Hello Oleg

I am precise that the bore diameter is .433.
This is the grove diameter.
I still have the slug I pushed through the bore.
My bore shape is not the same as yours.
the rifling is quite thin, not like what you find on todays type of guns.
I only own one other drilling a Franz Kettner with similar type of rifling.
I have not counted the lands.I believe it has right hand rifling.
I have found a company here who casts custom bullets as large as .432 diameter.
The prices of the bullets do not break the bank.
I can give you their webiste if you are interested.
thanks
Ralph