If anything revolvers are probably somewhat more mechanically complex. Still, my experience says, given well maintained handguns, the odds of mechanical failure are probably about the same between revolvers and semi-autos. Feed cycle reliability and ammo flexibility are higher on the revolver though. Since cycling is purely muscle powered you don't have the same issues as a firearm reliant on recoil or gas to cycle. In exchange though you gain bulk and lower capacity. TANSTAAFL.