Re: Driving an AR, dry firing problem?
I have seen this with my AR10 type rifles. Unlike a bolt rifle, the hammer is hitting the rear of the bolt directly, especially when there is no round in the chamber to neither absorb the firing pin hitting the primer. There is also no cartridge in the chamber to take up any small tolerence in the bolt lock up. The inertia of the bolt getting hit directly by the hammer is magnifying the impact of your hammer. If it still does this when you put a dummy round in the chamber, check the alignment of the trigger assembly and whether the hammer is hitting the firing pin squarely and centered. Some trigger assembles have hammer springs that are too heavy. I use RRA Match and Geiselle triggers. They are perfectly aligned, and have good hammer spring tension.
"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt