Despite its resemblance to a hand-grenade, your find has been proven beyond any doubt to be a World War Two era aircraft radio "trailing wire antenna" weight. The weight was on the end of a very long wire which functioned as an antenna that was fed out of the airplane's rear while in flight, trailing behind it, and the weight kept the wire more-or-less straight and prevented it from flapping around wildly. See the photos below.
More than just a couple have been dug in past decades, sometimes on civil war battlefields. The battlefield-finds mystified us for years, because the RTAW weight so closely resembles a grenade or artillery projectile. Precise weighing proved it was solid (not hollow), so it couldn't be a grenade... and there was no way to attach a sabot to it, so it wasn't an artillery projectile. Then one was found whose brass plug was marked "WT-7-A" which excluded it from being a civil war relic. (See the close-up photo below.)
SaintPierre, the -7-A marking is visible on the brass plug in your find. Welcome to TreasureNet's What-Is-It? forum, the best place on the internet to get mystery-objects CORRECTLY identified.
But why had several been found on civil war battlefields? Finally, an oldtimer recognized one, and the Internet showed that some are still being sold as what they are... an antique aircraft radio antenna component. (Seen for sale several years ago at fairradio dot com, where I got the photo below showing a fully-complete one with its wire attachment loop.) When one falls off an airplane, it doesn't care that it has landed on a civil war battle trench. That's good to keep in mind about a great many mystery-objects we dig.
