Having the right eyewear is critical to ensuring the best possible protection. While most lenses today are made from polycarbon materials that will stop most flying debris, it does not mean that the glasses as a whole will provide sufficient protection from bast or even shotguns. The Army rigorously tests it's eyewear to ensure that they are rated for the types of conditions found on the battlefield. Ultimately I would argue it's worth the cost to save you and your team's eyes.
Below is the APEL from PEO soldier. The link is: http://www.peosoldier.army.mil/docs/apls/APEL-poster.pdf