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Discussion Starter · #1 ·
This may be a stupid question, but what the hay. I'm curious about ballistics and started wondering about something. If longer bullets are better for ballistic stability, why not just make bullets longer.

For instance, what would happen if a 55gr .223 bullet could be made longer (not actually stretched of course) but perhaps cast into a longer jacket with a lighter lead alloy. In theory, you'd end up with the same weight but also a projectile with a better BC.

I tried searching about this concept but found nothing, which suggests this is an incredibly stupid idea or just nobody has though of it yet. Probably the former but I am naturally curious so I had to ask.
 

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Don't forget

Don't forget boat tail bullets. That is the way to make longer projectiles as that cuts down on the total weight. IMHO:confused: join the crowd.
 

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The longer the bullet the less case capacity you have for powder. Eventually you get to a point where velocity starts to drop or pressure starts to rise. Longer bullets also need a faster twist rate to keep them stabilized. A longer bullet that weighs the same will also have less wounding characteristics because the increased surface area makes them penetrate less. The smaller and more dense projectiles get more penetration. That's not to say there wouldn't be some advantages to having a bullet that's longer, but those advantages can only go so far before they become a disadvantage.
 

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Discussion Starter · #5 ·
The longer the bullet the less case capacity you have for powder. Eventually you get to a point where velocity starts to drop or pressure starts to rise. Longer bullets also need a faster twist rate to keep them stabilized. A longer bullet that weighs the same will also have less wounding characteristics because the increased surface area makes them penetrate less. The smaller and more dense projectiles get more penetration. That's not to say there wouldn't be some advantages to having a bullet that's longer, but those advantages can only go so far before they become a disadvantage.
Bullets up to, and beyond, 80gr have been stuffed into a 223 case. That's pretty heavy and long. If there's room in the case for enough powder to push an 80gr bullet, there should be plenty of room for a somewhat longer, though comparably lighter 55gr bullet.

I agree that the longer heavier bullets require a faster twist, but my question is this. What would happen if a 55gr bullet, made from a lighter alloy were produced in a length about the same as a standard 68 or 69gr bullet. Forget about stopping of killing power, for the sake of this argument, it is irrelevant.

I'm not sure I agree that projectiles of equal weight (mass) but different lengths would have dissimilar penetration. If the velocity and weight of the mass are equal, the energy should also be equal. There would be a difference in drag for sure, maybe that's the reason 55gr bullets are not longer. Perhaps they'd loose velocity too quickly.

I dunno <scratching head>
 

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Bullets up to, and beyond, 80gr have been stuffed into a 223 case. That's pretty heavy and long. If there's room in the case for enough powder to push an 80gr bullet, there should be plenty of room for a somewhat longer, though comparably lighter 55gr bullet.

I agree that the longer heavier bullets require a faster twist, but my question is this. What would happen if a 55gr bullet, made from a lighter alloy were produced in a length about the same as a standard 68 or 69gr bullet. Forget about stopping of killing power, for the sake of this argument, it is irrelevant.

I'm not sure I agree that projectiles of equal weight (mass) but different lengths would have dissimilar penetration. If the velocity and weight of the mass are equal, the energy should also be equal. There would be a difference in drag for sure, maybe that's the reason 55gr bullets are not longer. Perhaps they'd loose velocity too quickly.

I dunno <scratching head>
Longer bullets tend to tumble in flesh and that added length without added weight is what would increase the drag and make less penetration.

The advantages to having a longer bullet as opposed to having a wider bullet is that they slip through the air better. It's called the ballistic coefficient. However if the bullet hasn't gained any weight and only has gained length that will make it more susceptible to wind drift because the surface area on the sides has increased without increasing the weight which means you would be defeating the purpose of having the longer bullet in the 1st place. The extra mass of a 68 grain bullet gives it the longer range and lowers the wind drift effect upon it. A 55 grain bullet that is the same length of the 68 grain bullet will not have as much range and will be effected by wind drift more than just using the 68 grain bullet in the first place. Efficiency of powder usage would also be higher with the 68 grain bullet because it requires less powder than a lighter 55 grain bullet.
 

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Ballistics is all a trade off. If you take something in one place you lose something in another. A long light bullet would need a faster twist to stabilize, require either deeper seating or longer throat, etc. etc. The term sectional density is in simple terms weight in relation to length. The higher a sectional density number the better penetration a bullets gets within the parameters of how the bullet expands. While the long light idea in theory seems like a solution it trades other attributes of ballistics to reach the goal. So it boils down to what you want to gain versus what you will lose.

