For allowing current military personnel to purchase ammunition for their issued individual weapons (M16, M4, M9, M500).
The ammunition would cost the same as the government bulk costs, which is much lower than civilian-side costs. It would be maintained at military bases with the proper ranges for training. Ammunition wouldn't be kept aside, only credited to the individual for expenditure during voluntary-only marksmanship training.
Allowing this would greatly increase proficiency with these weapons, which personnel receive a lot less range time with than most people think. This would greatly increase our military's readiness, reduce costs of maintaining the force, and move money through the economy.
A point to keep is to never make this a unit-forced method to train cheaper.