But that all changed in the 1980's after the ammo company folks changed the primer mixture for safety after a blast in Eley's Great Britian plant killed a couple employees. The best rimfire ammo made since has never equalled what the stuff before had for accuracy. No wonder that most of the smallbore records set before then still stand.
I have heard a number of people say that, Carl at Champions Shooters said it was the transition was from ether based primers to water based.
He said that while I looked at this 1971 ish factory target
I was discussing this after a small bore match and I told the group I would not pay a premium for 70’s/80’s ammunition as gunpowder does not get better as it ages. I was able to chronograph an old box of Eley, it was in a cardboard box, and the extreme velocity spreads were higher than the new stuff.