Automatic rifle beginning to oddly jerk (7)
I believe the answer is:
robotic
'automatic' is the definition.
(robotic can mean automatic or mechanical)
'rifle beginning to oddly jerk' is the wordplay.
'rifle' becomes 'rob' (rifle can mean to steal or rob).
'beginning to' suggests taking the first letters.
'jerk' becomes 'tic' (jerking movement by the body).
The initial letter of 'oddly' is 'o'.
'rob'+'o'+'tic'='ROBOTIC'
(Other definitions for robotic that I've seen before include "Stiff, unemotional" , "Automaton-like" , "Like automatic device" , "Like a mechanical figure" , "Like the Tin Man" .)