The lbs of scrap copper that a 55 gallon barrel will hold depends on the copper type and whether it's shredded or granulated copper or normal copper wire or tubes.
Granulated copper you should be able to get around 1,000 lbs or more into the 55 gallon barrel or drum.
Bare copper wire the 55 gallon drum might only hold around 300 to 500 lbs of scrap copper.
A 5 gallon bucket can hold around 25 to 35 lbs of scrap copper depending on the type of copper and well packed it is in the bucket.
There are 11 of the 5 gallon buckets in a 55 gallon barrel so 55 gallon barrel should hold at least 385 lbs of copper depending on the type of copper and the density of copper.