I don't have anything larger than .30. Well .312 and .314 for brit rifle but all too small for 3/8 brass. If I don't like the 1/4" i have ordered I will get the 9/32" 4060May mentioned. That would be ideal.Trying tobslug a .30 with wood is a bad idea, period. Not so much if using oak, larger calibers, and cutting it into short sections as has been mentioned. All I have larger than 1/4" brass is 3/8" all thread rod wrapped in tape; this is what I use for the larger calibers. The only large dowels I have access to are crappy angle-sawn birch.