Components of drug delivery devices can experience large impact forces by a spring- loaded drive mechanism causing a drug reservoir of the delivery device to fracture. For an autoinjector having a reservoir, a plunger rod, a drive mechanism, and a carrier that experiences two impact events when the autoinjector is activated, the mass of the carrier and the mass of the rod is increased by a mass multiplier to reduce the impact pressure at both first and second impacts. The internal pressure of the device decreases in relation to a mass of the impact system 110 to force ratio, where the force is the drive force of the drive mechanism. To reduce the impact pressure from the first event, the mass of the plunger rod may be increased within a range such that the ratio of plunger rod mass to drive force is within a range of approximately a value greater than 0 kg/kgf to approximately 0.05 kg/kgf. To reduce the pressure of the second impact event, the mass of the carrier may be increased so that the ratio of the combined mass of the reservoir, plunger, plunger rod, and carrier to drive force is within a range of approximately a value greater than 0 kg/kgf to approximately 0.15 kg/kgf.
