Like John I have had several Roberts rifles with long throats...and can add on top watching friends work loads with a few others. Most of mine had 22-23" barrels.
I have seen about the same thing he has with the 115's,and velocities in excess of 3000 fps. 120's did about 2900+,about what we see from a 270-150.
100 gr bullets went 3150-3200.
Comparing this stuff to data for the Improved I never got around to the Improved version.
