Emulating the deep growl of Black Sabbath's 'Iron Man' is one of William Shatner's newest challenges on his upcoming 'Seeking Major Tom' album. While the finished version of the former Captain Kirk's take on the classic metal anthem has been available for streaming for almost a month, a video featuring Shatner laying down the vocals has just exploded on YouTube.

Former Ozzy Osbourne and Black Label Society guitarist Zakk Wylde helps Shatner through the vocals (in addition to adding some stunning guitar work) but his efforts aren't heard in the video below. For the most part the actor gives an a Capella performance of the song. It's a fascinating clip -- over 300,000 people in three days agree -- during which the singer doesn't break focus to offer a smile. It's clear he takes his music as seriously as his acting.

'Seeking Major Tom' offers plenty more classic rock songs in Shatner's signature spoken word style. When it's available on Oct. 11, fans will hear his take of songs like Steve Miller's 'Space Cowboy,' Queen's 'Bohemian Rhapsody' and U2's 'In a Little While.' Guest artists include members of the Allman Brothers Band, Alice in Chains, Asia, Deep Purple, the Kinks, the Scorpions and the Strokes.

Watch William Shatner Record Black Sabbath's 'Iron Man'