Progression of ELR Community

[Deleted member 46119]

The aerodynamic considerations of a projectile

Coefficient of Drag
Center of balance (gravity)
Center of pressure
Gyroscopic Stability
Sectional Density

Hopefully I am putting all this together correctly. It's ok to correct me but please, this is not an opening for a slug fest. It's a mix of aerodynamics from high speed RC planes and ballistics. I'm trying to put this into simple terms.

Coefficient of drag is all about how the bullet has to push the air out of the way. There are interesting things that happen at the super sonic speeds our projectiles travel at and it changes as the velocity degrades.

Center of balance or center of gravity. Imagine balancing your bullet on the edge of a razor blade. This is one of the few things that does not change as the bullet flys. It does effect gyroscopic stability.

Center of pressure, this is where the air is pushing on the bullet as it flys. This moves around as the bullet speed changes. If the center of balance is fighting with the center of pressure it can effect accuracy.

Gyroscopic stability. This is where twist rate comes in. There is more to it than than twist. With out enough twist you bullet is like a "top" not spinning fast enough. It will wobble. If the center of balance, the center of pressure and the gyroscopic stability are all out of balance this is where you get 10" groups at 100 yards (ha ha). Seriously If these are all on song you are golden. Think about the twist, bullet shape and where the pressure is for the short range bench rest shooters. The bullet is shaped like a "top" as are most hand gun bullets. "Mythbusters" show where a 9mm is shot onto lake ice and it spins like a top for a long time. As far as I can tell with these flat based bullets the center of pressure is actually behind the bullet so does not influence the bullet.

All those things have compromises we make for the intended purpose of the projectile.

Leaving Sectional Density.

An object in motion tends to say in motion. Of course the follow on is "until influenced by some other factor". If bullets traveled in a vacuum they would never slow down. We all know this. Friction from air is our enemy but it will always be there. A method of countering aerodynamic drag is to keep the CD the same but increase the "mass" of the projectile. The more "mass" of the projectile the more atoms of what ever is in the air the projectile has to hit to slow it down. We call this sectional density.

Imagine swimming in ping pong balls. You are heavy, they are light. There is a lot more of them and every one you hit is slowing you down. Then think about diving into the ping pong balls. Now think about the perfect shape for getting through the ping pong balls. Except they ping pong balls rub against your sides slowing you down anyway, just not as much so you now have better aerodynamics.

One more factor we can add to get through the ping pong balls (air) is weight. If the weight (mass) is increased but everything else is the same you can get farther through the ping pong balls or in the case of a projectile air.

If you are still with me, I'm sorry to hear that. This is a bunch of drivel by a coffee starved idiot.

Because I have to do do something else right now I will summarize (simplified). CD+SD gives BC. CG+GS gives stability.

 

[THEIS]

Hello,

SOOO glad I never got into RC planes, much less high speed ones..that is a hobby I admire from a distance.

I follow what your saying..it is pretty much the methodology of lets say a 400gr .375 projectile being able to be "sized" to the footprint of a 325gr .375 projectile just by using tungsten "core" or any other heavy density alloy.
You get ALL the benefits of the 400gr mass with the drag footprint of the 325gr projectile.
You get ALL the center of gravity benefits from a shorter projectile. Easier to balance a 2" wooden pencil on its' eraser than a 6" wooden pencil on its' eraser.
Sorta like how baseballs are thrown faster than footballs..less surface area for air drag on baseball even though football should "slice" through air better (Of course there are other factors behind that, but for example sake..it explains it)

IMO projectile advancement is where the ELR community is lacking. And YES I realize there are some great shooting projectiles being made right now. Better than there ever has been, but that does not mean projectile design is not a lagging component in the sum of all things ELR.

****, Gale, Rock and some other guys were messing with 1000gr, 1050gr and 1100gr BMG projectiles made from stainless steel way way back. They knew then that heavier weight mass with smallest surface drag area was what was needed. Unfortunately they did not have the perks that we have today such as melonited barrels, projectile coatings such as HBN, etc etc so that projectile ate their barrels for lunch.
But it seems today projectiles are just getting longer and longer to keep up with weight mass race....

