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Discussion in 'Reloading' started by dewiseman, Jul 4, 2009.
What purpose does a chronograph serve in developing handloads?
A chronograph lets you verify your load versus the expected velocities in the load manuals, this gives you some confidence that the pressure is in a safe range.
Secondarliy, the consistency (or lack thereof) of the velocity will give you an idea if the load may be useful for long range shooting. A low Standard deviation and low extreme velocity spread are good indications of a consistent load.
Thirdly, velocity is a key input into the ballistic calculators, which are used to give you an initial drop chart.
1. Known velocity in your rifle - The books are a good guide but that can be off quite a bit and velocity will vary from rifle to rifle. If shooting longrange than it is VERY important to know your muzzle velocity, among other things.
2. Standard deviation (SD) - generally speaking, a load which displays a low standard deviation (preferably single digits) is a good sign for a consistent and potentially accurate load. However, loads with low SD are not always the most accurate.
A low SD is important when shooting at long range. Obviously if two bullets leave the muzzle at different velocities they will impact much farther apart when shooting at extended distances. Hopefully your initial muzzle velocities are as close as possible to each other for consistent bullet drop.
I'm sure there are other uses for chronograph data but these two issues are what interest me.
More than anything it will save you time and money.
I use to go by group size and found that a good group at 100 yards did not guaranty
a good group at 600 yards because the SDs could be bad and at 100yrds still shoot
So now I load 3 test loads for each powder weight with the bullet I want to use and
fire 2 then check the SDs , and if they are over 15 I save the 3rd round and pull and
When I find a load in the single digits then I shoot the 3rd round to see if the SDs hold.
Now to improve accuracy I load that load with different bullet seating depths until I
get the best accuracy. and if it shoots 1/2 MOA at 100yards then it will shoot close
to that at 600 or 1000yrds if I do my part and have choosing a good bullet for long range.
There are many advantages in using a chronograph because they give you a history
to go back to if you have to change powder lots.
J E CUSTOM
Plus 1 on what has already been posted about needing to know the velocity for long range shooting to develop drop tables. One thing a chrono will do is make you shake your head when comparing data in reload manuals to what you are getting in your firearms. It will show that a lot of data in manuals (not all) are 100-200-300 feet per second slower than what the manual says they achieved with a certain load. You can get better info as to which primer brand gives the most consistent velocity. I've seen in some testing that when getting near maximum velocity the velocity increase with powder increments drops off. For instance if every .5 grains of powder increase gives approx. 75 fps more velocity and when getting near maximum the increase may drop down to 30 or so. I've seen this often but not in every case. I loaded for years without one and simply thought that my favorite load according to the book was going 2900fps and found out that actually it was only 2750. Just another gadget for loading and shooting but a useful one.