Author: britrifles
Subject: Effect of Primer Selection on Muzzle Velocity
Posted: January 31 2025 at 12:43pm
Heading back to the range tomorrow. Will shoot the T again and see if I can determine if the scope and mount affects muzzle “jump” and “compensation”. I will do this by shooting at 200 yards, with and without the scope fitted and shoot two different loads, 40.0 gr and 41.5 gr of Varget.
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Subject: Effect of Primer Selection on Muzzle Velocity
Posted: January 31 2025 at 12:43pm
Heading back to the range tomorrow. Will shoot the T again and see if I can determine if the scope and mount affects muzzle “jump” and “compensation”. I will do this by shooting at 200 yards, with and without the scope fitted and shoot two different loads, 40.0 gr and 41.5 gr of Varget.
The angle of “Jump” is the bullet angle of departure from the barrel relative to the direction the barrel is pointed before the shot is fired. Barrel vibration and action body flexure is what causes “jump”. While I can’t precisely measure that angle, I can determine the difference in angle of jump by shooting two different loads of different velocities with the scope and without. I can also see if the rifle shows any positive compensation with or without scope.
If there is compensation, fast bullets will hit the 200 yd target at a lower POI compare to slow bullets.
This figure illustrates how compensation works, an article written by Maj EGB Reynolds in the American Rifleman in 1969:
The difference in elevation POI between the two loads and with/without the scope will be different if the scope does indeed affect jump.
In reviewing last weeks tests on bullet seating depth, I realized that the last 10 shots of the 30 round test were quite good, even though they were five different bullet seating depths (OAL from 3.05 to 3.07 inches in .005 inch increments). Those ten shots had an elevation spread of just 1.35 MOA at 600 yds, well under the height of the MR target 10 ring. Perhaps this barrel does need some fouling to group well.