Photo 1 M724A1 TPDS-T round to the right of the M392A1 APDS-T.
Photo 2 closeups of the same.
Photo 3 differences in construction between the old design and the A1 version. The older design has 3 radial pins that retain the subprojectile in the pot, by engaging a groove in the tracer of the subprojectile. The pins will retain the projectile during the initial high pressure of firing, until the centrifugal forces cause them to retract, releasing the subprojectile. The newer design incorporates a mushroom shaped hollow chamber insert that is press-fit into the screw-in base, to cover the tracer area of the subprojectile. This hollow mushroom shape has a small hole to allow some hot combustion gasses to enter to ignite the tracer and to act as a pressure chamber to eject the sub-projectile, once the petals break off when the pot leaves the muzzle.The only difference in subprojectile seems to be the screw-in tracer as can be seen in photos 4 and 5. The bodies are exactly the same in length, taper, etc. Photos 6 and 7 show the differences in the carrier screw-in base, older design with pins and newer design without. The threads are left-hand. The pot consists of a pipe shape with the petals on the front, which this base piece screws into, holding the subprojectile tight against the insides of the petals. Photo 8 show both designs, the M724A1 shown with the mushroom in place in the middle and missing the mushroom on the right. Photo 10 shows 2 724A1 projos with and without mushroom.
Measurements Projo length rubber skirt to tip 267mm. The mushroom protrudes approx 17mm from the base. When the projo is resting on the mushroom, the rubber skirt is raised up approximately 10mm.
It is evident from the compatability of the components, that the improved version was designed to use as many of the older components as possible, eliminating the radial pins, but adding the mushroom chamber.
