Jack Roberts
Moderator - Deceased
The following copyrighted material is reproduced here with the permission of Sierra Bullets. It is from Sierra's X-ring newsletter.
Jack
Volume 8 Number 2
Technical Newsletter From
Your Ballistic Technicians
Volume 8, No. 2
Putting A Chronograph To Work
by Paul Box
With the availability of more affordable chronographs coming on the shooting scene over the past twenty years, many shooters are adding this valuable tool to their equipment list. Most of us use one to tell us the velocity of our loads, but we're going to look at another aspect of load development using a chronograph. Our shooter (Bob), just bought a new 25-06 and wants to work up some varmint loads with the 87 gr. bullet. Bob starts working with IMR-4350 and loads three shells at the starting load and fires them checking both for accuracy and velocity. Pressures look fine so he bumps his load up a grain and checks again. Bob notices that each grain of increase is giving an average of 80 fps. Bob continues increasing his load and notices the primers are starting to flatten, but no other pressure signs are showing. Now the velocity increase has dropped to 30 fps. Bob becomes a little more cautious and increases the load by .5 of a grain and checks again. To his surprise the load drops in velocity by 15 fps. Even though no other pressure signs have occurred, the top has been reached. Every cartridge will have an efficiency range with a given combination of components. Once that range is passed, pressures will increase sharply and velocity will increase minimally. Changing to a different burning rate of powder will change this pressure curve and might give better velocity along with better accuracy. Bob now has the tool to find out.
Jack
Volume 8 Number 2
Technical Newsletter From
Your Ballistic Technicians
Volume 8, No. 2
Putting A Chronograph To Work
by Paul Box
With the availability of more affordable chronographs coming on the shooting scene over the past twenty years, many shooters are adding this valuable tool to their equipment list. Most of us use one to tell us the velocity of our loads, but we're going to look at another aspect of load development using a chronograph. Our shooter (Bob), just bought a new 25-06 and wants to work up some varmint loads with the 87 gr. bullet. Bob starts working with IMR-4350 and loads three shells at the starting load and fires them checking both for accuracy and velocity. Pressures look fine so he bumps his load up a grain and checks again. Bob notices that each grain of increase is giving an average of 80 fps. Bob continues increasing his load and notices the primers are starting to flatten, but no other pressure signs are showing. Now the velocity increase has dropped to 30 fps. Bob becomes a little more cautious and increases the load by .5 of a grain and checks again. To his surprise the load drops in velocity by 15 fps. Even though no other pressure signs have occurred, the top has been reached. Every cartridge will have an efficiency range with a given combination of components. Once that range is passed, pressures will increase sharply and velocity will increase minimally. Changing to a different burning rate of powder will change this pressure curve and might give better velocity along with better accuracy. Bob now has the tool to find out.
