Cold bore shot 100 fps faster?

[pcso112]

Something new for me to ponder about this 300 Whisper. After having chronic problems with very erratic velocities in the subsonic realm, I decided to have almost five inches taken off my twenty one inch barrel. The gun is built on a Remington 700 action and is intended to be a dedicated suppressed rifle with a YHM Phantom 762.

I finally found the time to try the gun out again and I still had some moderately erratic velocities while using Reloader 7. The shorter barrel has certainly tightened the velocities up a little, but still not what I would consider acceptable. I also tried AA2015 for the first time and it showed consistent velocities after the first few shots. The problem I am having is the first few cold shots from the rifle with both powders have about 100 fps faster velocities then the subsequent warm bore shots fired. This is a new thing with the shorter barrel. I am accustom to just the opposite with my other rifles.

The velocities I had with the AA2015 looked like this
1087
1047
991
990
993
1003
977
979
973
983

Now I am far from an expert on any of this stuff. Can any one help explain what I have going on?