Some companies make their flash holes smaller than others, and Ruag must be one of them, since you're having that problem. For brass with the smaller flash hole, I simply use a Lyman Universal Decapping Die (the old style, that uses the small decapping pin). If you don't have one, you can try making your decapping pin smaller, but it's hardened steel, and it will be difficult. It also won't be as strong, once it's thinned down.
Hope this helps.
Fred