Optimal caliber for ELR?

Consensus? I do not know, but the good => better => best caliber for extreme long range is the one with the biggest diameter because the bigger diameter, the heavier projectile you can fit, and said combination will give the biggest sectional density, and thus the form factor i in the Ballistic Coefficient formula becomes less significant and forgiving:
SD = BC x i
The G1, BC is based on a theoretical one pound projectile of 100 caliber, or 1.000 inch diameter with a form factor of 1.000 and thus gives a Ballistic Coefficient of 1.000
WARNING!
math follows:
firstly, nothing up my sleeves,
SD = 1.000
mass = 1.000 pound, or 7,000 grains
caliber = 1.000 inch
form factor = 1.000
Ballistic Coefficient = 1.000
since SD = BC x I then 1.000 = 1.000 x 1.000
The closest analogy to compare such mind boggling math is to think back in the 2nd grade when you started to learn about the physics of electronic fundamentals such as Ohms Law, but not so much about Joules law, yet.
You are probably wondering why my experience and education began in the second grade? Well, which is also a deep subject, when I was in the second grade, I bent a tang on a fork 90 degrees, and I still hadn’t learned trigonometry then I stuck the bent tang into the Hot side of a wall plug and my little hand cramped down on the fork handle and I was being electrocuted. I still remember my Dad laughing then he kicked my hand off the fork and said that if we were in Europe and the Nazis didn’t kill me, the 240 volt house voltage would’ve. My Mom was so pissed at my Dad that I remember her smacking him several times as he kept laughing, and I was so proud to have a mom come to my rescue at such a young age and beating down a laughing ogre that was still laughing, until I heard my so called hero mom screaming at my Dad in cuss words and Spanish that y
he ruined her fork.
So much for hero moms.
My Dad being in WWII was a radioman and started teaching me about Electromotive force being measured in volts, intensity of electrical current being measured in amperes, and resistance being measured in ohms, and since he also doubled as a scout sniper anti-sniper hunter, my ballistics education began also.
Three variables in electronic principals E = I X-ray, and three variables in ballistic kinetic energy (Ke) = 1/2 x m x v^2.
Note that incrementing the mass only increments the kinetic energy proportionateply, but incrementing the velocity increments the Ke by the squared value proportionalply.
Now comes Joules Law: Power which is measured in Watts equals the intensity of the current that is measured in Amperes squared and multiplied by the resistance that is measured in ohms, so it looks like this:
W = I^2 x R; similar to Ke = 1/2 x m x v^2, or basically comparatively speaking:
W = Ke
v^2 = I^2
R = 1/2 x m, or m/2
Power = Dynamic Kinetic energy (there is also static potential energy as well as internal energy, calculated only).
velocity = intensity
resistance = half-mass
So, my Dad would tell me that the USS Missouri would fire two ton projectiles at just barely over the speed of sound and they would travel over the horizon, way past the line of sight of the crows nest on the ship, and hit an enemy boat about the size of a mansion, and these were of caliber, or 16, or 18 inch guns that I remember him saying.
So to answer the question?
The biggest and heaviest projectile combination, but with airguns, we need to calculate the barrel length too; as well as the molecular mass of the gas being used to transfer the momentum and kinetic energy to the projectile.
Now, keep in mind the ideal gas law does not apply to air guns as the Volume has a super script gamm function (compressibility of approximately 1.4; but closer to 1.396 according to my experiments at Normal Temp and Pressure (NTP), so at different elevations barometric pressures and temperatures your mileage will vary.
For the average mass of dry air, I use 28.966 daltons, which equates to 28.966 grams of dry air per mole; where a mole is defined as exact to be 6.02214076x10^23 entities, just like a dozen means 12, a score means 20 (“four score and seven years ago” = 1863 - 1776), a myriad means 10;000; etc. where a word means a number).
Now, we shoot lead (Pb) projectiles on average; unless you are in the state of nuts & fruits, and lead has a mass of 207.2 da, or 207.2 grams of lead contain 1 mole of lead molecules, so the ratio of dry air to lead is 207.2/28.966, or roughly 7:1.
Furthermore, the law of conservation of momentum will hold at all cost. I think it should be named the law of Marines holding their position at all cost would be more accurate.
Anyways, the limiting factor is the base area of the projectile, its mass, and the time the gas molecules can strike the base before exiting the muzzle approximately 3 calibers out where the dynamic frictional drag of the projectile against the barrel goes to zero and said energy is transferred as a jump in velocity and the more jump because of higher pressure causes less accuracy, but more power, but keeping in mind that consistency trumps accuracy at range when it comes to hunting at different ranges and environmental conditions.
I better stop here before I run out of text ink.
Thank you all for my increased knowledge from your posts because once I think I got it is when I realize how much more I need to know and how little I really know. Ignorance is bliss.
Numbers do not lie, but you can lie with numbers, and the laws of physics are not just really good ideas.
FJB Out!
I've got a headache now, thanks.😡😡
 
