explain this

[smoakingun]

OK, I'm not new to this, but I don't understand what I am seeing. I recently decided to take the scope off of my 45-70 guide gun and go back to iron sights because it makes it a much more handy rifle. here is the wierd part, I noticed during sight in that with a 100yd zero, the rifle shoots high at 75 and 50 yards, but LOW at 25 yards. thinking that it was a fluke, I imediately repeated the process, 4 more times, 5 rounds at each range, 4 more times, with exactly the same result. any idea why?

 

[aeonrevolution]

Depending on the bullet...usually it raises a bit and then proceeds to drop.

Heres an example from my 762x54r. Different bullets would presumably raise until different distances.

 

[Scorch]

This is especially noticeable with cartridges that have very arced trajectories. Remember, trajectories are not flat (the bullet starts to drop at 32 ft/sec/sec as soon as it exits the rifle's muzzle), the bullet is launched at a slight upwards angle so its path crosses the line of sight, otherwise there would be no way to aim for a specific spot. At 25 yds you are below the line of sight, at 50 yds you have risen to the line of sight, at 75 yds you are above the line of sight, and at 100 yds the bullet is dropping back to the line of sight. With some very flat-shooting cartridges (think 22-250, 220 Swift, 204 Ruger), if you sight at 100 yds you may be below the line of sight all the way to about 90 yds.

 

[bedlamite]

Another graph that demonstrates trajectory:

 

[jammin1237]

smoakingun,
just take a look at the chart that aeon gave...

think of the linear grid lines as your point of aim, then try to figure out where the bullet will go...


just because you see it in your sights does not mean the bullet will get there

 

[paladin-34]

smokingun this is caused by the hight of the sights above the barrel. it should have been more pronounced with the scope. pick a point above the ballistic curves shown above and draw a streaght line through 100yd location of the bullet (call this the sight line. you will notice that the further a sights start from the barrel the more the impact point is below the sight line.

Joe

 

[jammin1237]

the main problem is that for some reason everyone thinks that a bullet will travel in a flat line, well it doesnt!... it starts to drop the very microsecond it leaves the barrel, unless the path is altered by ... hhhmmm lets say recoil or kick... in which the barrel rises and changes the hyperbolic curve of trajectory...

 

[j.chappell]

the main problem is that for some reason everyone thinks that a bullet will travel in a flat line, well it doesnt!... it starts to drop the very microsecond it leaves the barrel

The bullet will only drop the "microsecond" it leaves the barrel if the bore is level or is in a downward angle at the time the bullet exits the muzzle.

unless the path is altered by ... hhhmmm lets say recoil or kick... in which the barrel rises and changes the hyperbolic curve of trajectory

This happens every single time a firearm is fired. Not only do you have the actual muzzle jump but you also have the harmonics of the barrel that cause the bullet to exit the barrel at differing angles.

J.

 

[jmr40]

This is perfectly normal with all guns. It did the same with the scope on the gun, you just never noticed it. With any sights, scope or irons, the muzzle is going to be elevated slightly higher than the breech. Because the bore is below the sights and the muzzle is slightly elevated the bullet will start out lower than your line of sight. When the bullet leaves the muzzle it is in an upward arc and will cross your line of sight at some point. In your case somewhere between 25 and 50 yards.

Between 50 and 100 yards your bullet was above your line of sight and at some point it reached the apex and started to fall. If your gun is zeroed at 100 yards it again crossed your line of sight at that range.

This is ture with all cartridges but is much more noticeable with rounds like the 45-70. With flatter shooting rounds like the 30-06 or 270, if they are zeroed at 100 yards the distance they are either below, or above the line of sight is so slight that most shooters never notice it.

 

[smoakingun]

thanks for the info, I didn't realize that at 25yds the bullet had not yet crossed the line of sight. I kinda thunk it, but it doesn't seem right, I believe what you are showing me, it just didn't register untill I saw the graph