five shot average was 2875 fps, with and ES of 71 and an SD of 27!
That tells me you have ignition problems.
Step up to a CCI-450 mag primer or even a CCI-41 (hotter still)
Second, I believe the Hodgdon Data web page (in print format) indicates 3,203fps from a 24" barrel. Figure ~25/30fps * 8" = 200/240fps slower.
You're not too far off from what I might expect from a carbine-length barrel.