I've got a headache now, thanks.😡😡
This is what chatgpt did with it:

Here's a simpler version:

---

### Long-Range Shooting: Choosing the Best Caliber

When it comes to extreme long-range shooting, the best caliber is typically the one with the biggest diameter. A larger diameter allows for a heavier projectile, which increases the sectional density. This makes the form factor in the Ballistic Coefficient (BC) formula less significant:

\[ SD = BC \times i \]

For example, the G1 BC is based on a theoretical 1-pound projectile with a 1-inch diameter and a form factor of 1. This results in a BC of 1.

Here’s a simple breakdown:

1. **Sectional Density (SD)**: 1.000
2. **Mass**: 1 pound (7,000 grains)
3. **Caliber**: 1 inch
4. **Form Factor**: 1.000
5. **Ballistic Coefficient (BC)**: 1.000

Since \( SD = BC \times i \), we get \( 1.000 = 1.000 \times 1.000 \).

### Understanding the Basics: Electronics and Ballistics

To understand these concepts, think back to basic physics, like Ohm’s Law in electronics. My interest in these topics began in second grade when I got an electric shock by inserting a bent fork into a wall socket. My dad, who served in WWII as a radioman and scout sniper, taught me about electromotive force (volts), current (amperes), and resistance (ohms), along with basics of ballistics.

### Comparing Formulas

In electronics:
\[ P = I^2 \times R \]
(Power equals current squared times resistance)

In ballistics:
\[ KE = \frac{1}{2} \times m \times v^2 \]
(Kinetic energy equals half the mass times velocity squared)

Increasing the mass only proportionally increases kinetic energy, but increasing velocity has a squared impact.

### Practical Example: Naval Guns

For example, the USS Missouri fired 2-ton projectiles just over the speed of sound, using 16 to 18-inch guns, which could hit targets far beyond the horizon.

### Airgun Considerations

For airguns, consider barrel length and the molecular mass of the gas used. The ideal gas law doesn't fully apply due to variations in pressure and temperature.

The average mass of dry air is about 28.966 grams per mole. Lead, used for projectiles, has a mass of 207.2 grams per mole, roughly a 7:1 ratio compared to air.

### Final Thoughts

Remember, the law of conservation of momentum always applies. Factors like the base area of the projectile, its mass, and the time gas molecules act on it are crucial. Consistency is key for accuracy over varying ranges and conditions.

Thanks to everyone for contributing to my understanding. Numbers don’t lie, but they can be used to mislead. The laws of physics are not just good ideas—they’re fundamental truths.

---

Hope this helps!
 

When it comes to extreme long-range shooting, the best caliber is typically the one with the biggest diameter. A larger diameter allows for a heavier projectile, which increases the sectional density. …
That does not make sense. SD is the weight divided by diameter squared. Longer (not larger diameter) projectiles will have the higher sectional density.

Even though there were plenty of .357, .457, and .50 calibers present, the top 3 for the last two years at the RMAC big bore match were 7mm and .308 caliber.

There is a limit to the SD that can be adequately accommodated with a practical airgun.

“best caliber” will depend on the specific requirements.
 
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That does not make sense. SD is the weight divided by diameter squared. Longer (not larger diameter) projectiles will have the higher sectional density.

Even though there were plenty of .357, .457, and .50 calibers present, the top 3 for the last two years at the RMAC big bore match were 7mm and .308 caliber.

