How to model the Torsion of a bar in abaqus with displacement control?

Hi,

I have a bar with an analytical rigid surface attached at the free end with a RP at the centre of it. I am applying a rotational BC of UR3 = 0.017 (1 deg) with respect to the Z axis, but the resulting rotation at the end of the bar is more than 1 degree. Any idea why? Or how to have a full control of the twist of the bar? Also the bar deforms in shape where the end at which the twist is applied expands, making this cross-section bigger (clearly no the deformation expect for torsion). Input file attached in a word doc. 

I will work out the torque generated to produce this rotation.... to plot the torque-twist relation.

Thanks a lot,

Kike