HELP. I have no idea what this thing is or if it is even firearms related!

So, I have this 92 year old grandmother. Both of her husbands and 2 of her brothers were all in the service. 3 of them were on the beaches at Normandy. She has had her house for about 50 years so tons of stuff has just piled up in odd places like in her basement (I have found books from as early as 1902 down there).

Today I picked up this thing thinking that it was nothing then looked at the bottom and noticed what appeared to be a primer. A little closer inspection revealed the writing partially covered up by a metal band which reads "CASE CARTRIDGE M169". There is also some stuff that I can barely make out that says something like "40MM PM430 MA-94E055023".

This is a pretty exciting find for me and I am trying not to get my hopes up that it was my grandpas. I included a couple pics that I took from my phone. I am thinking that the metal band locked more of these together. Any info would be greatly appreciated.

Awesome. Thanks for your help. What I have found on the net says the MK19 first saw service in 1967 in Vietnam so I have no idea where it came from. I do have an uncle that went to Vietnam but he is from the other side of the family. I will have to give him a call.