wouldn't the mortar just slide down the tube as the ice mels and nestle at the bottom?.I thought it (mortar)needed to be dropped to trigger the firing pin/cap.
I'm not an expert on launching mortars (I have only seen them launched in my general direction on occasion...LOL). I just know the intel folks told us last summer they were packing ice in those things and delaying the launch so that they could get out of the area.