Long old guy ramble.
We get interested in other’s question..esp. the ones that seem simple, but turn out to be complex.
I just always liked pump .22’s. Winchesters, Remingtons, Rossi clones, Taurus clones, Savage, Noble, etc. Not a collector, were just working guns that passed though.
Some (that were able) were scoped, some tank sighted, most were open iron. While I didn’t consider them target guns, they did see some paper shooting.
Good clean oldies got valuable, for what I was doing, would be better to beat up a clone.
Most of the other action types would “kind of feed” the shorter rounds. Not too many “other action types” were made to function with all three lengths on .22RF’s. That was the draw to pumps...they cycled normally with nearly anything…..22 shorts and CB’s got used often.
They all seemed to show more shift than other rifle types. 4” of total spread is more than I’ve found unless I was running .22ammo that was extremely different (CB caps, non lead, 60gr.,sub-sonic, hyper sonic, etc). Basically trying to make it happen.
Horizontal shifts and vertical shifts….most gave a bit of both. Do not remember anything that spread as far at short range as the 4” you mention, other than ammo that was so inaccurate the “groups” were just kind of random holes.
Current ammo situation makes that kind of testing near impossible.
Gave up on the “why”...sometimes it just is what it is. So long as the groups were always in the same place and the same size when tested, it was a useful .22.
IF I found just a vertical difference between ammo (say .22 short Vs. .22LR)… open sights with a step elevator sometimes would make that a one step difference….other times, I’d have to file one of the steps to get that one-step effect.
I put it down to barrel vibrations and changes in stress in a “wiggly” system. Tube mags, a moving fore end that gets shucked back and forth...they do seem to respond to grip pressure. Some are better at isolating the forearm mechanics than others.