The extractor is the weak link, its a rim fire essentially and the modification will cause it to break in a short order. The real crux then is finding an extractor for 20 year old rifle that isn't made anymore.The Cooper Model 38, 17CCM rim measures .309. The rim on the 17 Hornady Hornet measures .350. Is it possible to modify the bolt face on the CCM to fit the 17 Hornady Hornet.
Possibly setting back the existing barrel and re-chambering or chambering a fresh barrel.
Thanks, Bill.