The 55 grain bullet in the 223 was used originally as the first rifles had a much slower twist than used these days. It think they were either 1/12 or 1/14. Bullets at 55 grains were marginally stable. This gave the 223/5.56 the reputation for bullets tumbling. Twists were tightened up over time to the 1/7 and1/8 common today to stabilize heavier longer bullets. It would be possible to make a long light bullet and make it stable but it would not behave on impact the same as heavier similar length bullets.

Ballistics scientists have been struggling with these problems for years in calibers from 5.56 to 240mm. There is no perfect projectile.
 

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Voluntaryism and twodog max are right on target .... a bullet's ability to overcome air friction (ballistic coefficient) is based on three things ... its diameter, aerodynamic design, mass, and length. When a bullet has a given diameter (ie .224"), about the only way to make it longer is to make it heavier (or vise versa). Terminal ballistics depend on just two parameters ... weight and velocity so weight is a common factor for both external ballistics and terminal ballistics.

Here's a good analogy about weight using shotgun shells as an example. In years past, lead shot was used in nearly all shotgun shells because lead pellets retained velocity better than any other conventional metals ... plus it was cheap. The size of the pellets were changed for shooting at different distances ... ie larger diameter pellets for longer shooting distances because heavier pellets would carry farther ... meaning they retained more velocity and energy than lighter pellets. In more recent years, lead was found to be toxic so other materials are now used such as steel or bismuth. As I recall, a steel pellet is about half as heavy as a lead pellet of the same size. Both are round so their aerodynamic qualities would be the same. So here's the test .... shoot a shotgun and chronograph lead pellets versus the same size steel pellets at a normal bird hunting range of 30 yards. Here's what you will find ... if the muzzle velocity was the same, the lead pellets will clock much higher velocities than the same sized steel pellets. Both will be affected by gravity at the same rate of 32 ft/sec/sec however because the lighter steel pellet looses so much velocity, its time of flight is longer to travel 30 yards, which in turn makes it drop several more inches than a lead pellet of the same diameter. Further, weight not only affects aerodynamic properties, it also affects terminal ballistics so when a steel shot hits a duck at 30 yards, chances are it won't have enough momentum to penetrate and will literally bounce off. A lead pellet will penetrate deep enough to kill the duck. So ... the results are: a heavier lead pellet will have considerably more retained velocity at a distance of 30 yards, it takes less time to get to the target, it doesn't drop as much, and it penetrates deeper.

Let's apply the above paragraph to bullets. Heavier bullets of the same diameter will retain more downrange velocity ... just like a lead pellet versus a steel pellet as noted above. Ballistic coefficient comes into play with rifle bullets because it has a direct influence on the bullet's ability to deal with air friction that really makes a significant difference at longer distances. For handgun bullets where the typical shooting distance is 50 yards or less (25 yards is normal), the bullet's ballistic coefficient is not very important. Yes, a wad cutter will drop more than a round nose bullet but who cares ... both will still make it to the target with enough energy to do the job. For rifle bullets, the ballistic coefficient has a dramatic affect on velocity retention, bullet drop, and wind drift. When ballistic coefficient formulas were devised, a BC of 1 meant the bullet was perfect and presented no resistance to air (impossible). A decent 7mm bullet may have a BC of .600 or more. A .224" bullet typically has a BC of .300 or less. The longest and heaviest .224" bullet I could find is a 80gr Hornady A-Max and has a BC of .435. As you can see, the best .224" bullet doesn't come close to a larger diameter bullet.

If you could stretch a 55gr bullet to make it longer yet maintain the diameter, what would you accomplish? The bullet mass would now be light for its volume compared to a normal bullet with the same length. This would make the bullet slow down in a shorter distance and drop considerably more than a normal bullet because it took longer to travel to the target. Basically the same as using steel shot versus lead shot. Barnes bronze bullets do exactly that ... an equal weight Barnes bullet will be notably longer than a conventional bullet with a lead core and copper/zinc alloy jacket. Assuming they both weigh the same and are driven to the same muzzle velocity, the Barnes bullet will chronograph notably slower at 200 yards, it will take longer to get there, and it will drop a few inches more. Additionally, the longer Barnes bullet requires a faster twist rate to maintain downrange stability. This make me feel sorry for California residents where bullets containing lead are prohibited.