There is a limit to the SD that can be adequately accommodated with a practical airgun.

“best caliber” will depend on the specific requirements.
From a paper and ballistics approach it would seem the .510 would be the best...I.know the Accurate molds 625 spire point boat tail mold has a B.C of around .5... They come out 650 grains pure lead. If you can shoot around 1000 fps they are around 1000 foot pounds at 300 yards... Not bad for a airgun.... Now that's on paper....In a Texan that big .510 has so much vibrations and recoil.....I don't think it would shoot as good as.the smaller calibers in the same.frame..First it has to be accurate. Then ballistics and foot pounds.... So a .284 is a good comprise for ballistic recoil and vibrations in airgun s😁

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as Scotchmo says. BC increases significantly with bullet length not just calibers alone. Considering that the last 2 longest records were shot with .22 caliber, that also says something.
I currently see what an interesting alternative 6mm caliber is, which is something between .22 and .25.

The order of how to pick a caliber for an ELR is a combination of multiple factors where you have to consider ballistic coefficient, consistency of muzzle velocity, maximum possible muzzle velocity of a given air rifle, and overall accuracy.

If I have a high BC, but tragic consistency of muzzle velocity (example of a cast bullet or old valve airgun system) then a higher BC is useless to me as I won't hit anything.
If, on the other hand, I get a better BC due to more slug length, but too much muzzle velocity drop, then again I won't have the most accurate system I can have.
Everything is conditional on the number, not the acronym ELR.


For shooting at 500-600 yards, I can have better results with a completely different shooting setup than I would use at, say, 1000-2000 yards.
 
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I don't understand why swage airgun slugs don't have high b.C designs... To make normal vld slugs they use a solid swage lead core and pull.the jacket over...Point being you have to be able to swage a true VLD design with high BC...I understand cast slugs not the best,,but why cast designs have higher BC designs than airgun swage slugs.. Lee 230 grain .309 mold is the highest BC lead slug that can be used in a airgun... Its BC is over .6 something..
 
I don't understand why swage airgun slugs don't have high b.C designs... To make normal vld slugs they use a solid swage lead core and pull.the jacket over...Point being you have to be able to swage a true VLD design with high BC...I understand cast slugs not the best,,but why cast designs have higher BC designs than airgun swage slugs.. Lee 230 grain .309 mold is the highest BC lead slug that can be used in a airgun... Its BC is over .6 something..
To fully realize the advantages of that 230gr for ELR, I’d probably want a 1:8 twist at over 570+fpe. That’s a big ask for a .308 airgun.

I’ve gone a little less ambitious and plan on shooting 171gr .308 at 430fpe in a 1:10 twist.

So far, I prefer casting my own as there are better mold options available when looking for the optimal shape.
 
I don't understand why swage airgun slugs don't have high b.C designs... To make normal vld slugs they use a solid swage lead core and pull.the jacket over...Point being you have to be able to swage a true VLD design with high BC...I understand cast slugs not the best,,but why cast designs have higher BC designs than airgun swage slugs.. Lee 230 grain .309 mold is the highest BC lead slug that can be used in a airgun... Its BC is over .6 something..
the main reason why a jacketed brass bullet is not used is that the airgun probably wouldn't be able to fire it and if it did, the drop in velocity would be very high. Not to mention the airgun, where the slug is inserted directly into the grooves of the barrel, it would not fit there at all
 
the main reason why a jacketed brass bullet is not used is that the airgun probably wouldn't be able to fire it and if it did, the drop in velocity would be very high. Not to mention the airgun, where the slug is inserted directly into the grooves of the barrel, it would not fit there at all
no i understand that you can not use copper jacket.. My point being we should have the tech to be able to swage lead in the same designs as are powder burners. Probably more steps to do i would imagine..Your lathe turned .223 67 grain slugs are nice:)..I want try some in my new old tech Airforce Condor builds
 
no i understand that you can not use copper jacket.. My point being we should have the tech to be able to swage lead in the same designs as are powder burners. Probably more steps to do i would imagine..Your lathe turned .223 67 grain slugs are nice:)..I want try some in my new old tech Airforce Condor builds
The tech is there no doubt... if a pellet can be swaged then so can a BT HP with any other feature imagineable. Certainly a more complicated machine when compared to the ones used for the flat base slugs available everywhere.

