I would check for parallax at 400.
I have seen people shoot low with BDC reticle due to parallax error just as you describe.
Truing for BC - experience with accuracy of Barnes stated BC
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I would check for parallax at 400.
I have seen people shoot low with BDC reticle due to parallax error just as you describe.
med358-boise
Well-Known Member
4th point,
Can you explain more as I have never really understood how parallax works. I know parallax is different than focus and that scopes (unless they have a parallax adjustment) can only have parallax set at one distance.
In the PRS competition world, a common "truing of DOPE" technique is:
1) Chrono load in your rifle - input speed and bullet into one of multiple ballistic apps (Hornady 4DOP, Applied Ballistics, etc.)
2) "True" velocity to 600 - velocity is the key variable to 600 yards or so
3) "True" BC at 800 yards or as far as you can - BC is key variable at extended ranges
If you are shooting less than 500 yards - velocity is the key and BC not as much
1) Chrono load in your rifle - input speed and bullet into one of multiple ballistic apps (Hornady 4DOP, Applied Ballistics, etc.)
2) "True" velocity to 600 - velocity is the key variable to 600 yards or so
3) "True" BC at 800 yards or as far as you can - BC is key variable at extended ranges
If you are shooting less than 500 yards - velocity is the key and BC not as much
Set up your rifle so that you can view through the scope without moving the rifle. Move your head slightly, side to side, then up and down.
Do this while viewing something at 400 yards.
I bet that you will see the reticle move. Up and down, as you move your head slightly up and down. If so, that is likely the issue, especially from field positions.
med358-boise
Well-Known Member
4th point,
I may be exposing "my stupidity here" but I assume what happens then is that "I don't realize my head has moved slightly, so then I adjust the hold" and create the error?
I may be exposing "my stupidity here" but I assume what happens then is that "I don't realize my head has moved slightly, so then I adjust the hold" and create the error?
Doom2
Well-Known Member
The drop to 400 yds in most cartridge is not a strong function of BC. The usual recommendation is to true using velocity out to about 600yds and then use measured velocity and adjust the BC to match actual beyond that point. You have to remember that whether you are using G1 or G7 it's likely that neither model actually fits the bullet you are shooting so some deviations are likely to show up (Post #13 ).
yobuck
Well-Known Member
yobuck
Well-Known Member
Your analysis is correct, but you should read up on the subject of parralex.
In a nutshell, all scopes used for long range, or serious target shooting are best if they can be adjusted for parralex.
As for adjusting drop charts for the B C of a bullet at various distances, its sort of like the cat who chases its own tail.
Actually, its not even necessary to have a chronograph in order to confirm velocity for making an elevation chart.
We as a rule develop loads based on accuracy, and the velocity is whatever it is regardless of the B C of the bullet we used.
So if we zero the scope at say 100 yards with our new load, and then count the additional clicks required to hit a target at say 400 yards, we can compare that information with one of the data providers like say JBM to tell us what the velocity is.
Of coarse it helps to have a ball park idea of the velocity number to start with.
For example, if we guessed the velocity to be 2900 fps, the amount of clicks we added might show it to be more or less when compared with the data provider.
That is the true velocity, not what the chronagraph claims it to be.
Again, it is whatever it is, and tomorrow, when the air temp. is 20 deg. colder, it will be whatever it is all over again.
In a nutshell, all scopes used for long range, or serious target shooting are best if they can be adjusted for parralex.
As for adjusting drop charts for the B C of a bullet at various distances, its sort of like the cat who chases its own tail.
Actually, its not even necessary to have a chronograph in order to confirm velocity for making an elevation chart.
We as a rule develop loads based on accuracy, and the velocity is whatever it is regardless of the B C of the bullet we used.
So if we zero the scope at say 100 yards with our new load, and then count the additional clicks required to hit a target at say 400 yards, we can compare that information with one of the data providers like say JBM to tell us what the velocity is.
Of coarse it helps to have a ball park idea of the velocity number to start with.
For example, if we guessed the velocity to be 2900 fps, the amount of clicks we added might show it to be more or less when compared with the data provider.
That is the true velocity, not what the chronagraph claims it to be.
Again, it is whatever it is, and tomorrow, when the air temp. is 20 deg. colder, it will be whatever it is all over again.
JustMe2
Well-Known Member
Med 358, BC is an expression of bullet drag. Bullet drag is influenced by bullet shape, velocity, humidity, altitude, and temperature (density altitude).
The BC number is constantly changing from the muzzle to the target. BC is not the same number at 0 yds, 50 yds, 100 yds, etc. The single BC number is actually an average of the BCs measured over a certain distance.
Drag (BC) increases as humidity increases because the bullet is hitting more water particles.
Drag (BC) increases as the temperature decreases. The particles in the air are packed closer together the colder the air. Consequently the bullet strikes more air molecules in cold air.
Drag (BC) increases the lower the altitude. Air is denser in a valley than on a 5000 ft mountain. The bullet strikes more molecules in the valley increasing drag.
Drag (BC) increases as the velocity increases. The bullet compresses more air in front of it the faster it flies therefore striking more molecules. Sort of, since this phenomenon changes for supersonic and subsonic flight.
Drag increases the less aerodynamic the bullet design. A pointed bullet compresses less air in front of it and has less drag than a blunt bullet, so BC will change faster over distance with a blunt bullet.
Bullet center of gravity (CG wobble), etc., etc.
In conclusion, how different were your shooting conditions than the manufacturer's conditions in an indoor, no wind, airconditioned facility at what altitude, what velocity, etc?
Now factor in scope parallax error (lens alignment), scope reticle drop error (spacing between holdover lines, not the same on all scopes), dialing click error (accuracy of gear teeth inside the scope), etc.
Strelok app has reticles for thousands of scope reticles that may give you more accurate drops for your scope reticle.
It's magic how we can hit anything, LOL.
The BC number is constantly changing from the muzzle to the target. BC is not the same number at 0 yds, 50 yds, 100 yds, etc. The single BC number is actually an average of the BCs measured over a certain distance.
Drag (BC) increases as humidity increases because the bullet is hitting more water particles.
Drag (BC) increases as the temperature decreases. The particles in the air are packed closer together the colder the air. Consequently the bullet strikes more air molecules in cold air.
Drag (BC) increases the lower the altitude. Air is denser in a valley than on a 5000 ft mountain. The bullet strikes more molecules in the valley increasing drag.
Drag (BC) increases as the velocity increases. The bullet compresses more air in front of it the faster it flies therefore striking more molecules. Sort of, since this phenomenon changes for supersonic and subsonic flight.
Drag increases the less aerodynamic the bullet design. A pointed bullet compresses less air in front of it and has less drag than a blunt bullet, so BC will change faster over distance with a blunt bullet.
Bullet center of gravity (CG wobble), etc., etc.
In conclusion, how different were your shooting conditions than the manufacturer's conditions in an indoor, no wind, airconditioned facility at what altitude, what velocity, etc?
Now factor in scope parallax error (lens alignment), scope reticle drop error (spacing between holdover lines, not the same on all scopes), dialing click error (accuracy of gear teeth inside the scope), etc.
Strelok app has reticles for thousands of scope reticles that may give you more accurate drops for your scope reticle.
It's magic how we can hit anything, LOL.
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