There is a difference. 338-06 3.340 COAL 338 a square is 3.440 COAL. In many 338-06 chambers 338 a square will not chamber and if it does could increase pressure due to the fact it is close to the lands.
Another point many rifles will not cycle 338 a square - rugers being one example. If you are wanting a 338-06 or a square consider that you will need to cycle 3.440 length cartridges.
