The weight you need at the end of a drowner,depends on the type of bottom you have.
A hard bottom requires much more weight,than a mucky or muddy bottom.I have had beaver swim 100 feet along the bottom,after breaking the wooden top stake,this beaver pulled along a full cement block,which weighed well over 50 pounds.This was on a hard bottom,the same weight was more than enough ,when used on muddy bottoms.
The last 7 years,I have not had to worry about beaver drowning weights.I have switched gone to 330s,I sure don't miss hauling or fooling around with drowning weights.
Tom