I can run it as they come out of the box but will size these down to .356. Actually the bore diameter is the same for either a 357 magnum or a 9MM. But in the interests of slicker chambering .356 is what I size all the bullets I run in my Legend.Yeah. I found all of the book data I had to be grossly understating the velocities I was getting. I thought maybe I just had a “fast barrel” but I’ve had a couple 16 inch ARs in 350 and all were basically the same. I know of a few people using the 357 180gr, you’ll just want to work up slow since “technically” the rifle is made for .355 instead of 357. I know of a few people who just size the 357 down to 355, and some that run it as is.