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

#15
12-13-2010, 07:13 AM
 Gold Member Join Date: Jun 2009 Location: Perry, Utah...now git off my lawn. Posts: 501
Re: **HELP** Need to understand trajectory(heavy VS light) in bullets.

Quote:
 Originally Posted by freebird63 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.
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Long Range Sickle
#16
12-13-2010, 07:21 AM
 Platinum Member Join Date: Jun 2001 Location: Potomac River Posts: 5,048
Re: **HELP** Need to understand trajectory(heavy VS light) in bullets.

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.
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The Smokin Fur Rifle Club
#17
12-13-2010, 07:57 AM
 Gold Member Join Date: Jun 2009 Location: Perry, Utah...now git off my lawn. Posts: 501
Re: **HELP** Need to understand trajectory(heavy VS light) in bullets.

Quote:
 Originally Posted by 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.
This is true. At 1000 yards, .5 moa is 5". Definately something to consider while doping your shots.
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Long Range Sickle
#18
12-13-2010, 08:43 AM
 Silver Member Join Date: Oct 2007 Posts: 156
Re: **HELP** Need to understand trajectory(heavy VS light) in bullets.

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
#19
12-13-2010, 09:17 AM
 Silver Member Join Date: Dec 2009 Location: Boise, Idaho Posts: 465
Re: **HELP** Need to understand trajectory(heavy VS light) in bullets.

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??
#20
12-13-2010, 09:29 AM
 Platinum Member Join Date: Apr 2010 Location: Allen, TX Posts: 2,608
Re: **HELP** Need to understand trajectory(heavy VS light) in bullets.

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.
#21
12-13-2010, 09:31 AM
 Platinum Member Join Date: Apr 2010 Location: Allen, TX Posts: 2,608
Re: **HELP** Need to understand trajectory(heavy VS light) in bullets.

Quote:
 "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

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