"Thanks for the info Mike. But I also thought the "A1" was also the designation for change from filler hole-screw plug bodies to solid bottom bodies?
I'll be waiting & hoping you or someone will find definite facts about change of nomenclature for practice grenades MkIIA1 to M21. Either way I really think the change to M21 was done sometime late '43-early '44 to prevent confusion between live and practice grenades....a logistics oriented change.
From "Rifle and Hand Grenade Research and Development, 1945 picatinny Arsenal"
The Mk II grenade body with the MlOA3 fuze was designated MkIIA1 to distinguish it from MKII bodies equipped with previous fuzes such as MlO, MlOAl, and M10A2. Some of these MkII grenade bodies contained a tapped hole and a metal plug in the base while others had a solid metal base. The decision as to whether the plug was used or not was optional with the manufacturer.
As to the date the designation switched from the MKII Practice to the M21, it appears as it was changed around the same time the MKIIA1 designation came into play
The practice hand grenade, M21 equipped with hand grenade fuze, Ml0A3 was the latest approved model of this type.
This time period would be Oct 1943 - April 1944. We can suppose this by knowing 3 things:
1. The procurement of the M10A2 hand grenade fuze was accordingly terminated October 1, 1943.
2. The MKIIA1 grenade with M10A3 fuze and loaded with EC Blank Powder was reclassified as "Limited Standard" and the MKII TNT Loaded (which would have used the M6A4C fuze) was classified as Standard on 6 April 1944.
3. A limited procurement contract of 6 million units was placed in June 1944 for a developed grenade designated the MKII (TNT) with hand grenade fuze M204 (T2E1)."
This answers a few common questions, and explains the rarity of M6A4C fuzes.
Edited by 917601, 11 July 2019 - 01:45 PM.