THEIS

 

[THEIS]

Hello,

Here is pic of 1990s technology design of using tungsten core to up weight and reduce drag footprint. Far right projectile has tungsten core inserted from tip of projectile.

THEIS

 

[Deleted member 46119]

Hello,

Here is pic of 1990s technology design of using tungsten core to up weight and reduce drag footprint. Far right projectile has tungsten core inserted from tip of projectile.

THEIS

Those look to be 50 cal bore riders.

 

[Deleted member 46119]

Hello,

SOOO glad I never got into RC planes, much less high speed ones..that is a hobby I admire from a distance.

I follow what your saying..it is pretty much the methodology of lets say a 400gr .375 projectile being able to be "sized" to the footprint of a 325gr .375 projectile just by using tungsten "core" or any other heavy density alloy.
You get ALL the benefits of the 400gr mass with the drag footprint of the 325gr projectile.
You get ALL the center of gravity benefits from a shorter projectile. Easier to balance a 2" wooden pencil on its' eraser than a 6" wooden pencil on its' eraser.
Sorta like how baseballs are thrown faster than footballs..less surface area for air drag on baseball even though football should "slice" through air better (Of course there are other factors behind that, but for example sake..it explains it)

IMO projectile advancement is where the ELR community is lacking. And YES I realize there are some great shooting projectiles being made right now. Better than there ever has been, but that does not mean projectile design is not a lagging component in the sum of all things ELR.

****, Gale, Rock and some other guys were messing with 1000gr, 1050gr and 1100gr BMG projectiles made from stainless steel way way back. They knew then that heavier weight mass with smallest surface drag area was what was needed. Unfortunately they did not have the perks that we have today such as melonited barrels, projectile coatings such as HBN, etc etc so that projectile ate their barrels for lunch.
But it seems today projectiles are just getting longer and longer to keep up with weight mass race....

THEIS

Ok, you got what I'm sayin.

Hey very fast powerful RC was a kick. 4500+ watts accelerating straight up to 150mph in less than 2 seconds. Whahoo.

 

[THEIS]

Those look to be 50 cal bore riders.

Those were the actual different projectile types and designs that MEN and HK come up with for the 9x cartridges.
Notice the slightly shorter length of the far right projectile than the others, even though the far right is 21gr heavier

THEIS

 

[Deleted member 46119]

Ok so know we know that upping the sectional density and keeping or reducing the coefficient of drag will raise the BC.

So the challenge is creating that projectile. As THEIS said, there is work with tungsten cored polymer bullets. I have not seen them but had rumor level information.

Because of my location I am very interested in non-toxic projectiles. I have looked at several metals and if they could be alloyed or sintered and the cost.

Tungsten would be a wonderful metal for this except......

Yeah there's always a catch on the cool stuff.

• Tungsten in purer forms is very hard on machining. However for us civilians that's not the issue.
• Tungsten cored projectiles are considered armor piercing AFAIK. That does not seem like a good long range bullet anyway.
• There are some discussions of tungsten toxicity.

We need something really heavy, not hard, not expensive and we are trying to get to non-toxic. For hunting, target and even the military are trying to switch to non-toxic.

Depleted uranium fits the weight thing but we get stuck on that armor piercing thing and of course it's not cheap. A GAU-8 round is supposed to cost $65 I don't know if that is a depleted uranium round but in any case DU is not available and would probably get you into trouble of you got some.

Gold, perfect very heavy. Not armor piercing. Great malleability for expansion. Oops wait, cost is a bit high. A 750 grain 50 cal is about 1.7 OZ so that comes in at $1,200 per OZ that makes a 50 cal round about $2,100. Well I guess we missed the mark again.

Gosh of we could just find some way to combine the good parts of tungsten, stay non-toxic and cheap.

Alloys and matrix combinations seem to hold promise but tungsten is still expensive.

So... What can we do?

