I have no idea what effect the smaller bore will have on pressure.
Or what size 10.08mm vis 10.4mm might be.
We measure in thousandths of an inch.
I have no metric measuring tools.
But if the hole is drilled straight through from end to end?
It will be a cylinder choke.
Choke only works when the shot column is squeezed down suddenly just before it exits the muzzle.
The trick to a choke is to have the shot column exit the muzzle while the shot is still being compressed toward the center of the column, but before it starts rebounding back away from the center.
Consider a water hose nozzle.
If the hose doesn't have a nozzle constriction on the end, there is no constriction to make a stream.
Doesn't matter what size hose the hose is.
If you want it choked, you could
jug choke it by reaming a larger bore just behind the muzzle and leaving the muzzle what the rest of the bore is.
http://www.brimstonepistoleros.com/gazette/apr05.html
rc