It can be made to fit certain cans like the SPR/M4 or 12th with pretty much all midlength rails. An 11.5" barrel cannot do that. It gives a nice boost in velocity which raises the range at which fragmentation no longer occurs by a huge amount over say a 10.5" barrel. Its short enough... yet long enough. I have an 11.75" barrel, not a 12.5" which is gaining popularity. The length is just to fit my suppressor and rail combination.