Hmmmm.... A bit more research makes me rethink my earlier post. Check this out:
http://www.odcmp.com/Forms/M1917.pdf Apparently the U.S. government and the troops didn't think much of the M1917.
Depending upon when he entered service, GGF might have used one in training, but more likely he used an M1903 Springfield, M1 carbine or an M1 Garand by WWII.
Roger, you might have an M1917 that once belonged to your GGF, but it is looking pretty unlikely it is a weapon he carried in WWII. First, the troops did not bring their issued weapons home after the war. Many brought home souvenir weapons they captured or purchased from other GIs, but the issued weapons went back to the arms rooms. I doubt your GGF would be so in love with an M1917 to risk court-martial to bring it home.
I've never seen an M1917 in WWII ETO photos and have just started researching Saipan and Tinian for a Sherman project I'm working on, so though I know some units in the PTO were using some old equipment, I'm not so sure an M1917 would be in use much beyond the first year of the war, much less as late as June 1944.
I am curious to know if anyone has any better info?