Angle of departure

C

Charlie/Bravo

Inactive
Does angle of departure change depending on load? I've visited several ballistic web pages and cannot determine how this angle is arrived at....
Is it fixed and set by manufacturer of rifle or does this value change with bullet weight, powder charge, velocity or recoil etc.?
 
The bullet actually rises, in flight, from the muzzle, above the line of sight, then drops back down, crossing the line of sight or aim at some point, dropping below that line. Bullet mass, shape, and powder charge affects that flight path, along with barrel design.
 
Angle of Departure

I know that relative to line of sight the bullet rises.... then falls until reaching maximum point blank range then falls below line of sight.What I am asking is does the rifle scope location above the bore determine the angle of departure or does the rifle manufacturer have some sort of inclination built into the firearm? (e.g. +.04 degrees inclination) OR does riflescope or sights when adjusted determine angle of departure. P.S. Dave P. that utube video is a bit too deep for me.....
 
Oh boy ...

"The bullet actually rises, in flight, from the muzzle,..."

How does it do that? Do your bullets have wings? Mine don't.

Must we go into this ????
 
Sights were designed around actual test firing of differing caliber guns at a set distance, with stock ammo under varying conditions, years ago, by manufacturers and the military, where all that was recorded, and they do the same with new cartridges now. The gun manufacturer selects a sight for a specific cartridge size from a chart using barrel length, twist, etc, (and they might have to select another if that selection was incorrect), but when you are wildcatting new cartridges, you really don't know what you'll get until you try it, even though software and formulas have been developed, based on testing, to get one close. There's many variables in that, such as muzzle jump, the environment, the shooter, eye position, and other things, that make a fixed known angle, of the bullet of a selected cartridge leaving the barrel, impossible to know.

A sight or scope merely directs the eye along a straight line, and the elevation is based on targets at fixed distances, and how the selected cartridge performs at that distance. Rifles and pistols are different, in that a pistol has a short sighting radius, and a lot of muzzle jump, when compared to a rifle, thus the sights design is different. However, they were selected around actual test firing of that design. You may have a sight set where you are dead on, but a buddy may shoot that same rifle and cartridge, and have to reset the sight to match them. If you change to a different cartridge, then it will all change again.
 
The critics like to jump on this one.Some try to do less typing.They do not go through all the exercises to create the perfect PC statement .

Most of us could understand this thread without the following,but for the nit-pickers,and those who might just mis-understand,its really simple.

The theoretical "angle of departure" of the bullet from the axis of the bore is zero.Its straight.Now,imperfection of the bore or crown may introduce error,and recoil and or barrel harmonics may influence where the axis of the bore is pointed,but the angle of departure is theoretical zero.

But,there is another line.That would be line of sight.
Assuming the sights are above the barrel,if there were zero angle,the line of sight and the line of bore would be parallel.By definition,parallel lines never intersect.So there is no range where the POI would be the POA.

Gravity begins to act on the bullet the instant it leaves the bore.The bullet begins to drop immediately from the extension of the axis of the bore.

If the axis of the bore is where your mind is,there is no rise,only drop.

Its reall simple,not much to think about.

However,for those who are trying to discuss the usefulness of the rifle,and hitting things at range,the discussion is far more about the relationship of the sights to the flight of the bullet.

Assuming the rifle is sighted to hit POI/POA at a longer range,some portion of the bullets flight will be above the line of sight.

If a shooter wants to talk about "Rise" I will understand what he is trying to discuss and not muddy the water trying to impress with how brilliant I am.

To the OP,make yourself a drawing.Most trajectory data will provide you with "MOA" which really is Minute of Angle,or 1/60th degree.You can lookat all that in charts or software.But for your angle,the up close initial sight in range is the long leg of a triangle.Sight height above bore is the short leg.
Use a common unit of measure,divide the range into the sight height and it will give you the tan of the angle.Hit INV TAN function on your calculator and it will give you the angle.It will be decimal.If it is 1,or greater,write that down,then subtract the 1. there will be a 0.xxx decimal value for the fraction of angle.Multiply by 60 and it will give you the MOA value.



So,in common language,if you are sighted at 200 yds,the bullet must first "rise" the distance of the sight height.They might cross at ,say 30 yds.Your up close,initial sight in distance.Very little gravity drop has occurred.Line of sight intersects line of bore You have a triangle.While it won't be perfect,that is pretty much the angle you re looking for,I think,. That will give you enough info,rise over run,to calculate an angle.
Range to the short range target,and sight height above bore.

