As to Saving Private Ryan..there were factual and continuity mistakes but they did not detract from my enjoyment of the movie. Same goes for Kelly's Heroes.
After a bit of surfing I did, however, find this:
"During certain scenes in the movie, we see Jackson switching his Weaver M73B1 sniper scope on his M1903A4 sniper rifle with a Unertl sniper scope. The problem is that the Unertl scope was used exclusively by the U.S. Marines in the Pacific Theatre on their M1903A1 sniper rifle. Even if we accept the premise that the Unertl scope was a 'battlefield pickup', the mounts for the Weaver 73B1 and Unertl are entirely different. The Unertl mounts require modification of the upper handguard, and drilling and tapping of the barrel for a forward mounting block. In the bell tower (and other) scenes, it is clear the rifle has a stock upper handguard. Therefore, it could not accept the Unertl scope."
Carry on.