As Andrew said it’s mostly about bullet profile.
I always keep this picture handy so you can see the difference in pressure with deep seating.
If you have a 124 jacketed and 124 cast lead that now has a lube groove added in it ends up being a lot longer. Enough to make a difference depending on the load.
Also some of the slow powders like H110 get a little weird when they’re not loaded just right.
If you’re running a light cast bullet that has way less friction that jacketed and you’re running on the low end of the data then maybe that reduced friction and weight as just enough to effectively be one of those H110 light loads that gets kind of hairy.
That’s more of the exception not the rule. Most times people aren’t trying to push H110 max loads with cast bullets.
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