If you don't post the chambering, nobody will have a clue what to tell you.
Contact DRT. They'll likely have suggestions: (660) 564-2331. Since their bullets are frangible, they are likely longer than standard 55 grain bullets, will therefore stick deeper into the case and so will need to be used with a little less powder. Without the chambering and bullet length, though, I won't try to guess how much less.
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