I just did my 686SSR hammer. Here are the before & after weight stats:
stock hammer: 32 grams
after stage 1 hammer bob: 20 grams
after stage 2 & 3 grinding: 16 grams
So we have a 50% weight reduction for the completed hammer. Used 1 Dremel cutoff wheel, a bench grinder for rough grinding, carbide Dremel grinding bit for the small areas, and 220 grit on a cheapo Harbor Freight 1" belt sander worked wonders on the final finish.