David:
That was my understanding also. The mortar stayed at a 45 degree angle and the powder charge determined the range. That is why I am puzzled by these drawings showing the way the mortars were mounted on the mortar schooners. They were mounted on a record-turntable looking thing called a mortar bed, which obviously was designed to be turned by cranks to point the gun toward the target. But there was also a long segment called a "mortar slide" on which the mortar also could go back and forth on the mortar bed.That is the part I'm having trouble understanding. It may be that the purpose of the slide was just to help absorb some of the recoil from firing the gun, much as the movement of a naval gun carriage did. If anybody has any other ideas I'd sure be glad to hear them.