I checked the archives and found the McMaster Carr part numbers for the replacement recoil springs (9637K65) and buffer material (8789K32). Checking with McMaster Carr, they need to know what Durometer is needed for the Buffer material. 40A - Medium Soft, 60A - Medium Hare, 80A - Hard, 90A - Extra Hard, 95A - Extra Hard, or 75A - Extra Hard. Any help will be appreciated. Machinegun Charlie