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Gunner was pretty close!

He originally thought the picture below was two grenades in a display. It was a blow-up of two grenades, and a launcher, in a display.

On the left, an uncut US Vivien-Bessiere grenade. On the right, a cut-away French V-B, behind, a US 'tromblon' V-B launcher. You can tell it's US because it twists to lock around the front sight, vice the French launchers, which slip on straight and use a locking ring. In this case (not as obvious) it's for a US M1917 Enfield rifle, and was a Chateau Thierry battlefield recovery.

If you've the time or a fast connection, here's a high-res shot.


I notice that the inside of the case has indentations(?) in it to help with fragmentation. You mentioned earlier in your blog that the pineapple look was not the best way to get fragments if I remember correctly. This has the inside pineapple look. Is this contact detonation or a burning fuze activated by the metal sliver that seems to be attached to the round in the center "tube"?
The way that iron fails under pressure, the overall structure of the iron, and the amount of pressure determines the fragmentation effects. Good eye Gunner. External patterning does not improve fragmentation - *internal* does. I can't explain the full metallurgy of it - cuz I don't know it - but essentially, if the 'weakness' is on the inside, the iron tends to crack along those planes - especially if they were cut into it not cast. Something about how the iron is structured means that it doesn't work the same way when the weakness is on the outside of the blast vessel. I'll explain the rest in the post I'm putting together for this weekend.
Is the round out of the barrel supposed to catch the thing and fling it at the target? If so that is so weird. It seems like that metal tab would cause it to be innacurate, based on whether it was bent over too much or something like that. I understand the fill fitting part, although its sort of odd to me, but that brass fitting is the fuse then? Interesting rig that's for sure.
All will be made clear this weekend (if I don't have to work this weekend, anyway...) 8^(
If I recall correctly (Master Gunner Ian Hogg on grenades etc), the original Mills bomb had the exterior lumpy bits for enhanced grip in muddy conditions; it was known at the time (c.1916) that exterior grooves had no influence on the explosive formation of fragments. (The reference book is 30 years old, and buried in a box, ie. details unavailable.) Cheers JMH