Greetings Thatguy,
I had a scratch through an old pile of Handloader magazines and turned up an article on the 454 in 1994. The Author made 2 recommendations. First not to reduce 296 loads below start loads. Second was to apply a very firm crimp to the hotter loads. He was using a Freedom Arms revolver so the crimp could have been to stop the projectiles moving forward and jamming the cylinder or it could have been to help the powder ignite properly or both. His loads were fire cracker hot for the freedom revolver and probably excessive in your much weaker Rossi so they will not be mentioned. So one thing that you could try, if you haven't already is a firm roll crimp. Zimmer mentioned this in his post although in his case it did not help. This will need a projectile with a crimp groove. Your seating or crimp die should be able to do this. I should point out that I have zero practical experience in loading pistol cartridges but am an insatiable reader of the Handloader articles.
Regards Grandpamac.
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