It appears that both M1s are being fired. Notice the dust in front of both muzzles. I think I see two spent casings in the air - one right above the receiver of the second rifle and one straight above the first rifle only much higher - around 2-ft or so above the first rifle. That one is questionable because it is also in line with the hillside and could just be part of the hill. Nevertheless, it looks as though both rifles have just fired nearly simultaneously.
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