He didn't have any good solution.
He could only pin his hopes on his own handiwork.
Before carving the grooves, he decided to first draw their shapes with a pen.
He slapped his head and decided the barrel rifling would twist two full turns.
The broach would also need to rotate two turns during the cutting process.
This ten‑centimeter‑thick wooden cylinder should also rotate twice.
Its rotation would be driven by the groove on its surface, and that groove also had to twist twice.
He suddenly realized a problem: it would be hard for him to machine that groove to a precise standard.
So the rifling he pulled out would also be hard to make precise.
A lot of earlier effort might have been wasted.
But he felt he had to use his hands more, pour in more effort before he could find ways to improve.
On the side of a cylinder one meter long and ten centimeters in diameter, he needed to draw a spiral line that made exactly two full turns from one end to the other, with very even pitch.
