Life on MarsGoofs
The type of rifle that is in Sam's hands when it is kicked by his Dad changes. When he places it down when he goes to talk to his younger version on the boat it looks like a Ruger Mini 30. When he picks it up a minute later it has changed into a Ak-47 or SKS type of rifle, which is then kicked by his Dad and it seems to go over the side of the boat. That is a less expensive type of rifle, which may be why it was the one tossed into the water.