For a long time the 11.5 was considered a more reliable barrel length, plus it had the additional velocity for fragmentaion. The main reason the 10.5 stuck around was because of the military using it. Now, things have changed a bit, and the 10.5s are pretty squared away.



Paul from BCM has mentioned in the past that the 11.5, with its extra inch of barrel past the gasport, retains a 40% longer dwell time than the 10.5". I think you start to really see this become important as weapons get dirty, temperatures change, weaker ammo is used, or other things come into play.