogive" boat tails have been tried. Magnus moment eats your lunch and you lose dynamic stability at long range much sooner than the potential drag benefits gain you anything. In other words, traditional boat tails are better.

2. The drag benefit per unit of length of boat tail diminishes beyond about 1 caliber. Most boat tails are 0.6-0.8 calibers long. McCoy has this in his book with drag vs. BT angle and drag vs. BT length charts. It's a "juice ain't worth the squeeze" situation.

2.5. This projectile would have to be machined/turned. Probably out of copper or you could do a two piece part out of something like tungsten with a copper band. It's not commercially viable out of tungsten (AP and they'd be $40-60 ea.). Have someone turn some out of copper and try it. In the scheme of things these would cost a barrel and a few hundred dollars extra to prove it doesn't work This shape or anything approximating it would be abhorrent to make as a cup&core bullet if you wanted to do it with consistency/precision in mind. The length of it would necessitate twist rates that will exacerbate any manufacturing flaws (eccentric mass).

3. DVRT. Low drag is nice, and going to a needle point is going to produce low drag. In a wind tunnel or in a simulation where you can force the AoA with the oncoming flow to be zero, it's all hunky dory. When you spin stabilize a projectile in the real world through pockets of variable density and variable speed/direction air and yaw & precession you are better off to compromise some of that drag reduction for increased consistency in drag for the sake of hit probability.

4. Long skinny projectiles with no bearing surface like that when subjected to a 55-80ksi kick in the ass tend not to enter the rifling perfectly straight. A guy would want more bearing surface. Also the body made of real materials is not rigid and you run into harmonic responses that do all sorts of cool erratic stuff.

 

[Ledzep]

Unfortunately these are no longer in production because I wanted to shoot them on radar but my guess is very high drag variability and dynamic instability once the trajectory arcs over and starts seeing high AoA