Hi Yana,
I had an Osprey Supertarget and compared to my Mk3 Supertarget rifles I also noticed that it was positively rough to shoot.
The Mk3 is a much nicer Supertarget to shoot but I have not worried too much about the reasons why - I just sold the Osprey and kept the Mk3 Supertargets .
The new owner of the Osprey Supertarget is delighted with it - but has not compared it with a Mk 3 - yet!