Rupture

While we don’t know for sure, there can be assumptions of what Rupture was. From the looks, it appears to be a Shatter with less reload time, so it would upgrade from the Shatter at level 60. It has a trapezoidal barrel, then another one just upside-down, then finally a thin rectangle. It supposedly was a Shatter with less time to reload, making it for a good bullet spammer.