First thing most people do not realize is that crossbows are just another piece of archery equipment. They basicly have the same effective range as the other style bows.

The average safe distance for a crossbow is 30-40 yards. Beyond that, you are giving deer too much time to react to either the sound of the bow or the arrow, this can casue a bad hit. Now with slower animals like Moose, you can go a little further in distance.

God luck.