 

[Deleted member 46119]

Bismuth bronze

From Wikipedia, the free encyclopedia

Bismuth bronze or "Bismuth brass" is a copper alloy which typically contains 1-3% bismuth by weight, although some alloys contain over 6% Bi. This bronze alloy is very corrosion-resistant, a property which makes it suitable for use in environments such as the ocean. Bismuth bronzes and brasses are more malleable, thermally conductive, and polish better than regular brasses. The most common industrial application of these metals are as bearings, however the material has been in use since the late nineteenth century as kitchenware and mirrors. Bismuth bronze was also found in ceremonial Inca knives at Machu Picchu.[1] Recently, pressure for the substitution of hazardous metals has increased and with it bismuth bronze is being marketed as a green alternative to leaded bronze bearings and bushings.

This material looks very interesting. Upping the percentage of bismouth to increase density. Bismouth by itself is 86% density of lead. Not bad.

Bismouth is not that expensive.

 

[THEIS]

Hello,

I am nowhere near knowledgeable on alloys and such but what is your thoughts on Molybdenum Copper or another alloy in combination with molybdenum. *Because of its lower density and more stable price, molybdenum is sometimes used in place of tungsten.

*wikipedia

THEIS

 

[Deleted member 46119]

Copper–tungsten

From Wikipedia, the free encyclopedia

Copper–tungsten (tungsten–copper, CuW, or WCu) is a mixture of copper and tungsten. As copper and tungsten are not mutually soluble, the material is composed of distinct particles of one metal dispersed in a matrix of the other one. The microstructure is therefore rather a metal matrix composite instead of a true alloy.

The material combines the properties of both metals, resulting in a material that is heat-resistant, ablation-resistant, highly thermally and electrically conductive, and easy to machine.

Parts are made from the CuW composite by pressing the tungsten particles into the desired shape, sintering the compacted part, then infiltrating with molten copper. Sheets, rods, and bars of the composite mixture are available as well.

Commonly used copper tungsten mixtures contains 10–50 wt.% of copper, the remaining portion being mostly tungsten. The typical properties is dependent on its composition. The mixture with less wt.% of copper has higher density, higher hardness, and higher resistivity. The typical density of CuW90, with 10% of copper, is 16.75 g/cm3 and 11.85 g/cm3 for CuW50 . CuW90 has higher hardness and resistivity of 260 HB kgf/mm2 and 6.5 µΩ.cm than CuW50.

Is this the holly grail we are looking for.

It's what I described earlier a heavy non-toxic sintered and infused to form a matrix.

Common materials, deformable, net density increase from lead.

The only drawback is developing the manufacturing process to reduce expense.

This process is even at a level where an experimenter/inventor level entrepreneur could have a go at making projectiles.

Density of lead is 11.34 g/cm3
Density of %50 copper %50 tungsten is 11.85

This has promise. There are even tungsten powder kits you can buy.

With the sintering process the shape of a core does not have to be the same as a lead core. things that improve gyroscopic stability.

Fun stuff. Now if I just had unlimited money.

 

[THEIS]

Density of lead is 11.34 g/cm3
Density of %50 copper %50 tungsten is 11.85

Mi-Techmetals has 55%T/45%C listed at 12.50g/cc and 68%T/38%C listed at 13.93g/cc

With readily available rods

THEIS

 

[THEIS]

Hello,

Replace the soft aluminum zinc alloy core of this projectile with something like tungsten copper. Seat it in a brass "shoe" and polymer coat...the brass "shoe" area is the only part of the projectile that engages the barrel rifling.

Now just need a new cartridge case design

THEIS

 

[Deleted member 46119]

Mi-Techmetals has 55%T/45%C listed at 12.50g/cc and 68%T/38%C listed at 13.93g/cc

With readily available rods

THEIS

Tungsten gets heavy fast. It also gets hard fast. Gotta watch the "armor piercing" threshold.

 

[Deleted member 46119]

Hello,

Replace the soft aluminum zinc alloy core of this projectile with something like tungsten copper. Seat it in a brass "shoe" and polymer coat...the brass "shoe" area is the only part of the projectile that engages the barrel rifling.

Now just need a new cartridge case design

THEIS

The static and dynamic aspects of that projectile suck.

The construction is close to where I want to go with this idea.

I'm also not keen on machining W55Cu45. I wonder if you got @RockyMtnMT some, if he would give it a go.