Improving Weapons with Simulation

As engineers design new weapons or modify existing ones, reducing time and money on development can be critical in providing soldiers with improved weapons without undue delay. A new sight may be planned for the M4 rifle, but how well does a prototype design work, and where would be the best place to mount it for the best accuracy and ease of use? Or new, nonlethal weapons may be needed, but will they perform as expected at different ranges?