Seating stem for Berry's Flat point

[Thefeeder]

Which seating stem is used to seat Berry's plated plat point bulletshttps://www.berrysmfg.com/item/bp-38-357-125gr-fp

I will be using Dillon dies on a 550

[6mmintl]

I would try a wide stem made for round nose bullets, you might have to put in a hand drill and open up hole ( small knife blade, triangle scraper, file) and polish outer edges to not mark (ring) ogive.