Here are pictures of the Falling Block breech block.
Front and side rear view....Notice the integral bottom
extensions are narrower than the top. These are
what the linkage is inside of and when breech is
levered down these fit though the slot in the stock.
And being narrower the slot isn't too wide so the
stock has enough strength. Botton extensions same
width for all action sizes.Just top different
for the size of action needed for big cartridges.
This breech is little rough as it has had a dozen
changes to it. But it holds a load in 4 bore
of 1500gr over 2600.Ed