... stop worrying. The Lake city appears to be way past its "Bang by..." date. The dropped shot in the Federal group is probably "driver error" caused by the usual difficulty of seeing exactly where the tip of the blade is, especially if the light is varying. And the Hornady group is just fine. You need to shoot a lot more to decide which type of ammo has the edge.
Permitting ourselves to overlook the low shot on group 2 as anomalous, we have a service rifle that shoots 2 MOA at 100 yards. And the cases look OK to me. The case neck sits in the front end of the chamber, not the throat. So I don't see how a worn throat can hurt the cases.
And from my own practice and competition experience with an M1917, you are not going to get much below 2 MOA with a service rifle unless you have 1) perfect vision or 2) use a scope.
You appear to have a fine service rifle. It would be a grave error to re-barrel it unnecessarily.
SO DON'T WORRY, BE HAPPY
just practice and enjoy!
P.S: If the throat was seriously worn, all groups would be lousy. So it isn't.