C-14 dating worthless
The Copper Scroll is made of 99% copper and 1% tin. No organics. It is important to understand this. This lack of organics means that Carbon 14 dating can’t work. No living matter for the C-14 process to work on.
Stratigraphy is the simple idea of layers of dirt will lay down contemporaneously. So at 14″, for example, an ash layer is found, and all items found in that ash layer are from the same time period. The problem is that the Copper Scroll was found on a rock shelf. It wasn’t found in the soil. It has no peers buried with it. So there is no strata that can be claimed as contemporaneous.
Guilt by association
Scholar rely on the fact that the dead see scrolls found in cave 3 are quite likely the peers of the Copper Scroll. Therefore, the scroll is roughly 65 AD.
Handwriting on the Wall
There is a science of studying the changes in styles of letters and words over time. This science is known as paleography. Using paleography, scholars can nail down a small band of time where a document was written.
In this case, Frank Cross wrote a paper in 1962, “Excursus on the Palaeographical Dating of the Copper Document”. This paper made it into the DJDJ III, p. 217-21. Cross pegs the scroll ‘in the second half of the Herodian era’ and estimates AD 25-75. Another scholar, William Albright, wrote in 1960 that he dates the Copper Scroll between AD 70 and 135. Note that these two ranges overlap.
There is no shortage of disagreement on the dating of the scroll in academic, religious, amateur, and nut-case circles. Yet, most of these converge around AD 60-70 if they are averaged.