Hammer
10-18-2009, 01:20 PM
In the October 2009 The Varmint Hunter there is an article titled “Varmint Rifle Accuracy vs. Target Size and Distance.”
Using root mean square radius (RMSR) calculations to determine the shooting accuracy (gun, ammo, and shooter), the size of the target’s vital area, and distance to the target – the author Roy Welch develops a table for the maximum distance that 70% of the shots fired will hit the vital area of the target. He uses 70% because his targets are varmints and not big game animals and because approximately 70% numbers are easy to calculate.
The accuracy of the shooting system (gun, ammo, and shooter) has a lot more effect on shortening the distance for hitting the varmint target than I would have guessed.
RMSR in MOA 0.25 0.50 0.75 1.00 1.50
Group Size (five shot) * 0.58 1.17 1.75 2.33 3.50
Maximum Distance in Yards for Shot at Varmint
Varmint
Groundhog 665 335 220 165 110
Prairie dog 570 285 190 145 95
Ground squirrel 380 190 125 95 65
* My poor unthinking guestimate for converting RMSR to five-shot group size at 100 yards.
Sorry, cannot get the columns to line up properly, so you will have to count them.
In addition to the true skill involved, does add a better sense of the luck involved in reported prairie dog hits beyond 500 and 1,000 yards.
Also makes me not feel so bad when I tell the prairie dog guide that I have no interest in shots beyond 300 yards, though they want to emphasize lining up for 500+ yards.
Everyone has in their wallet a less than half-inch three-shot group that he has fired one time with his favorite rifle from a bench in no wind conditions.
The gun/ammo/shooter combination that will average five-shot groups day-in and day-out less than half-inch in windy field conditions may be less than some might wish to consider.
During the 2008 National Benchrest Rifle Championships there were 738 five-shot groups fired at 100 yards. This was all with the benefit of the best shooters in the world, best rifles and ammo in the world, and thousands of wind flags properly placed and used. Shooting was done from mechanical rests on concrete benches. Typical rifle barrel costs was $500 before chambering and installing. Maximum rifle weight was 10˝ pounds. Scopes were mostly Leupolds with 45X magnification. The average recorded group was 0.282 inches. Ninety-nine percent of the groups were less than 0.526 inches.
How does your varmint rifle average in the field ? What is its 99% limit for maximum group size ? At what distance can you average 70% vital hits on groundhogs or prairie dogs ?
Using root mean square radius (RMSR) calculations to determine the shooting accuracy (gun, ammo, and shooter), the size of the target’s vital area, and distance to the target – the author Roy Welch develops a table for the maximum distance that 70% of the shots fired will hit the vital area of the target. He uses 70% because his targets are varmints and not big game animals and because approximately 70% numbers are easy to calculate.
The accuracy of the shooting system (gun, ammo, and shooter) has a lot more effect on shortening the distance for hitting the varmint target than I would have guessed.
RMSR in MOA 0.25 0.50 0.75 1.00 1.50
Group Size (five shot) * 0.58 1.17 1.75 2.33 3.50
Maximum Distance in Yards for Shot at Varmint
Varmint
Groundhog 665 335 220 165 110
Prairie dog 570 285 190 145 95
Ground squirrel 380 190 125 95 65
* My poor unthinking guestimate for converting RMSR to five-shot group size at 100 yards.
Sorry, cannot get the columns to line up properly, so you will have to count them.
In addition to the true skill involved, does add a better sense of the luck involved in reported prairie dog hits beyond 500 and 1,000 yards.
Also makes me not feel so bad when I tell the prairie dog guide that I have no interest in shots beyond 300 yards, though they want to emphasize lining up for 500+ yards.
Everyone has in their wallet a less than half-inch three-shot group that he has fired one time with his favorite rifle from a bench in no wind conditions.
The gun/ammo/shooter combination that will average five-shot groups day-in and day-out less than half-inch in windy field conditions may be less than some might wish to consider.
During the 2008 National Benchrest Rifle Championships there were 738 five-shot groups fired at 100 yards. This was all with the benefit of the best shooters in the world, best rifles and ammo in the world, and thousands of wind flags properly placed and used. Shooting was done from mechanical rests on concrete benches. Typical rifle barrel costs was $500 before chambering and installing. Maximum rifle weight was 10˝ pounds. Scopes were mostly Leupolds with 45X magnification. The average recorded group was 0.282 inches. Ninety-nine percent of the groups were less than 0.526 inches.
How does your varmint rifle average in the field ? What is its 99% limit for maximum group size ? At what distance can you average 70% vital hits on groundhogs or prairie dogs ?