Regarding the possibility that the frag is from a limber chest that got struck by a shell, exploding the chest...
I've been emailed six close-up photos of that frag. Here's a slightly shorter version of my email reply (rather than the micro-detailed version):
1- Most shells whose internal powder-charge did not explode (but are no longer intact) look "broken" instead of "fragmented." Meaning, due to external force rather than internal force, the shell's body breaks into fewer pieces. For an example, see the photo below, which shows a 2.9" Read shell that apparently impacted onto a large boulder on South Mountain, and broke almost in half.
All of the sidewalls being missing from the Vicksburg nose-frag indicate its internal powder charge exploded.
2- Paper timefuzes were not inserted into shells until moments before firing. So, the shells in a limber-chest or caisson wouldn't have the paper fuze in them. If the frag's corroded zinc Parrott fuzeplug has any remnants of a paper timefuze in it, the frag is from a fired shell, not from an exploded limber or caisson.
That being said, there are three possible explanations when there's no trace of a paperfuze:
1- the paperfuze rotted away entirely.
2- the shell exploded and the blast caused the paperfuze to be "spit out" of the fuzeplug.
3- the shell was in a limber or caisson which got hit, causing the no-paperfuze-in-it shell's bursting charge to explode.
In other words:
Digging the gunk out of this frag's fuzeplug and finding remnants of a paper timefuze tells you that the frag is not the result of an exploded limber or caisson. But unfortunately, finding no paperfuze remnants cannot tell us whether the shell was in a limber chest that got hit, or is a fired shell.
I should mention... the six photos I've seen, each with a ruler alongside the frag, show it is indeed a .3.67" caliber frag, so it is excluded from being a Dyer frag.
Regards,
Pete