60mm & 81mm Mortar Rounds - WWII

Shown are the 60mm M49A2 HE round and the M69 solid cast iron training version. These were used in the M2 Mortar.
They weighed 3 pounds and had a maximum range of 2,000 yards, although accuracy was diminished at ranges over 1,000.
While having less power than the 81mm mortar, the 60mm was easy to transport and could be brought into action quickly, which was its prime asset.
The 60mm M2 was a versatile and reliable performer. A key infantry weapon during World War II.

Next is the 81mm M43A1 HE Round. It is the smallest of the high explosive shells made for the M1 81mm Mortar. It weighed 6.9 pounds and had a maximum range of 3,290 yards.
The heaviest of the 81mm types was the M56, weighing 15 lbs with a maximum range of 1,300yards. There was also 10.6 pound  type, designated the M45.

There were also White Phosphorus and Illumination rounds made for each caliber.

On both the 60 & 81mm, four small bags of propellant ("increments") were fixed to the fin assembly using spring clips. Those bags, left attached or removed individually, gave basic range control. Changing the inclination of the mortar tube provided fine adjustment.

The round needs to be of a precise diameter for proper function with a large enough an air gap to allow the shell to easily slide down the tube. Something is needed to seal that gap, when the the round fires, for maximum performance. The "bourrelet" feature provides the necessary gas seal. The bourrelet is a series of grooves machined into the wall of the shell body. When the high pressure propellant gas begins to pass between those grooves and the inner wall of the tube, air turbulence is created forming an effective gas-check. Without this feature, range would be significantly reduced due to lost pressure.

An ignition cartridge, screws into the tail fin assembly. When the round is dropped into the tube, it hits a firing pin at the bottom which fires the cartridge, forcing flame out the holes in the tail fin assembly, igniting the propellant bags.
Here is a 60mm round with its cartridge (yellow). The paper cartridge is a separate unit, which presses onto the primer base. At left is the primer for the 81mm round, next to a 12ga shotgun shell for comparison.
(Of course the ignition cartridge contains powder only.)

The PD fuze, M52B1 is the same for both the 60mm and 81mm HE rounds. There are differences in manufacturing details, most notably the material used, either aluminum or plastic. These have 1943 and 1945 dates.
The 81mm shell has a "adapter" ring used to mate the fuze. Without that ring, larger artillery fuzes will fit, but it doesn't look like that was the intent.

The rounds were packed in their shipping tubes ready to use.

M52B1 Fuze