Today I tried an experiment using mu usual fixed load of 58 gr of Wano PP with the Baco 400 gr money bullet, the COAL is 3.220" which lightly engraves the bullet.
I fired 7 shots, two foulers and 5 on the score target.  The first fouler went 1134 fps which I discounted from the ES results and got an ES of 6 fps. The average MV for the 7 shots was 1121 fps. 
Next I fired a further 6 shots with the same bullet and powder load, the bullet was breech seated .110" ahead of the case mouth engraving approximately half way through the base band.
The average for these shots was 1153.2 fps with an ES of 29 fps.  What I'm having trouble understanding is just why the MV for the breech seated rounds was approximately 32 fps faster than the fixed ammo.
As a matter of interest the group for the fixed ammo was 1.390" with the best four going into .960". For the breech seated rounds the group was 1.655" with the best four into .910".  The wind was from between 12  o'clock to 3 o'clock moderate, gusty approximately 10/15 mph, the range was 100 meters.
Mike

Hi Mick 
as per our phone conversation. By breach seating you have expended energy in pushing the bullet into the lands, the powder charge no longer has to do that. Hence that extra energy is used to increase the velocity