There are 2 screws on each side like so: 0 represents a screw
Here's a rough measurement from my rail.
Bolt end_________________________________________Barrel end
|......0....... 0........cylinder/breech thing........0.........0........|
|- 0.3cm
|-- 1.9 cm--|
|------------------- 11.2cm -----------------|----2.5 -----|
|-------------------13.3----------------------------|-0.3--|
I measured it with my scope still on so dont take these numbers and go mill yourself something
but the inaccuracy of my scope is compensated by my using a precision photographic ruler.
So yeah. it's rough numbers, but should give you an idea.