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Here is an article on Large Rifle Primers compared by Laurie Holland.

Ultimate Large Rifle Primer Shoot-Out — 16 Types Tested « Daily Bulletin

Interestingly, one of the magnum primers in the...

Here's an article on primers from the NRA. It mentions the undesirable aspect of using primers more powerful than needed.
https://www.nrafamily.org/articles/2020/4/26/3-things-to-know-about-primers

Man, just had a look around and a lot of sellers have run out of std primers but have the magnum but in some cases only in low quantities.

Would expect that some of the smaller guys may have some...

Mate did some testing in his darkened garage. Cannot recall which primers tested but using the eyeometer there were noticeable differences.

charliehorse Yep that's the one or very similar to the one I recall.
There's some extreme differences there isn't there?

In my 6.5AI using WW760 powder I succumbed to the "experts" and tried magnum primers.
Saw a fractional increase in velocity, opening up of ES, opening up of groups.
Reverted to BR2 primers. Maybe...