See the below article about the implementation of a new procedure in the San Diego Police Crime Lab. Soaking fired cartridge casings has yielded better results in obtaining usable DNA, though implementation remains a problem.
https://www.wired.com/story/a-new-method-of-dna-testing-could-solve-more-shootings/
Additionally, see the resource below: “Identifying the Factors Necessary for Successful DNA Profiling From Spent Cartridge Casings”
https://www.ncjrs.gov/pdffiles1/nij/grants/251819.pdf