I am curious how the GIs shot the Garand at night during WWII and Korea? You obviously would not want to mount a flashlight to it (bullet magnet). You could not get tritium sights or red dots. Did they just point shoot the gun?
The technique taught was to lay the front sight onto the target, looking over the rear (peep) sight. This was still being taught in Army Infantry training in the 80's with the M16, and probably still is. I haven't hear the white string technique before but it sounds clever.
In Korea many attacks were so close that aiming wasn't necessary. One account in the GCA Journal recounts a night where an Army unit fired so many rounds through their Garands that the front handguards were charred. The M1 Carbine was less popular in the extreme cold, because the action is not as reliable under those conditions.
The weapon of choice for night patrols was the Thompson submachine gun, for obvious reasons. Or the Schmeisser on the other side.
In a defensive postion, when possible, machine guns are tripod mounted so elevation and angle can be set precisely. Otherwise, firing stakes are set in the ground to define your sector of fire. Trip wires, trip flares and noise makers (C ration cans filled with rocks for 40 years) were set up in likely avenues of approach.
Hand grenades are much preferred because they do not reveal your position. New troops would learn very quickly not to fire in response to a probing attack. Prepared night attacks would try to fire flares behind your position, so you were silhouetted but they were not.
An Army study found that 75% of all combat is at 100 meters or less, and 95% is at 200 meters or less. Almost all Army tactical training is at night.
You can make yourself mighty small at 100 meters. In a famous attack by the 1st Ranger Battalion against an Italian fort, the Rangers low-crawled across a field. Although discovered, the Italians failed to depress their fire enough and shot over the heads of the disciplined Rangers. When they reached the fort and rushed it, the Italians surrendered almost immediately, believing themselves to be overwhelmed. Unfortunately, this same Ranger Battalion was later ordered to attack a German Panzer Brigade, which they did, with nearly every man killed or captured.
The 6th Ranger Battalion also low-crawled undetected across a wide field at night to liberate the POW camp holding the Bataan survivors. Aided by an Army Air Force plane overhead which distracted the guards.