it has to have the bolt of a magnum...
I did some testing sunday with the following loads in a 68cm barrel:
COL 99mm, bullet 300gr Lapua Scenar, powder Vithavouri N570:
92gr 853 m/s avg of two 3x group: 26mm
94gr 884 m/s avg of two 3x group: 21mm
96gr 911 m/s avg of two 3x group: 15mm...