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I have noticed this similarity of the back part of the tongue position of ж, ш and r. But the front part of the tongue is in different position. Can go seamlessly from ж into a kind of r and back,...

Russian ж is not the same as 'zh'. And ш is not really 'sh'. You have to really listen to these by native speakers for a while. Then you get it, that the tip of the tongue is doing something...

Various recorded pronunciations are on the masterrussian site, and other sites listed in 'resources' section.
http://russianlearn.com/pronunciation/category/rule_3

also individual words:...