Most excellent work!
Looks great as is so you can stop now. But if you want to tweak it some more, I'll add a couple of suggestions:
When the toggle is fully retracted the rear toggle should just come into contact with the rear of the frame. Looks like about a 1 mm gap.
Like the smoke effect! How about adding smoke coming out of the breech and empty shell casing?
Is it possible to create an option for a frame-by-frame advance?
cheers,
-- Dan