Hi Edbear
In the past I have swapped and changed barrels on HW35s and I always noticed that power went down about 1- 2 ft lbs when going from .22 to .177
Gerald Cardew went into the physics of this in his books and I believe he found that the transfer of energy to the pellet from the compressed air is proportional to the cross sectional area of the pellet. Hence .22 cal usually gives about 15% more power than the same rifle in .177
Most of my Airsporters in .177 are around 9 - 9.8 ft lbs whereas my .22 Airsporters are all over 10 ft lbs and a couple are up at about 11.5 ft lbs
John