Primers and accuracy

Can changing only a primer affect group size?
YES! It can, and does...
The first picture. Excuse the 22 caliber holes on the top left of my target. I accidentally shot a group on my friend Dave’s plaster.
This is a five shot 100 yard group with CCI BR-2 primers. This group measures 3/4”

The second picture is also a 5 shot group at 100 yards with Federal 210 Gold Medal match primers.
This group measured 1/2”

The third group was fired with Federal 215 Gold Medal match primers
This group measured 1/4”

All the loads were identical with the exception of the primers....
 

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Has to be the consistency of the manufacturing
Not necessarily. It has a lot to do with the bristince, flame duration, and flame temperature.
All the primes used came from good and established lots.
This pertains to loading density and powder composition.
I was loading a ball powder with a high load density, and that’s most likely why the hotter Federal 215’s gave the smallest group. It ignited more powder quicker for a faster and more complet powder burn.
 
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