After a couple of years of loading 'proper' rifle cartridges, my father gave me his .357 carbine because he wasn't using it anymore.
I was used to crimping loads for .308, .270 and .303 with a Lee die, and my initial loads for the .357 I crimped to what felt like the same extent - i.e. pretty lightly.
After many scores of rounds which gave 3-4foot 'groups' at 100yds, I swallowed my pride and took some advice from someone who knew - which was to go for a markedly firmer crimp. I was initlally rather alarmed by the almost white-knuckle effort (relative to the use of the Lee die on the proper centrefires) that was required to sqeeze the case-mouth into the lead of the bullet (not into a 'crimping groove'), but the results were immediate and clear: actual groups!
Whether any of this is relevant to your situation, I don't know.
We have always known there were two Britains: one extraordinarily pleasant, inhabited by mild, tolerant, kindly people; the other utterly disgusting, inhabited by brutal and malevolent louts. Auberon Waugh