I've always been baffled by the move away from gun armament on US and UK aircraft post-WW2, it always seemed to me to be a retrograde step. Did the Soviet aircraft design bureaus follow a similar philosophy? I know that in later years they had selectable speeds for the cannons on the likes of the Su-25 for A2A or A2G.
It certainly came back to bite the US on the posterior in Vietnam; I seem to recall Big-Gen Robin Olds saying that he could've shot down an additional 9 MiGs in his F-4 if it had had a gun (I think it was in an episode of that classic documentary series Reaching for the Skies). If nothing else, bullets (cannon shells) are far cheaper than missiles!