In Lenny's former world, it was expected for an assassin to have incredible knowledge about their weapons.
In fact, many of them went as far as acquiring some blacksmithing Knowledge just to create their weapons according to their taste.
This was true not just for assassins, but also in some countries where people were allowed to carry firearms.
Many would customize their weapons according to their size, weight, balance, etcetera. Just to have a good advantage on the battlefield.
Lenny was also such a person. A weapon's length and even the grooves of its edges were all calculated and measured with precision and attention to detail for every strike and in many cases, created to maximize the use of certain fighting techniques.
Whether it were guns or blades, it was all the same thing. There were even many that crafted weapons specifically for targets.