U.S.
How “bump-stock” devices work
October 4, 2017 - The deadly arsenal of weapons found in a 32nd-floor room at the La Vegas Mandalay Bay Hotel included 16 assault rifles, 12 of which had been altered from semi-automatic to fire in automatic mode.
The guns included an AR-15 and an AK-47 as well as four Daniel Defense DDM4 rifles, three FN-15s and other rifles made by Sig Sauer.
The bump-fire stock increases rate of fire but can wear out the mechanics of a gun -- snapping the firing pin that was designed only for semi-automatic fire.