I find copies of the Handbook in both German and French onGoogle, but have not had time look into them in detail. If Scharnhorst was using two wall targets to assess effect in depth that would be insufficient to illustrate the beaten zone. Given the extent of his Hanbook, I think it is a fairly broad survey of the existing experiments, so I have the impression that the concept did not exist then.
I also found a French manual from the 1830's for artillery officers. It is quite detailed and has a nice section on ballistics with a good bit of math. It is very worth downloading for anyone interested in such things, but it didn't address the subject of how cannister performs.
I'd like to find something about the impact area of shrapnel shells,