I am trying to understand the Holmes design for the open-bolt
9 mm SMG trigger as described in the Home Workshop Guns,
Volume 4, but there is something I can't figure out. I hope
someone could explain this for me.http://imageshack.us/photo/my-images/844/holmes1t.jpg/
As seen in the first drawing the trigger house seems to be
ready for firing. The trigger is in its forward position and
one can imagine how the bolt has been pulled back and is
hanging on the locked sear. The trigger bar has engaged the
sear latch with its first notch.
Now this is how I imagine the firing sequence for shooting
off a single round:
By pulling on the trigger the first notch of the trigger bar
pushes the sear latch forward which disengages the sear from
the sear latch, enabling the bolt to push the sear downwards
and run forward to pick up a cartridge. As the bolt moves
forward, the trigger bar is also pushed down and disengages
from the first notch and moves so that the second notch is
resting against the sear latch. This in turn will let the
sear latch push up again against the bottom of the sear.
After the cartridge has been fired and the bolt is on its way
back, the sear will be able to move up again and since sear
latch is pushing against it, it will lock in place and not
fire a second shot. The trigger bar is still engaging the
sear latch with its second notch and if the shooter relaxes
pressure on the trigger, the trigger bar will retract and
once more engage the sear latch with the first notch.
What I don't understand is that in the drawing, the trigger
bar bump is located on the left side of the sear. It seems to
me that if the bolt is hanging on the sear, the trigger bar
would already have been pushed down by the bolt thereby
engaging the sear latch with its second notch.
What is it that I don't understand here?
For a clearer view of parts, see below:http://imageshack.us/photo/my-images/849/holmes2.jpg/