The manual recommends any .45ACP ammunition. It even recommends +P and +P+ marked ammunition. There is truth to the P90 being able to stand up to that much pressure. No one's exaclty sure why Ruger did not go through with it. The P90 is an excellent pistol and is one of the best .45ACP's on the market. Rugged, reliable, accurate, priced fairly, and 100% American. Can't ask for much more than that.