Why does Tim take the brown bess from Sam?

Tim's reason for taking the brown bess from Sam is
two-fold.  First, he takes the gun in the hopes of preventing Sam from joining the
militia (having a weapon was a requirement for joining).  He wants to prevent Sam from
being in harm's way and to force Sam to come back home and stop arguing with their
father.  Second, Tim knows that the brown bess is necessary for his family's survival. 
Mr. Meeker needs it for both protection and to obtain food.  Without the brown bess the
rest of the Meeker family will suffer.