Variable and Magik have it right. Yes, there is a loss in velocity, and because of that, longer distance accuracy may suffer, but I've shot that 11" to 300 yards with solid hits on poppers and that's good enough for that package. Most of my shooting and training is of the CQB persuasion as I feel that is the most likely situation where I might have to use such force. Run through a live fire house during a clearing exercise a few times and then the beauty of the SBR comes immediately to light. I think it's easier (faster) to pick up targets with it as well.
I've talked with an instructor @ TDI about the SBR thing and he stated something like this: The bullet only needs to make contact with the barrel over a few inches and that sets the course for it's general accuracy. He mentioned some guy who can shoot a snub nose revolver to 200 yds accurately. He's a very knowledgeable person, lives tactical training everyday of every year, and you've probably heard of him. That being said I don't think he has any reason to lie to me. At any rate my shorty shoots great.
This is a target from this past weekend. An IPSC target 100 yds, prone, firing about a shot a second. Optic is an IOR 1.4-4x, set on 4x, first time it's been zeroed and used, S&Bm193. Not bad for a short battle rifle.
I must note that my XCR is and has always been heavy compared to my other SBR's, and now with that IOR it's 10.5 lbs, unloaded (weighed on a bathroom scale).
I recently bought a 9.25" POF gas piston upper. Can't wait to see how that shoots. Such a compact package.