M1As and Garands are shot in HP Silhouette in the "Iron Sights" class.
In the case of the Garand, all you need is to make sure you load no more than 5 rounds per bank of silhouettes.
With the M1A/M14, you must have either a 5 round magazine, or if using a 20 round mag, avoid resting the base of the magazine in the palm of your hand, holding the rifle from the fore end.
I shot my M1A a few times and found that if the silhouettes are placed in a beam, you can align the top of the front sight with the beam underneath as a point of hold... Best of luck,
Joaquin B.