I just installed a cantilever type rifled slug barrel onto my Mossberg 500 20ga. I shot the first shot at the target starting at 50 yds, the gun was shooting in the dirt. I have since raised the crosshair adjustment so much that it is out of adjustment and it is still shooting 5'' low at 50 yds. The barrel came with the scope already mounted on it and it said it was laser bore sighted. I have mounted plenty of scopes but have never had this problem. any help would be greatly appreciated.