I'm having trouble understanding what effect snap caps would have on the sear. The sear/hammer contact area "breaks" and then the hammer falls. The hammer then hits the firing pin which then hits either a snap cap, a primer or the frame (or the retainer). It's not much time, but the sear is free of contact when the hammer hits. How would the sear break as shown unless it had a defect in it. P.s. I've seen plenty of casting and forging defects too. These things happen and I agree with the break in type comments.

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