# Ammunition Case Design and Its Impact on Functionality Cartridge case design plays a critical role in how ammunition functions within a firearm system. 9mm ammo uses a straight-walled, slightly tapered case that supports reliable feeding in handgun magazines. .223 ammo uses a bottleneck case design that improves gas pressure management and feeding reliability. .308 ammo ... https://bulkammotogo.com/product-category/bulk-rimfire/