If you clean the barrel, the first shot or two will change point of impact. This also happens if you shoot different ammo through the gun, the point of impact will move and eventually stabilize at a new point of impact. I notice this with my 22's, one of which is a CZ bolt action. If you don't realize this, it can have you chasing ghosts for a while with scope adjustments.
Also, check the tightness of all the screws after you shoot it for a bit. First time out, things can loosen up and before you know it, the scope has slid on you.