 In the mid-to-late 19th century adjustable metal time fuzes, the fore-runners of today's time fuzes, containing burning gunpowder as the delay mechanism became common, in conjunction with the introduction of rifled artillery.Rifled guns introduced a tight fit between shell and barrel and hence could no longer rely on the flame from the propellant to initiate the timer.The new metal fuzes typically use the shock of firing ("setback") and/or the projectiles's rotation to "arm" the fuze and initiate the timer