Either one will work from BPI. I use the 3.5" but one of the users on here gets good results with the 3". he posted his load and components from BPI. If they say out of stock on the website, I called them and the dude said they fill from orders on the web first, so order them to get in line. I ordered mine and they were here in 2 weeks. There are several "recipes" on here for you to start with.