Prior to WWII, the Army experimented with depleted uranium and found it made an excellent material for bullets ... much heavier than lead and especially useful to penetrate tank armor. It is now used in 30 mm PGU-14/B armor-piercing cartridges fired from fighter aircraft. Using depleted uranium increases mass without increasing length so the same rifling twist rate will work to keep the bullet stabilized downrange. A win/win scenario ... except for one thing ... depleted uranium is still a bit radio active ... talk about lead being toxic ... it can't hold a candle to depleted uranium.
 

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Discussion Starter · #9 ·
So, in a nut shell, a bullet can't really have too much mass, the more mass the better, and the mass density of lead is pretty much a ballistics brick wall. Longer bullets, assuming lead is used, only fly better because they have more mass. Is that about it?
 
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Very Low Drag bullets seated to a particular length will shoot well in one rifle with a particular chamber/throat, and shoot not so well in another of the same design. Very frustrating. One will like a particular distance of the bullet from the rifling, another will like a very different distance, or actually thrust into the rifling.

Berger makes a lot of VLD designs. Sierra makes a lot of much more blunt bullets, which work well in a wide variety of chamber/throat designs. Hornady is in-between: I have an M1 that won't shoot them for sour owls.

In short, if you don't read wind well but have lots of it, the VLD designs might help you a lot, if you have the time to find the 'sweet spot' distance off the lands, and track it, loading bullets longer as the throat erodes.
 

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Scorpio, Yup, you pretty much nailed it but there is one more issue. Longer rifle bullets allow for a better aerodynamic design (higher BC) yet still have enough body for a bearing surface with the bore. This is the reason why 55gr FMJs have such a poor BC ... too short. If you look at good bullet designs in a reloading manual, the ones with the highest BCs will have a long tapered nose and a significant boat tail .... not possible with a shorter (lighter) bullet. Obviously there is a bullet weight limit for any cartridge ... sometimes regulated by the length of the magazine, sometimes by rifling twist rate, but always by chamber pressure.

As for mass .... consider this. What retains the most energy when launched at the same velocity ... a 38 cal bullet or a miniature marshmallow? Yes, this is an extreme example but the concept is the same for different weight bullets ... just not quite as dramatic.
 

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Fwiw, you could compare all copper bullets of a given weight to traditional ones, and see if the BC tend to match your initial contention or the explanations given subsequently. Copper is less dense than lead.
 

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I got a couple of boxes of Barnes copper bullets along with a rifle I purchased....I was unsure of how to load for them as I've "heard stories"....Barnes has a web page available with their load data for many powders and it's handy...people that are starting to load Barnes here in California because of the moronic no lead laws need to be cautious with their loading...not a really good idea to just transfer data "weight for weight" as it might not be a good thing to do....
 

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I'll apologize for getting pretty detailed in my response below, and very long-winded. There's a lot to consider, but if you take the time to read all of this, I hope it'll illustrate at least ONE avenue that cripples this idea, without boiling the ocean for ALL avenues.

I'll run through all of the detail below, but the bottom line ends up at this:

You won't gain as much as you're thinking in trajectory advantage. If I stretch out a .223remington with 50grn V-max to the same shape of a 75grn A-max but keep it at 50grns, I end up with 10" MORE DROP at 500yrds compared to a standard 50grn V-max AND it has the same drop (coincidentally) as a standard 75grn at 500yrds!!!

If longer bullets are better for ballistic stability, why not just make bullets longer.

For instance, what would happen if a 55gr .223 bullet could be made longer (not actually stretched of course) but perhaps cast into a longer jacket with a lighter lead alloy. In theory, you'd end up with the same weight but also a projectile with a better BC.
The simplest answer here is that the bolded statement above is not correct - longer bullets are less "stable" than short bullets. Long bullets need more spin to stabilize than short bullet. BUT, your second statement, underlined above, is correct, but the advantage isn't there - which I'll discuss below.

Longer bullets - in general - have better aerodynamics, NOT better "ballistic stability."

In lock step with that, there are physical real world limitations that come into play, just a few of which I'd list below:

  • Chamber throat length and bullet jump
  • Magazine length
  • Case capacity
  • Bullet ogive length vs. bearing surface for rifling contact
  • Barrel twist rate
  • Barrel length and muzzle velocity
  • Penetration will be decreased compared to its bullet form (lower SD for size

Discussing each of these topics could be equally long-winded posts, but the short version is that there's a LOT going on that can't be ignored when you talk about changing a bullet profile and density.

