Ran about 1000 through this one since new and it has developed a dent. I inspected my P229 hammer and that too has a dent with thousands of rounds through it. So now i'm not that concerned about the 556 dent.
I'd be a lot less concerned with a dimple on the hammer face than I would the very real possibility that if the steel is soft enough to dent from FP contact, the sear surface could very well also be wearing to an unacceptable level.
Remember that the metal of the hammer is probably only surface hardened. A hammer still has to take the strain of the impact at the face of the hammer. This strain is then transmitted down the hammer at a angle to the pin. Therefore the ineternal metal fo the hammer needs to be softer and more complient under load.
The metal of the hammer is clearly an investment casting. My dimple is actually off center of the firing pin. If I didn't know anybetter I would guess that it is mark left by a hardness testing machine. Something like a hammer has to be hard on the firing pin face and around the pin, but you would not want it through hardened as the odd angle of the load would result in fracture.
It could simply be a dent, but if not, I would guess it is either by the design requirments of the metal, or the mark of a hardness tester. Many military guns throughout the world have these marks. Even RUGER has had to leave dimple marks on their investment castings from time to time to double check a "suspect" batch of receivers after heat treating.
I would only be worried if the divit or mark was at the angle on the rear portion of the hammer face. This would indicate steel that is soo soft, that the action of recocking dury recoil shows the metal is being "rubbed" away byt he harder metal of the bolt body. Also, if the hammer face was too hard it would not act as a "shock" absorber and would break like glass.
I had the dimple in the hammer on my SWAT model. I called SIG and explained it to them, they said it was not normal, sent me a UPS call tag for the rifle - OVERNIGHT AIR. I sent the rifle on the 8th of September, received it back on the 19th with a new hammer. Very nice turn around.
No real explanation, just "replaced hammer, tested for function". I would have been nice if they just sent me a hammer. I am not a gunsmith, but I have built a coulple of AR lowers and I think I could have replaced the 556 hammer in about 5 minutes.
Anyway, I have the rifle back and plan to function test it myself tomorrow. :twisted: