There are two systems in blogspot, the old one and the new one (was previously beta). To verify, you need to visit to see if you get a XML or a web page.
In the list below, the first three url is the default for sitemap but in the new system, it is redirected to feedburner and will not be recognized by rss readers. If that is the case then use the last url for the feed. If it still provide the xml format then you can still continue to use those urls.