**HELP** Need to understand trajectory(heavy VS light) in bullets.

[LRSickle]

My point was or is, if the riflings are clockwise or counter clockwise, if the riflings are clockwise and the closkwise spin causes the bullet to fall to the earth faster then say a barrel with riflings that were counter clockwise??? have there ever been any experiments with that???? because in my little simple twisted mind it almost makes sense that if a barrel that had clockwise riflings and with the clockwise spin of the bullet it would cause the bullet to fall back to the earth faster then a barrel with a counter clockwise riflings causing the bullet to spin counter clockwise?? also we would have to factor in the rotation of the earth. Welcome to my world, these are just questions I have.
Chuck

A righthanded twist causes the bullet to hit high/left in a right-to-left wind and low/right in a left-to-right wind. It would be exactly the opposite in a left-handed barrel. So whether you have a right or left twist doesn't matter, you still have the same advantage/disadvantage.

The earth's rotation does effect the bullet's flight. It's called the Corialis effect. If your shooting from north to south and the earth's surface is turning to the east at 750mph, your bullet will hit right. For that brief time that your bullet is in flight, in limbo so to speak, the target has moved to the left at 750mph causing your bullet to hit right. This is something that I could never be able to detect so I don't worry about it. Pretty interesting though.
Chuck J.

 

[Buffalobob]

Spin drift and corealis effect are small terms. Even so several of the new versions of ballistics programs will compute them. Typically at 1000 yards with the bullets I use, spin drift is about a half MOA.

As far as falling to earth one should remember that the whole point of knowing your ballistics is to tilt the barrel up so you fall to earth at the location of the animal. This process can be up to several seconds for shoots out in the 1500 yard range.

 

[LRSickle]

Spin drift and corealis effect are small terms. Even so several of the new versions of ballistics programs will compute them. Typically at 1000 yards with the bullets I use, spin drift is about a half MOA.

As far as falling to earth one should remember that the whole point of knowing your ballistics is to tilt the barrel up so you fall to earth at the location of the animal. This process can be up to several seconds for shoots out in the 1500 yard range.

This is true. At 1000 yards, .5 moa is 5". Definately something to consider while doping your shots.

 

[aroshtr]

Trajectory (original question):
It has been my experiance that up to about 500-600 yards, with typical hunting calibers, it is more benificial to use the light fast bullet. This is for both trajectory and wind (time of flight). Beyond 600 the numbers always seem to favor the heavier bullets. I feel this is mostly for wind, but trajectory benifits start to come into play beyond 800 yards.

Spin Drift:
I agree that bullets will climb (actually fall less) and fall faster than expected depending on which way the wind is blowing. But in a no wind situation, keep in mind that you will always have spin drift to the right with a right twist barrel. This is directly tied the RPM (twist rate of your barrel and velocity), the length/BC of the bullet, and air density. The reason you will always have spin drift to the right in a right twist barrel is that your bullet is falling at about 22mph (newtons 9.8mps2 is roughly 22mph for the first second). Thus it would take a severe wind for the elevation change due to crosswind to even equal the drift from the falling bullet. Condisering the spin drift up to 1000yrds is usually .5-.75moa, I don't think a hunter should even consider the vertical component of spin drift due to wind. I know I won't be taking a 1000yrd shot at an animal in a 20mph wind.....

aroshtr

 

[freebird63]

Now as far as wind effect on the bullet goes, we all know that if you have a cross wind in your bullet path its going to cause your bullet to either go left or right. What effect does the wind have on your bullet if its a head wind or a tail wind?? I would think a tail wind would cause your bullet to be less stabilized during flight, especially with a boat tail design.
Another question I have always had is what would happen if your bullet, it being a boattail design, if the bullet had a concave design??, I believe that is the correct word I am looking for, it would almost kinda resemble a hollow point, but much bigger on the tail end of the bullet??

 

[rscott5028]

According to Sierra as cited by Buffalobob, a tail wind results in less drag and higher POI while a head wind increases drag resulting in lower POI.

exterior ballistics

A lot of these things are relatively small factors compared to breathing and trigger control.

I'm not aware of anyone making concave ogives. But, if someone comes up with a lightweight bullet with low BC that opens up into a Rage Broadhead at impact. I'll be first in line to give it a try. ;-)

Until then, I'm using heavy bullets for caliber with high BC and proven lethality for long range hunting.

 

[rscott5028]

"But, if someone comes up with a lightweight bullet with low BC that opens up into a Rage Broadhead at impact."

I meant high BC. duhhh

 

[rscott5028]

You also have to take the gun into account. As for the minutia, I suspect the rifling of different guns could have a tiny impact on the grooves that intereact with the wind.

But, more important is the rifle as a system and which bullets it likes to shoot. I've had ideal bullets in mind before and been unsuccessful working up a satisfactory load in a given rifle only to switch to another bullet with great success. That's not to say that I did all the right things to optimize the load.

But, you have to move from pure theory to practical when you go to the field.

So, back to the origin of this thread... Pick the bullet that you like. And test it in your rifle. Try them all if you have the time and budget.

