Exactly...
Would be something of a downer, if one during a heated situation missed and hit a hard surface, making the cap crack and fly of with the weight, which effectively would make the baton worthless as a weapon.
The only reason i could see for the screw cap solution, was if it should be used for directing traffic as well. One could remove the weight inside, and thereby point it much longer...before the arm falls off.
But swinging a baton in highly trafficked areas, really wouldn´t be necessary until later (i assume), unless they had police control horsedriven traffic in the biggest cities already back then?