Modelled a 7.62x51 NATO round in Onshape. All dimensions should be accurate (apart from the bullet itself, as it varies). If it does not print well, I suggest splitting the model in a program like NetFabb and then gluing the pieces together.

The 7.62x51 NATO is a common round used in marksmen rifles and machine guns. In the L129 and L7A2 in the British Armed Forces, and the M110 and M240B in the US Military. It is an effective round in anti-personnel and being a larger round, deals more damage at further distances.

Have fun!