Welcome gentlemen to the FTF, How about stopping by "Introductions" and say "Hi"?
Good schematic sicko! Based on what the OP has written, part 880 is not stopping the cylinder.
That could be that spring 881 is not working, or part 880 is broke or part 908 is broke.
Part 881 keeps pressure on part 880 which is moved by part 908.
When cocked, the trigger lower portion is moved forward releasing part 880, and spring 881 pushes part 880 up, thus stopping the cylinder.
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