The PBS repaired a bunch of different items including small arms. As was said above they were the main supply point during the Italianicon campaign. They'd go in after a battle, collect the discarded items and then repair them. So that rifle went through the repair at the PBS in May 1944. Most likely cause to go through I think would have been damage during battle or it was worn out and rebuilt. I have a Dec. 42 barrel with PBS 10-44 stamped on it just like yours.