I think your thinking of sliders, but you got the concept wrong
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No, Sliders was a nineties series; there was a much earlier one (seventies? early eighties?) and it was about a boat of shipwrecked people who get stuck in the Bermuda Triangle. The dude with the ray gun (he stole it from some alien early on, and it was the only weapon that they had, then they all got split up as well) looked like John Hurt (may have even been him).
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Oddly enough I think I read about this show, it was in the 70s, and they were on this place connected to parallel universes.