Then the bullet will "rise" to the peak of the midrange trajectory.That might be at about 150 yds.Then it will fall to point of impact on the target.
 
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I guess I could add, that the gun has nothing built in, per se, except that its design tries to align the shooters eye with the sight height, (which when the elevation is set at its lowest, its pretty much parallel to the bore), by the height of the comb of the stock. The compensation is all done by the sight elevation, and as HiBC says, when the elevation is adjusted for a far shot, and you look through a scope or at the sights, you are looking at a straight line to the target, but the farther out the target, the higher the elevation is set, and that causes the muzzle of the gun, or the center line of the bore to raise at the muzzle, creating an angle up. Thus, when the bullet leaves, it is actually aimed up, where the bores center line is pointed. That would be the angle that is different from a level line. When fired, eventually, the bullet passes through the line of sight, and some higher, in an arc, before it starts to drop, and where it intersects with the line of sight, again, is on the targets center.

As HiBC explains, there can be variables in all this, so no program or chart will be spot on, but it will get you close. That is why I say that a fixed or known angle is impossible to know.
 
Charlie Bravo,maybe I figured out what you are asking.

The bullet manufacturers have done enough testing and calculating on their bullets that they can give us what is called a Ballistic Coefficient.It is a number that is useful to calculate the drag of a bullet.More important to us,it tells us how the bullet loses velocity.

With a chronograph,we know velocity.

With a velocity and a Ballistic Co-efficient,other factors,altitude,barometric pressure,temp,humidity,all have an effect.With good inputs,a remarkably accurate bullet path can be predicted.

If we sight in our rifle at a known range,and enter the sight height,we can interface our sight info with the bullet path info.
As with all these calculations,garbage in,garbage out.

Used with care,the whole thing can be remarkably accurate.
 
The angle of departure is the angle between the line of the bore and the horizontal. That's all. The line of sight is something else.

Jim
 
Some good points made, a little terminology at:
www.deerhuntersclub.com/....shooting/bullet flight-and-hunting optics

May pop up just googling "Bullet Flight and Hunting Optics"

Also another interesting related topic is how shooting say a squirrel in a high tree or downward at something in a deep ravine finds vector force of gravity affecting POI quite differently from where you thought bullet would hit.
 
Angle of Departure

Thank you gentlemen for that easy to grasp explanation of relationship between the sights of rifle and actual bore sight. Most online animations and explanations concern themselves with bullet rise.... which of course causes one to believe there is some sort of inherent angle of bore with respect to line of sight. It's been over 45 years since I last fired a rifle... that is up until about 3 months ago. Back then the M.O. was full rock and roll "spray and pray". A lot has changed since then....
 
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Many years ago we went to the firing range with our M1 Garands; it had to be 1955. The range was a 1,000 inch range and I ask how does that work? And they said: "The bullet is the same height at 1,000 inches as it is at 100 yards".

That would be 27.77778 yards.

F. Guffey
 
Same height at 1000 inches as at 100 yards? Huh??

What they should have said is that if an M1 rifle is sighted so the bullet crosses the line of sight at 1000 inches (27 yards) on its way up to its maximum height it will then cross the line of sight again at 100 yards on its way down. And vice versa.

But that is too complicated for a bunch of "cruits" to grasp.

Jim
 
In normal rifle firing, the bullet crosses the line of sight twice, once on its way up, once on its way back down. For the most part, the first can be ignored and we concentrate on sighting the rifle so the bullet crosses the line of sight at the second point, the point at which the rifle is said to be "sighted in." But if a long range is not available, the rifle can be sighted at the point at which the bullet crosses the line of sight the first time, usually at 25-30 yards or so. Since the angle is less precise, shooting at the shorter range will not be as good as at the longer range, but it will allow firing of live ammunition with an scaled down view of the target,

Jim
 
And then one of us ask the sergeant to explain in ten words or less how the bullet and case hit the ground at the same time if the case is dropped when the bullet leaves the barrel. And then we wanted to know if the speed of the bullet and distance traveled changed anything.

F. Guffey

The one I was most proud of was the one that informed the General he had a good job if he did not mess up.
 
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