Probably just a demand thing too... most off the shelf PCPs can't handle the weight that comes with the vld shape... no one likes shooting at 700fps. Except springer guys. 😝
 
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To fully realize the advantages of that 230gr for ELR, I’d probably want a 1:8 twist at over 570+fpe. That’s a big ask for a .308 airgun.

I’ve gone a little less ambitious and plan on shooting 171gr .308 at 430fpe in a 1:10 twist.

So far, I prefer casting my own as there are better mold options available when looking for the optimal shape.
Hi Scott,

If you don't mind sharing what were the reasons you are changing over to .308 from .284? Is one being able to see where you hit in the dirt or on the steel easier?
 
Hi Scott,

If you don't mind sharing what were the reasons you are changing over to .308 from .284? Is one being able to see where you hit in the dirt or on the steel easier?
Who said I’m “changing over”? Though I might.

I still consider my 7mm (.284) to be a better choice for current long range matches. Though anything from .257 to .308 could be really good. Part of it when doing a custom build is what you want to do and what’s available (barrels, twist rates, slugs, molds).

My .308 build is a project/study for the extreme part of airgun ELR. Where my .257 was intended as a 300yd gun, and the 7mm is a 500yd gun, this .308 is intended as a 600yd+ gun.

At 600yds+, minimum wind drift occurs at about 1050fps to 1070fps. It takes 2.5fpe/grain to get to 1060fps. Going from there guides my decisions on what could work.

It’s certainly possible to shoot well with less velocity, but I don’t consider it optimal.

For slugs/molds that are currently available, what’s the highest BC slug that can be shot at 1060fps in an airgun?

If it’s ready, even knowing the 7mm is likely “better” for EBR, I might shoot my .308 at that match.
 
Who said I’m “changing over”? Though I might.

I still consider my 7mm (.284) to be a better choice for current long range matches. Though anything from .257 to .308 could be really good. Part of it when doing a custom build is what you want to do and what’s available (barrels, twist rates, slugs, molds).

My .308 build is a project/study for the extreme part of airgun ELR. Where my .257 was intended as a 300yd gun, and the 7mm is a 500yd gun, this .308 is intended as a 600yd+ gun.

At 600yds+, minimum wind drift occurs at about 1050fps to 1070fps. It takes 2.5fpe/grain to get to 1060fps. Going from there guides my decisions on what could work.

It’s certainly possible to shoot well with less velocity, but I don’t consider it optimal.

For slugs/molds that are currently available, what’s the highest BC slug that can be shot at 1060fps in an airgun?

If it’s ready, even knowing the 7mm is likely “better” for EBR, I might shoot my .308 at that match.

I see.

I forgot but what is the BC of the .284 slug you shoot and also the BC of the 171gr 30 cal?

For ELR in the firearms world many prefer the highest BC plus using the larger calibers. A positive for the heavy bullets like say 375 cal and up is spotting misses in the dirt and seeing where on the steel you hit to make the appropriate corrections asap.

I saw a video today of a 1 mile match where competitors shooting their 6.5's couldn't see their misses so they didn't hit the 18" steel but the guys with 30's and 338's saw where their bullets landed then corrected and made hits.

I know when I've shot ELR with my 25 cal Vulcan3 it's hard to see where the slug went if there is grass but I bet with a heavier slug it'd be easier to see where they landed.
 
The G1 BC is most commonly quoted, so that’s what I use for general comparison

105gr 7mm, G1 BC=0.28
171gr .308, G1 BC=0.42

The RA4 BC is actually a better drag model for high subsonic. So that’s what I use in Strelok.

105gr 7mm, RA4 BC=0.22
171gr .308, RA4 BC=0.32

I wouldn’t choose a heavier projectile for that reason (seeing misses). If I’m working out the dope, I’ll just use a bigger target (paper or steel). At matches, a lot of targets don’t have a dirt background, so you often couldn’t see a miss. The projectile disappears into the foliage or falls somewhere down range. And we are not shooting a mile. Hopefully, you won’t have many misses to worry about, otherwise you are likely out of contention.
 
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