I ran an oversized ~.35975 cast through my .357 mag and had to drive them pretty hard to get them through. The driving bands took a beating to make me think if .001 over the groove might be excessive. I found a ~.3577-.35785 cast and it took just finger pressure to get it through with no flattened bands. The bands on the larger bullet weren't completely flattened but the amount of hammering with a 4 ounce ball peen got me thinking. Maybe .357 in a .357 groove will be good enough. BHN is 10