Does pointing your gun up or down affect its accuracy? The answer is “maybe” according to a recent US Army Armament Development, Research and Engineering Center (ARDEC) presentation released at the 2017 National Defense Industry Association small arms conference. The presentation covers a study conducted by ARDEC which examined the effect of ullage (free space in a loaded round) and orientation on the consistency and velocity of small arms ammunition.
The findings of the study may not be exceptionally surprising – it turns out that rounds with more ullage are less consistent – but they are remarkable in how detailed they are. The ARDEC team testing followed standard EPVAT procedure, accounting for pressure, velocity, and and action time (the time between ignition of the primer and the bullet leaving the barrel):