I'm sure that primers make a difference when inappropiate primers are used such when regular primers are used when mag primers are needed to ignite heavily coated slow burning powder.
My question is do different brand primers affect group size when used with fast or medium burning rate powders and at the velocities of normal cast bullet velocities.
I have always been agnostic (promiscuous may be a better word) about primer selection using whatever was handy. It seemed to me that if they went bang they were all the same. I once tried the Federal 205M primers used by 99.9% of jb bench resters but couldn't see any improvement. I recently used some of these in a load and rifle that I have good records on. Nine 5-shot groups with 205M averaged substantially worse than usual with this load. I am skeptical but will try to repeat and see what happens.
Anecdotal evidence abounds about one primer or another causing either better or worse groups, but have there been any serious tests that have found repeatable differences in accuracy with different primer brands?