Sometimes the larger diameter brass brush pulled into the separated case works. sometimes it doesn't. Best approach is the ruptured case extractor.
BTW, the conventional approach to reloading .303 British (full length case resizing) doesn't work too well with the generous chambers, headspace variances, etc. I found that I was getting head separations in three and sometimes only two firings.
A web site called "The .303 Page" or something like that discussed that. As a result of an article there I started neck sizing only with, of all things, the old Lee Loader kit. I got up to eight reloads from cases with it, doing one full length sizing about the fourth firing and watching case trim length. The only disadvantage was that cases needed to be segregated by the rifle they were fired in.
Otherwise you are going to get very good at extracting ruptured cases, because you will have a lot of them.
The .303 turns out to be remarkably practical and useful once you adjust to it. It doesn't adjust to you.