SIG SAUER SWISS ARMS SG552 - Manual (Page 27)

When the third round is fired – just like the second round
– via the release bar, the segment (10), pressed by the
chargeover (14) jumps on the driving cam (12) of the
trigger (8) and interrupts the support of the trigger rod
(4) by the automatic fire pawl (11). The sear (5) catches the hammer (3) (refer to illu. 67).
The advancing bolt drives the release bar (2) downward.
The release bar (2) presses the sear (5) to the rear and
releases the hammer (3) (refer to illu. 71).
The hammer is retained by the trigger rod. When the
trigger (8) is released the segment (10) moves back to
its home position (refer to illu. 68).
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Function
When the hammer (3) is thrust forward, the chargeover
(14) presses the pawl (13) via its eccentric (15) on the
segment (10). The segment (10) jumps up by one notch.
The recoiling bolt cocks the hammer (3) which is retained
by the sear (5) (refer to illu. 67).
The advancing bolt presses the sear (5) via the release
bar (2) to the rear thus releasing the hammer (3).
The segment (10) moves up another notch.
Function
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illu. 71) Trigger system during firing (second round) illu. 70) Trigger mechanism after firing (first round) illu. 72) Trigger mechanism after the third round