So let's do a little exploring down one of those rabbit holes: I shoot a lot of 50grn Hornady V-max's, and a lot of 75grn Hornady A-max's in 22caliber. What would happen if I took a 50grn V-max and stretched it out with an appropriate alloy density change to make it look like a 75grn A-max?

I can look at it two ways - either I'm growing a V-max, or I'm lightening up an A-max. If I stretch the 50grn, that'd grow a 0.7770" bullet up to 1.1210" and change my BC from 0.242, upward - it would not be the same 0.435 BC as the 75grn V-max because that bullet doesn't have the same sectional density.

But that's easily calculated - the 75grn A-max has a BC of 0.435, with a sectional density of 0.214. Since BC = SD/i, where "i" is a form factor (not a drag coefficient, but related). For that particular bullet, if .435 = .214/i, then i = .214/.435, so the form factor for the SHAPE of the 75grn A-max is 0.492. It's easy to calculate from there what BC would be for the 50grn version of the same bullet shape: 0.224" 50grn bullet, SD = 0.142. 0.142/0.492 = 0.289

SO - if I stretch a 50grn V-max out to be the same shape as a 75grn A-max, I'd only increase my ballistic coefficient from 0.242 to 0.289!!! Reminding, that's compared to the 75grn A-max of the SAME SHAPE of 0.435!!!

And that doesn't even take into account that my stainless AR mags only let me fit 2.30" at max, and Hornady recommends 2.2390" COAL. Seated to the same length, there's 0.344" MORE BULLET taking up space in the case, meaning I have less powder capacity and/or higher chamber pressure. So when I run out that difference (indulge me the differential of a flat base vs. a boattail), that comes up to a lost capacity of 3 1/3grn of H2O.

So out of a ~30grn H2O case (.223rem), I'd give up 11% in powder capacity. Instead of packing 27.0grn of powder behind a 50grn V-max, now I'm losing almost 3grns of powder, and the 3,200fps that I'm able to hit today drops off to about 2,850-2,900fps, which was the starting load I used to develop my current V-max load - and not coincidentally - about the same as a MAX LOAD for the 75grn A-max.

Just for fun, run that through the Greenhill twist formula - a 50grn V-max at 0.7770" and using a generic 10.9 specific gravity at 3,200fps, I'll stabilize comfortably in a 1:12" barrel, whereas if I run that bullet out at 2,900fps at 1.121", now I need a 1:8" twist to stabilize it. That kinda kills anybody with a DPMS, Bushmaster, Rock River, Savage, Remington, Ruger Hawkeye (not American), and many other models that come with 1:9" or 1:12" barrels - especially if you start talking about a 16" AR carbine that would only get about 2,550-2600fps with such a bullet.

What does that mean at the range? Punch in the numbers for a 50grn bullet with a BC of .242 running 3,200fps against a 50grn bullet with a BC of 0.289 running 2,900fps... The standard V-max at 3200fps would have 8" LESS DROP than a slightly more aerodynamic "low density" 50grn bullet at 2,900fps, which is coincidentally the same exact drop I get for a 75grn Amax at 500yrds running 2650fps. I show 82" of total drop for the 50grn LONG bullet, 74" for the 50grn V-max, and 84" for the 75grn A-max.

So - quick recap - you stretch out a 50grn v-max to the same size as a 75grn A-max:

  1. I only gain very slight BC improvement 0.242 becomes 0.289
  2. I lose ~300fps due to powder capacity loss from deep seating long bullets
  3. I need a 1:8" or 1:7" barrel just to stabilize a 50grn bullet
  4. There's no difference in 500yrd total drop compared to a 75grn bullet, even though the 75grn bullet is running even slower (higher BC)
  5. I drop 10" MORE with the "more aerodynamic" low density 50grn bullet than a standard 50grn bullet, and the exact same drop as a heavier 75grn bullet at 500yrds.
  6. Bottom line - I did a lot of work and didn't get any advantage for my trajectory
 

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If things were easy, they would already have been done.
If only one variable mattered, they would already have been done.
You are always balancing at least four variables and often more.
No matter how hard you throw a potato chip, it still won't travel very far.
 
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