 

[Buano]

... Another question I have always had is what would happen if your bullet, it being a boattail design, if the bullet had a concave design??, I believe that is the correct word I am looking for, it would almost kinda resemble a hollow point, but much bigger on the tail end of the bullet??

A concave tail on s bullet (an inside-out boat-tail) would cause an increase in turbulence, which translates to an increase in drag, which in turn means the bullet would lose speed & energy faster (as compared to traditional bullets) as it flew through the air.

 

[rscott5028]

In that case, you could fill the tail with plastic. But, why not just go to a lighter weight material altogether such as an all copper bullet.

Along those lines, the question I've had is why doesn't Barnes have a higher BC? Is it their overall shape? Or, is it that they would have to get extroardinarily long in order to match Berger's BC while reducing case capacity and creating pressure problems?

...besides the fact that impact velocity needs to be >1900fps for proper expansion.

 

[Buano]

In that case, you could fill the tail with plastic. But, why not just go to a lighter weight material altogether such as an all copper bullet.

Along those lines, the question I've had is why doesn't Barnes have a higher BC? Is it their overall shape? Or, is it that they would have to get extroardinarily long in order to match Berger's BC while reducing case capacity and creating pressure problems?

...besides the fact that impact velocity needs to be >1900fps for proper expansion.

Bullets have advantages if they are as dense as possible since a more dense bullet will have more inertia (to maintain speed & to transfer to the target) than an identically shaped lighter bullet. Adding a plastic section to the tail defeats that premise. Polycarbonate tips have appeared on the market since they maintain their shape better than pointed lead, which (customers believe) makes them more accurate.

 

[rscott5028]

Polycarbonate tips have appeared on the market since they maintain their shape better than pointed lead, which (customers believe) makes them more accurate.

Amen.

Customers beleive a lot of things that aren't necessarily true when put into practice. Manufacturers sometimes create the myths/gimmicks or go along with them because often times it really doesn't matter. Dead is dead. And, that's good enough for many folks. Plus there are many hunting/shooting situations.

I neck turn, weigh every charge, check concentricity, etc... Why? Because I live in the city now and only get to hunt a few days a year. I target practice a lot. ...and, arguably spend too much time studying theory and optimizing loads.

I have a brother who I can outshoot at 1k because I've studied and prepared. He has more trophies on the wall because he still lives on the ranch and carries his 270 and factory ammo everywhere he goes.

 

[Kevin Thomas]

The earth's rotation does effect the bullet's flight. It's called the Corialis effect. If your shooting from north to south and the earth's surface is turning to the east at 750mph, your bullet will hit right. For that brief time that your bullet is in flight, in limbo so to speak, the target has moved to the left at 750mph causing your bullet to hit right. This is something that I could never be able to detect so I don't worry about it. Pretty interesting though.
Chuck J.

An accurate description of the Coriolis effect, and an interesting thread here. For what it's worth, at one time, I believe it was Colt that rifled their guns in one way for sales in the Northern Hemisphere, and the opposite for sales in teh Southern Hemisphere. They eventually discontinued when it was determined that the difference caused by the Coriolis effect was, "measureable, but negligable." As you can envision by Chuck's description here, it's a matter of time of flight. For the second and a half to three seconds that our small arms bullets are in flight, the distance involved is minor. You also have to take into account that this effect changes with the azimuth in which the shot is taken, East/West (or vice versa) shots should show virtually no difference. Those taken along a North/South axis will show something. But again, it's repeatable, so after the sight's clicked a minute or so to correct, that's the end of it from that firing position and target.

Longer times of flight, such as that seen in artillery, the difference becomes very pronounced, and it MUST be taken into account and corrected for. Is it any wonder that the first real computers were designed to control naval gunnery? Stop and think about the physics here for a moment. Two battleships engage at a distance of 20 miles or so. The times of flight for their main gun projectiles are 30-45 seconds or more, you're dealing with vessels that have a top speed of 30 knots, making a combined closure speed of something near 70 MPH. Add the fact that each can be heading in any azimuth relative to the other. Now try to solve that ballistics problem in a hurry when the other guy is lobbing 15" shells at you. No pressure.

When we get into ICBMs coming over the pole with flight times of 30 minutes or so, again, it's a factor that HAS to be taken into account and corrected for. Example: The Russians aim their ICBM at Kansas City, and forget to calculate Coriolis into the equation. Thirty minutes later, they wind up hitting St. Louis instead. (Whether that's a good thing or not is probably a topic for another thread, depending on whether your a Chiefs or Rams fan). Either way, it was the Coriolis factor that caused the miss.

ICBMs, 15" shells fired from the Bismarck, or a 210 grain Berger from a 300 Win Mag, it's all the same thing, differeing only in matters of scale and degree.

 

[Bert]

after reading this entire post i'm less enlighten than ever i was thinking of changing to a 150 gr insted of 165 gr for longer shots for me that would be 500yds on deer . After reading this post i think i can leave things the way they are .I shoot 165gr nosler partition ,imr4831,58.2gr 30 06 sako